Simulation studies of protein-induced bilayer deformations, and lipid-induced protein tilting, on a mesoscopic model for lipid bilayers with embedded proteins

DEFF Research Database (Denmark)

Venturoli, M.; Smit, B.; Sperotto, Maria Maddalena

2005-01-01

membranes. Here we present a mesoscopic model for lipid bilayers with embedded proteins, which we have studied with the help of the dissipative particle dynamics simulation technique. Because hydrophobic matching is believed to be one of the main physical mechanisms regulating lipid-protein interactions......-induced protein tilt, with the hydrophobic mismatch ( positive and negative) between the protein hydrophobic length and the pure lipid bilayer hydrophobic thickness. The protein-induced bilayer perturbation was quantified in terms of a coherence length, xi(P), of the lipid bilayer hydrophobic thickness pro. le...... for positive values of mismatch; a dependence on the protein size appears as well. In the case of large model proteins experiencing extreme mismatch conditions, in the region next to the so-called lipid annulus, there appears an undershooting ( or overshooting) region where the bilayer hydrophobic thickness...

Exploiting lipopolysaccharide-induced deformation of lipid bilayers to modify membrane composition and generate two-dimensional geometric membrane array patterns

Energy Technology Data Exchange (ETDEWEB)

Adams, Peter G. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Swingle, Kirstie L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of New Mexico, Albuquerque, NM (United States); Paxton, Walter F. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Nogan, John J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Stromberg, Loreen R. [Univ. of New Mexico, Albuquerque, NM (United States); Firestone, Millicent A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mukundan, Harshini [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States); Montaño, Gabriel A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2015-05-27

Supported lipid bilayers have proven effective as model membranes for investigating biophysical processes and in development of sensor and array technologies. The ability to modify lipid bilayers after their formation and in situ could greatly advance membrane technologies, but is difficult via current state-of-the-art technologies. Here we demonstrate a novel method that allows the controlled post-formation processing and modification of complex supported lipid bilayer arrangements, under aqueous conditions. We exploit the destabilization effect of lipopolysaccharide, an amphiphilic biomolecule, interacting with lipid bilayers to generate voids that can be backfilled to introduce desired membrane components. We further demonstrate that when used in combination with a single, traditional soft lithography process, it is possible to generate hierarchically-organized membrane domains and microscale 2-D array patterns of domains. Significantly, this technique can be used to repeatedly modify membranes allowing iterative control over membrane composition. This approach expands our toolkit for functional membrane design, with potential applications for enhanced materials templating, biosensing and investigating lipid-membrane processes.

Interaction of saponin 1688 with phase separated lipid bilayers.

Science.gov (United States)

Chen, Maohui; Balhara, Vinod; Jaimes Castillo, Ana Maria; Balsevich, John; Johnston, Linda J

2017-07-01

Saponins are a diverse family of naturally occurring plant triterpene or steroid glycosides that have a wide range of biological activities. They have been shown to permeabilize membranes and in some cases membrane disruption has been hypothesized to involve saponin/cholesterol complexes. We have examined the interaction of steroidal saponin 1688-1 with lipid membranes that contain cholesterol and have a mixture of liquid-ordered (L o ) and liquid-disordered (L d ) phases as a model for lipid rafts in cellular membranes. A combination of atomic force microscopy (AFM) and fluorescence was used to probe the effect of saponin on the bilayer. The results demonstrate that saponin forms defects in the membrane and also leads to formation of small aggregates on the membrane surface. Although most of the membrane damage occurs in the liquid-disordered phase, fluorescence results demonstrate that saponin localizes in both ordered and disordered membrane phases, with a modest preference for the disordered regions. Similar effects are observed for both direct incorporation of saponin in the lipid mixture used to make vesicles/bilayers and for incubation of saponin with preformed bilayers. The results suggest that the initial sites of interaction are at the interface between the domains and surrounding disordered phase. The preference for saponin localization in the disordered phase may reflect the ease of penetration of saponin into a less ordered membrane, rather than the actual cholesterol concentration in the membrane. Dye leakage assays indicate that a high concentration of saponin is required for membrane permeabilization consistent with the supported lipid bilayer experiments. Crown Copyright © 2017. Published by Elsevier B.V. All rights reserved.

Viscoelastic deformation of lipid bilayer vesicles.

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Wu, Shao-Hua; Sankhagowit, Shalene; Biswas, Roshni; Wu, Shuyang; Povinelli, Michelle L; Malmstadt, Noah

2015-10-07

Lipid bilayers form the boundaries of the cell and its organelles. Many physiological processes, such as cell movement and division, involve bending and folding of the bilayer at high curvatures. Currently, bending of the bilayer is treated as an elastic deformation, such that its stress-strain response is independent of the rate at which bending strain is applied. We present here the first direct measurement of viscoelastic response in a lipid bilayer vesicle. We used a dual-beam optical trap (DBOT) to stretch 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) giant unilamellar vesicles (GUVs). Upon application of a step optical force, the vesicle membrane deforms in two regimes: a fast, instantaneous area increase, followed by a much slower stretching to an eventual plateau deformation. From measurements of dozens of GUVs, the average time constant of the slower stretching response was 0.225 ± 0.033 s (standard deviation, SD). Increasing the fluid viscosity did not affect the observed time constant. We performed a set of experiments to rule out heating by laser absorption as a cause of the transient behavior. Thus, we demonstrate here that the bending deformation of lipid bilayer membranes should be treated as viscoelastic.

Influence of ester-modified lipids on bilayer structure.

Science.gov (United States)

Villanueva, Diana Y; Lim, Joseph B; Klauda, Jeffery B

2013-11-19

Lipid membranes function as barriers for cells to prevent unwanted chemicals from entering the cell and wanted chemicals from leaving. Because of their hydrophobic interior, membranes do not allow water to penetrate beyond the headgroup region. We performed molecular simulations to examine the effects of ester-modified lipids, which contain ester groups along their hydrocarbon chains, on bilayer structure. We chose two lipids from those presented in Menger et al. [J. Am. Chem. Soc. 2006, 128, 14034] with ester groups in (1) the upper half of the lipid chain (MEPC) and (2) the middle and end of the lipid chain (MGPC). MGPC (30%)/POPC bilayers formed stable water pores of diameter 5-7 Å, but MGPC (22%)/POPC and MEPC (30%)/POPC bilayers did not form these defects. These pores were similar to those formed during electroporation; i.e., the head groups lined the pore and allowed water and ions to transport across the bilayer. However, we found that lateral organization of the MGPC lipids into clusters, instead of an electric field or charge disparity as in electroporation, was essential for pore formation. On the basis of this, we propose an overall mechanism for pore formation. The similarities between the ester-modified lipids and byproducts of lipid peroxidation with multiple hydrophilic groups in the middle of the chain suggest that free radical reactions with unsaturated lipids and sterols result in fundamental changes that may be similar to what is seen in bilayers with ester-modified lipids.

Fusion of raft-like lipid bilayers operated by a membranotropic domain of the HSV-type I glycoprotein gH occurs through a cholesterol-dependent mechanism.

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Vitiello, Giuseppe; Falanga, Annarita; Petruk, Ariel Alcides; Merlino, Antonello; Fragneto, Giovanna; Paduano, Luigi; Galdiero, Stefania; D'Errico, Gerardino

2015-04-21

A wealth of evidence indicates that lipid rafts are involved in the fusion of the viral lipid envelope with the target cell membrane. However, the interplay between these sterol- and sphingolipid-enriched ordered domains and viral fusion glycoproteins has not yet been clarified. In this work we investigate the molecular mechanism by which a membranotropic fragment of the glycoprotein gH of the Herpes Simplex Virus (HSV) type I (gH625) drives fusion of lipid bilayers formed by palmitoyl oleoyl phosphatidylcholine (POPC)-sphingomyelin (SM)-cholesterol (CHOL) (1 : 1 : 1 wt/wt/wt), focusing on the role played by each component. The comparative analysis of the liposome fusion assays, Dynamic Light Scattering (DLS), spectrofluorimetry, Neutron Reflectivity (NR) and Electron Spin Resonance (ESR) experiments, and Molecular Dynamics (MD) simulations shows that CHOL is fundamental for liposome fusion to occur. In detail, CHOL stabilizes the gH625-bilayer association by specific interactions with the peptide Trp residue. The interaction with gH625 causes an increased order of the lipid acyl chains, whose local rotational motion is significantly hampered. SM plays only a minor role in the process, favoring the propagation of lipid perturbation to the bilayer inner core. The stiffening of the peptide-interacting bilayer leaflet results in an asymmetric perturbation of the membrane, which is locally destabilized thus favoring fusion events. Our results show that viral fusion glycoproteins are optimally suited to exert a high fusogenic activity on lipid rafts and support the relevance of cholesterol as a key player of membrane-related processes.

Theory of Kinetics of Registration and Anti-Registration in Lipid Bilayers

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Olmsted, Peter; Williamson, John

Lipid bilayer leaflets are often treated as if they are coupled; i.e., that the two leaflets undergo simultaneous transitions between phases, and that domains involve both leaflets together in a registered fashion. We present theory and simulation showing how interleaflet couplings and hydrophobic mismatch can lead to a complex phase diagram with multiple metastable two-phase and three-phase states. Many of these states can be discerned in the experimental literature, and are expected in the early stages of coarsening when domains are sub-micron (and thus perhaps of significance to lipid rafts). We present different kinetic scenarios for transitions between these state, and show how lipid flip flop can surprisingly lead to non-symmetric anti-registered patterns.

Finding a needle in a haystack: the role of electrostatics in target lipid recognition by PH domains.

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Craig N Lumb

Full Text Available Interactions between protein domains and lipid molecules play key roles in controlling cell membrane signalling and trafficking. The pleckstrin homology (PH domain is one of the most widespread, binding specifically to phosphatidylinositol phosphates (PIPs in cell membranes. PH domains must locate specific PIPs in the presence of a background of approximately 20% anionic lipids within the cytoplasmic leaflet of the plasma membrane. We investigate the mechanism of such recognition via a multiscale procedure combining Brownian dynamics (BD and molecular dynamics (MD simulations of the GRP1 PH domain interacting with phosphatidylinositol (3,4,5-trisphosphate (PI(3,4,5P₃. The interaction of GRP1-PH with PI(3,4,5P₃ in a zwitterionic bilayer is compared with the interaction in bilayers containing different levels of anionic 'decoy' lipids. BD simulations reveal both translational and orientational electrostatic steering of the PH domain towards the PI(3,4,5P₃-containing anionic bilayer surface. There is a payoff between non-PIP anionic lipids attracting the PH domain to the bilayer surface in a favourable orientation and their role as 'decoys', disrupting the interaction of GRP1-PH with the PI(3,4,5P₃ molecule. Significantly, approximately 20% anionic lipid in the cytoplasmic leaflet of the bilayer is nearly optimal to both enhance orientational steering and to localise GRP1-PH proximal to the surface of the membrane without sacrificing its ability to locate PI(3,4,5P₃ within the bilayer plane. Subsequent MD simulations reveal binding to PI(3,4,5P₃, forming protein-phosphate contacts comparable to those in X-ray structures. These studies demonstrate a computational framework which addresses lipid recognition within a cell membrane environment, offering a link between structural and cell biological characterisation.

Alcohol's Effects on Lipid Bilayer Properties

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Ingólfsson, Helgi I.; Andersen, Olaf S.

2011-01-01

Alcohols are known modulators of lipid bilayer properties. Their biological effects have long been attributed to their bilayer-modifying effects, but alcohols can also alter protein function through direct protein interactions. This raises the question: Do alcohol's biological actions result predominantly from direct protein-alcohol interactions or from general changes in the membrane properties? The efficacy of alcohols of various chain lengths tends to exhibit a so-called cutoff effect (i.e., increasing potency with increased chain length, which that eventually levels off). The cutoff varies depending on the assay, and numerous mechanisms have been proposed such as: limited size of the alcohol-protein interaction site, limited alcohol solubility, and a chain-length-dependent lipid bilayer-alcohol interaction. To address these issues, we determined the bilayer-modifying potency of 27 aliphatic alcohols using a gramicidin-based fluorescence assay. All of the alcohols tested (with chain lengths of 1–16 carbons) alter the bilayer properties, as sensed by a bilayer-spanning channel. The bilayer-modifying potency of the short-chain alcohols scales linearly with their bilayer partitioning; the potency tapers off at higher chain lengths, and eventually changes sign for the longest-chain alcohols, demonstrating an alcohol cutoff effect in a system that has no alcohol-binding pocket. PMID:21843475

Viscoelastic deformation of lipid bilayer vesicles†

Science.gov (United States)

Wu, Shao-Hua; Sankhagowit, Shalene; Biswas, Roshni; Wu, Shuyang; Povinelli, Michelle L.

2015-01-01

Lipid bilayers form the boundaries of the cell and its organelles. Many physiological processes, such as cell movement and division, involve bending and folding of the bilayer at high curvatures. Currently, bending of the bilayer is treated as an elastic deformation, such that its stress-strain response is independent of the rate at which bending strain is applied. We present here the first direct measurement of viscoelastic response in a lipid bilayer vesicle. We used a dual-beam optical trap (DBOT) to stretch 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) giant unilamellar vesicles (GUVs). Upon application of a step optical force, the vesicle membrane deforms in two regimes: a fast, instantaneous area increase, followed by a much slower stretching to an eventual plateau deformation. From measurements of dozens of GUVs, the average time constant of the slower stretching response was 0.225 ± 0.033 s (standard deviation, SD). Increasing the fluid viscosity did not affect the observed time constant. We performed a set of experiments to rule out heating by laser absorption as a cause of the transient behavior. Thus, we demonstrate here that the bending deformation of lipid bilayer membranes should be treated as viscoelastic. PMID:26268612

Probing Lipid Bilayers under Ionic Imbalance.

Science.gov (United States)

Lin, Jiaqi; Alexander-Katz, Alfredo

2016-12-06

Biological membranes are normally under a resting transmembrane potential (TMP), which originates from the ionic imbalance between extracellular fluids and cytosols, and serves as electric power storage for cells. In cell electroporation, the ionic imbalance builds up a high TMP, resulting in the poration of cell membranes. However, the relationship between ionic imbalance and TMP is not clearly understood, and little is known about the effect of ionic imbalance on the structure and dynamics of biological membranes. In this study, we used coarse-grained molecular dynamics to characterize a dipalmitoylphosphatidylcholine bilayer system under ionic imbalances ranging from 0 to ∼0.06 e charges per lipid (e/Lip). We found that the TMP displayed three distinct regimes: 1) a linear regime between 0 and 0.045 e/Lip, where the TMP increased linearly with ionic imbalance; 2) a yielding regime between ∼0.045 and 0.060 e/Lip, where the TMP displayed a plateau; and 3) a poration regime above ∼0.060 e/Lip, where we observed pore formation within the sampling time (80 ns). We found no structural changes in the linear regime, apart from a nonlinear increase in the area per lipid, whereas in the yielding regime the bilayer exhibited substantial thinning, leading to an excess of water and Na + within the bilayer, as well as significant misalignment of the lipid tails. In the poration regime, lipid molecules diffused slightly faster. We also found that the fluid-to-gel phase transition temperature of the bilayer dropped below the normal value with increased ionic imbalances. Our results show that a high ionic imbalance can substantially alter the essential properties of the bilayer, making the bilayer more fluid like, or conversely, depolarization of a cell could in principle lead to membrane stiffening. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Characterization of the transverse relaxation rates in lipid bilayers

International Nuclear Information System (INIS)

Watnick, P.I.; Dea, P.; Chan, S.I.

1990-01-01

The 2H NMR transverse relaxation rates of a deuterated phospholipid bilayer reflect slow motions in the bilayer membrane. A study of dimyristoyl lecithin specifically deuterated at several positions of the hydrocarbon chains indicates that these motions are cooperative and are confined to the hydrocarbon chains of the lipid bilayer. However, lipid head group interactions do play an important role in modulating the properties of the cooperative fluctuations of the hydrocarbon chains (director fluctuations), as evidenced by the effects of various lipid additives on the 2H NMR transverse relaxation rates of the dimyristoyl lecithin bilayer

Poly(amidoamine) dendrimers on lipid bilayers II: Effects of bilayer phase and dendrimer termination.

Science.gov (United States)

Kelly, Christopher V; Leroueil, Pascale R; Orr, Bradford G; Banaszak Holl, Mark M; Andricioaei, Ioan

2008-08-07

The molecular structures and enthalpy release of poly(amidoamine) (PAMAM) dendrimers binding to 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers were explored through atomistic molecular dynamics. Three PAMAM dendrimer terminations were examined: protonated primary amine, neutral acetamide, and deprotonated carboxylic acid. Fluid and gel lipid phases were examined to extract the effects of lipid tail mobility on the binding of generation-3 dendrimers, which are directly relevant to the nanoparticle interactions involving lipid rafts, endocytosis, lipid removal, and/or membrane pores. Upon binding to gel phase lipids, dendrimers remained spherical, had a constant radius of gyration, and approximately one-quarter of the terminal groups were in close proximity to the lipids. In contrast, upon binding to fluid phase bilayers, dendrimers flattened out with a large increase in their asphericity and radii of gyration. Although over twice as many dendrimer-lipid contacts were formed on fluid versus gel phase lipids, the dendrimer-lipid interaction energy was only 20% stronger. The greatest enthalpy release upon binding was between the charged dendrimers and the lipid bilayer. However, the stronger binding to fluid versus gel phase lipids was driven by the hydrophobic interactions between the inner dendrimer and lipid tails.

A model of lipid rearrangements during pore formation in the DPPC lipid bilayer.

Science.gov (United States)

Wrona, Artur; Kubica, Krystian

2017-07-10

The molecular bases of pore formation in the lipid bilayer remain unclear, as do the exact characteristics of their sizes and distributions. To understand this process, numerous studies have been performed on model lipid membranes including cell-sized giant unilamellar vesicles (GUV). The effect of an electric field on DPPC GUV depends on the lipid membrane state: in the liquid crystalline phase the created pores have a cylinder-like shape, whereas in the gel phase a crack has been observed. The aim of the study was to investigate the geometry of pores created in a lipid bilayer in gel and liquid crystalline phases in reference to literature experimental data. A mathematical model of the pore in a DPPC lipid bilayer developed based on the law of conservation of mass and the assumption of constant volume of lipid molecules, independent of their conformation, allows for analysis of pore shape and accompanying molecular rearrangements. The membrane area occupied by the pore of a cylinder-like shape is greater than the membrane area occupied by lipid molecules creating the pore structure (before pore appearance). Creation of such pores requires more space, which can be achieved by conformational changes of lipid chains toward a more compact state. This process is impossible for a membrane in the most compact, gel phase. We show that the geometry of the pores formed in the lipid bilayer in the gel phase must be different from the cylinder shape formed in the lipid bilayer in a liquid crystalline state, confirming experimental studies. Furthermore, we characterize the occurrence of the 'buffer' zone surrounding pores in the liquid crystalline phase as a mechanism of separation of neighbouring pores.

Biomimetic Cationic Nanoparticles Based on Silica: Optimizing Bilayer Deposition from Lipid Films

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Rodrigo T. Ribeiro

2017-10-01

Full Text Available The optimization of bilayer coverage on particles is important for a variety of biomedical applications, such as drug, vaccine, and genetic material delivery. This work aims at optimizing the deposition of cationic bilayers on silica over a range of experimental conditions for the intervening medium and two different assemblies for the cationic lipid, namely, lipid films or pre-formed lipid bilayer fragments. The lipid adsorption on silica in situ over a range of added lipid concentrations was determined from elemental analysis of carbon, hydrogen, and nitrogen and related to the colloidal stability, sizing, zeta potential, and polydispersity of the silica/lipid nanoparticles. Superior bilayer deposition took place from lipid films, whereas adsorption from pre-formed bilayer fragments yielded limiting adsorption below the levels expected for bilayer adsorption.

Observation of undulation motion of lipid bilayers by neutron spin echo

International Nuclear Information System (INIS)

Yamada, Norifumi L.; Seto, Hideki; Hishida, Mafumi

2010-01-01

Aqueous solutions of synthesized phospholipids have been well investigated as model biomembranes. These lipids usually self-assemble into regular stacks of bilayers with a characteristic repeat distance on the order of nm, whereas real biomembrane exist as single bilayers. The key phenomenon in understanding the formation of single isolated bilayers in 'unbinding' of lipid bilayers, in which the inter-bilayer distance of lipid bilayers diverges by the steric interaction due to the membrane undulation. In this paper, we show some results of neutron spin-echo (NSE) experiments to investigate the effect of the steric interaction on unbinding and related phenomena. (author)

Multinuclear NMR studies of single lipid bilayers supported in cylindrical aluminum oxide nanopores.

Science.gov (United States)

Gaede, Holly C; Luckett, Keith M; Polozov, Ivan V; Gawrisch, Klaus

2004-08-31

Lipid bilayers were deposited inside the 0.2 microm pores of anodic aluminum oxide (AAO) filters by extrusion of multilamellar liposomes and their properties studied by 2H, 31P, and 1H solid-state NMR. Only the first bilayer adhered strongly to the inner surface of the pores. Additional layers were washed out easily by a flow of water as demonstrated by 1H magic angle spinning NMR experiments with addition of Pr3+ ions to shift accessible lipid headgroup resonances. A 13 mm diameter Anopore filter of 60 microm thickness oriented approximately 2.5 x 10(-7) mol of lipid as a single bilayer, corresponding to a total membrane area of about 500 cm2. The 2H NMR spectra of chain deuterated POPC are consistent with adsorption of wavy, tubular bilayers to the inner pore surface. By NMR diffusion experiments, we determined the average length of those lipid tubules to be approximately 0.4 microm. There is evidence for a thick water layer between lipid tubules and the pore surface. The ends of tubules are well sealed against the pore such that Pr3+ ions cannot penetrate into the water underneath the bilayers. We successfully trapped poly(ethylene glycol) (PEG) with a molecular weight of 8000 in this water layer. From the quantity of trapped PEG, we calculated an average water layer thickness of 3 nm. Lipid order parameters and motional properties are unperturbed by the solid support, in agreement with existence of a water layer. Such unperturbed, solid supported membranes are ideal for incorporation of membrane-spanning proteins with large intra- and extracellular domains. The experiments suggest the promise of such porous filters as membrane support in biosensors.

Proton permeation of lipid bilayers.

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Deamer, D W

1987-10-01

Proton permeation of the lipid bilayer barrier has two unique features. First, permeability coefficients measured at neutral pH ranges are six to seven orders of magnitude greater than expected from knowledge of other monovalent cations. Second, proton conductance across planar lipid bilayers varies at most by a factor of 10 when pH is varied from near 1 to near 11. Two mechanisms have been proposed to account for this anomalous behavior: proton conductance related to contaminants of lipid bilayers, and proton translocation along transient hydrogen-bonded chains (tHBC) of associated water molecules in the membrane. The weight of evidence suggests that trace contaminants may contribute to proton conductance across planar lipid membranes at certain pH ranges, but cannot account for the anomalous proton flux in liposome systems. Two new results will be reported here which were designed to test the tHBC model. These include measurements of relative proton/potassium permeability in the gramicidin channel, and plots of proton flux against the magnitude of pH gradients. (1) The relative permeabilities of protons and potassium through the gramicidin channel, which contains a single strand of hydrogen-bonded water molecules, were found to differ by at least four orders of magnitude when measured at neutral pH ranges. This result demonstrates that a hydrogen-bonded chain of water molecules can provide substantial discrimination between protons and other cations. It was also possible to calculate that if approximately 7% of bilayer water was present in a transient configuration similar to that of the gramicidin channel, it could account for the measured proton flux. (2) The plot of proton conductance against pH gradient across liposome membranes was superlinear, a result that is consistent with one of three alternative tHBC models for proton conductance described by Nagle elsewhere in this volume.

Imaging lipid domains in cell membranes: the advent of super-resolution fluorescence microscopy

Directory of Open Access Journals (Sweden)

Dylan Myers Owen

2013-12-01

Full Text Available The lipid bilayer of model membranes, liposomes reconstituted from cell lipids, and plasma membrane vesicles and spheres can separate into two distinct liquid phases to yield lipid domains with liquid-ordered and liquid-disordered properties. These observations are the basis of the lipid raft hypothesis that postulates the existence of cholesterol-enriched ordered-phase lipid domains in cell membranes that could regulate protein mobility, localization and interaction. Here we review the evidence that nano-scaled lipid complexes and meso-scaled lipid domains exist in cell membranes and how new fluorescence microscopy techniques that overcome the diffraction limit provide new insights into lipid organization in cell membranes.

GABA_A receptor function is regulated by lipid bilayer elasticity

DEFF Research Database (Denmark)

Søgaard, Rikke; Werge, Thomas; Berthelsen, Camilla

2006-01-01

( s) underlying these effects are poorly understood. DHA and Triton X-100, at concentrations that affect GABAA receptor function, increase the elasticity of lipid bilayers measured as decreased bilayer stiffness using gramicidin channels as molecular force transducers. We have previously shown...... reduced the peak amplitude of the GABA-induced currents and increased the rate of receptor desensitization. The effects of the amphiphiles did not correlate with the expected changes in monolayer spontaneous curvature. We conclude that GABAA receptor function is regulated by lipid bilayer elasticity....... PUFAs may generally regulate membrane protein function by affecting the elasticity of the host lipid bilayer....

Dynamics, Surface Electrostatics and Phase Properties of Nanoscale Curved Lipid Bilayers

Science.gov (United States)

Koolivand, Amir

Surface electrostatic potential of a lipid bilayer governs many vital functions of living cells. Several classes of proteins are known of exhibiting strong binding preferences to curved lipid bilayer surfaces. In this project we employed electron paramagnetic resonance (EPR) of a recently introduced phospholipid (IMTSL-PTE) bearing a pH-sensitive nitroxide covalently attached to the lipid head group to measure the surface electrostatics of the lipid membrane and nanopore-confined lipid bilayers as a function of the bilayer curvature. The pKa of the ionizable group of this lipid-based spin probe is reporting on the bilayer surface electrostatics potential by changes in the EPR spectra. Specifically, both rotational dynamics and magnetic parameters of the nitroxide are affected by the probe protonation. Effect of curvature on the surface electrostatic potential and dynamics of lipid bilayer was studied for POPG and DMPG unilamellar vesicles (ULVs). It was found that the magnitude of the negative surface electrostatic potential increased upon decrease in the vesicle diameter for the bilayers in the fluid phase; however, no significant changes were observed for DMPG ULVs in a gel phase. We speculate that biologically relevant fluid bilayer phase allows for a larger variability in the lipid packing density in the lipid polar head group region than a more ordered gel phase and it is likely that the lipid flip-flop is responsible for pH equilibration of IMTSL-PTE. The kinetic EPR study of nitroxide reduction showed that the rate of flip-flop is in the order of 10-5 s-1. The flip-flop rate constant increases when vesicle size deceases. Oxygen permeability measured by X-ban EPR decreases in higher curved vesicles---an observation that is consistent with a tighter packing in smaller vesicles. Partitioning of a small nitroxide molecule TEMPO into ULVs was measured by X-band (9 GHz) and W-band (95 GHz) EPR spectroscopy. The partitioning coefficient of this probe in the lipid

Phase separation in lipid bilayers triggered by low pH

International Nuclear Information System (INIS)

Suresh, Swetha; Edwardson, J. Michael

2010-01-01

Research highlights: → Lipid bilayers have been imaged by atomic force microscopy (AFM). → At pH 5 phase separation occurs in lipid bilayers containing mixed acyl chains. → Phase separation does not occur when lipids have only unsaturated chains. → Phase separation might drive protein clustering during endocytosis. -- Abstract: Endocytosis involves the capture of membrane from the cell surface in the form of vesicles, which become rapidly acidified to about pH 5. Here we show using atomic force microscopy (AFM) imaging that this degree of acidification triggers phase separation in lipid bilayers containing mixed acyl chains (e.g. palmitoyl/oleoyl) or complex mixtures (e.g. total brain extract) but not in bilayers containing only lipids with unsaturated chains (e.g. dioleoyl). Since mixed-chain lipids are major constituents of the outer leaflet of the plasma membrane, the type of phase separation reported here might support protein clustering and signaling during endocytosis.

Molecular Simulations of Sequence-Specific Association of Transmembrane Proteins in Lipid Bilayers

Science.gov (United States)

Doxastakis, Manolis; Prakash, Anupam; Janosi, Lorant

2011-03-01

Association of membrane proteins is central in material and information flow across the cellular membranes. Amino-acid sequence and the membrane environment are two critical factors controlling association, however, quantitative knowledge on such contributions is limited. In this work, we study the dimerization of helices in lipid bilayers using extensive parallel Monte Carlo simulations with recently developed algorithms. The dimerization of Glycophorin A is examined employing a coarse-grain model that retains a level of amino-acid specificity, in three different phospholipid bilayers. Association is driven by a balance of protein-protein and lipid-induced interactions with the latter playing a major role at short separations. Following a different approach, the effect of amino-acid sequence is studied using the four transmembrane domains of the epidermal growth factor receptor family in identical lipid environments. Detailed characterization of dimer formation and estimates of the free energy of association reveal that these helices present significant affinity to self-associate with certain dimers forming non-specific interfaces.

Lipid Bilayer Formation on Organic Electronic Materials

KAUST Repository

Zhang, Yi

2018-04-23

The lipid bilayer is the elemental structure of cell membrane, forming a stable barrier between the interior and exterior of the cell while hosting membrane proteins that enable selective transport of biologically important compounds and cellular recognition. Monitoring the quality and function of lipid bilayers is thus essential and can be performed using electrically active substrates that allow for transduction of signals. Such a promising electronic transducer material is the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) which has provided a plethora of novel bio transducing architectures. The challenge is however in assembling a bilayer on the conducting polymer surface, which is defect-free and has high mobility. Herein, we investigate the fusion of zwitterionic vesicles on a variety of PEDOT:PSS films, but also on an electron transporting, negatively charged organic semiconductor, in order to understand the surface properties that trigger vesicle fusion. The PEDOT:PSS films are prepared from dispersions containing different concentrations of ethylene glycol included as a formulation additive, which gives a handle to modulate surface physicochemical properties without a compromise on the chemical composition. The strong correlation between the polarity of the surface, the fusion of vesicles and the mobility of the resulting bilayer aides extracting design principles for the development of future conducting polymers that will enable the formation of lipid bilayers.

Molecular modeling of proteinlike inclusions in lipid bilayers: lipid-mediated interactions.

Science.gov (United States)

Kik, Richard A; Leermakers, Frans A M; Kleijn, J Mieke

2010-02-01

We investigated the insertion of transmembrane structures in a lipid bilayer and their interactions using self-consistent field theory. The lipids are coarse-grained on a united-atom level and consist of a phosphatidylcholinelike headgroup and two hydrophobic tails. The inclusions, acting as simple models for proteins that span biological membranes, are rigid rods (radius R ) with a hydrophobic surface and hydrophilic end caps. The insertion free energy Omega of an individual rod is strongly regulated by the affinity between its hydrophobic surface and the lipid tails. This affinity also controls the best match of the hydrophobic length of the rod with that of the bilayer. The line tension tau(=Omega/2piR) is practically independent of R . The perturbations in the bilayer as a function of distance from the inclusion, have the shape of a damped oscillation. The wavelength and decay length are related to the elastic properties of the bilayer and do not depend on R . These results are used to analyze how the lipid matrix affects the interaction between transmembrane objects, for computational reasons considering the limit of R-->infinity . Contributions on different length scales can be distinguished: (i) a long-range elastic interaction, which is an exponentially decaying oscillation; (ii) an exponentially decaying repulsion on an intermediate length scale, resulting from the loss of conformational entropy of the lipid tails; and (iii) a short-range interaction due to the finite compressibility of the lipid tails, which manifests either as a depletion attraction if there is no affinity between the tails and the inclusions' surface or, otherwise, as an oscillatory structural force.

Pairing of cholesterol with oxidized phospholipid species in lipid bilayers

DEFF Research Database (Denmark)

Khandelia, Himanshu; Loubet, Bastien; Olzynska, Agnieszka

2014-01-01

We claim that (1) cholesterol protects bilayers from disruption caused by lipid oxidation by sequestering conical shaped oxidized lipid species such as 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PZPC) away from phospholipid, because cholesterol and the oxidized lipid have complementary...... shapes and (2) mixtures of cholesterol and oxidized lipids can self-assemble into bilayers much like lysolipid–cholesterol mixtures. The evidence for bilayer protection comes from molecular dynamics (MD) simulations and dynamic light scattering (DLS) measurements. Unimodal size distributions of extruded...... vesicles (LUVETs) made up of a mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and PZPC containing high amounts of PZPC are only obtained when cholesterol is present in high concentrations. In simulations, bilayers containing high amounts of PZPC become porous, unless cholesterol is also present...

Fragmented state of lipid bilayers in water

DEFF Research Database (Denmark)

Helfrich, W.; Thimmel, J.; Klösgen, Beate Maria

1999-01-01

The bilayers of some typical biological membrane lipids such as PC and DGDG disintegrate in a large excess of water to form an optically invisible dispersive bilayer phase. `Dark bodies' can be reversibly precipitated from it by raising the temperature. The dispersive phase probably consists...

Effect of low levels of lipid oxidation on the curvature, dynamics, and permeability of lipid bilayers and their interactions with cationic nanoparticles

Science.gov (United States)

Lee, Hwankyu; Malmstadt, Noah

2018-04-01

Lipid bilayers composed of saturated and unsaturated lipids, oxidized lipids, and cholesterol at concentrations of 0–18 mol% oxidized lipid were simulated, showing that the presence of oxidized lipid increases bilayer disorder, curvature, and lateral dynamics at low oxidized-lipid concentrations of 18 mol% or less. The aldehyde terminal of a shortened oxidized-lipid tail tends to interact with water and thus bends toward the bilayer-water interface, in agreement with previous experiments and simulations. In particular, water molecules pass through the oxidized bilayer without pore formation, implying passive permeability. A single nanoparticle, which consists of 300 polystyrene (PS) chains with cationic terminals, added to this bilayer simulation induces negative bilayer curvature and inserts to the bilayer, regardless of the oxidized-lipid concentration. Hydrophobic monomers and cationic terminals of the PS particle interact respectively with lipid tails and headgroups, leading to the wrapping of either lipid monolayer or bilayer along the particle surface. These results indicate that lipid oxidation increases membrane curvature and permeability even at such a low concentration of oxidized lipid, which supports the experimental observations regarding the passive permeability of oxidized bilayer, and also that oxidized lipids of low concentration do not significantly influence the insertion of a cationic PS particle to the bilayer.

Cationic Dimyristoylphosphatidylcholine and Dioleoyloxytrimethylammonium Propane Lipid Bilayers: Atomistic Insight for Structure and Dynamics

DEFF Research Database (Denmark)

Zhao, W.; Gurtovenko, A. A.; Vattulainen, I.

2012-01-01

We performed atomistic molecular dynamics simulations of lipid bilayers consisting of a mixture of cationic dioleoyloxytrimethylammonium propane (DOTAP) and zwitterionic dimyristoylphosphatidylcholine (DMPC) lipids at different DOTAP fractions. Our primary focus was the specific effects...... of unsaturated lipid chains on structural and dynamic properties of mixed cationic bilayers. The bilayer area, as well as the ordering of lipid tails, shows a pronounced nonmonotonic behavior when TAP lipid fraction increases. The minimum in area (maximum in ordering) was observed for a bilayer with TAP fraction...... lipids, which were found to form PC-PC and PC-TAP pairs, and the formation of lipid clusters....

SFG studies on interactions between antimicrobial peptides and supported lipid bilayers.

Science.gov (United States)

Chen, Xiaoyun; Chen, Zhan

2006-09-01

The mode of action of antimicrobial peptides (AMPs) in disrupting cell membrane bilayers is of fundamental importance in understanding the efficiency of different AMPs, which is crucial to design antibiotics with improved properties. Recent developments in the field of sum frequency generation (SFG) vibrational spectroscopy have made it a powerful and unique biophysical technique in investigating the interactions between AMPs and a single substrate supported planar lipid bilayer. We will review some of the recent progress in applying SFG to study membrane lipid bilayers and discuss how SFG can provide novel information such as real-time bilayer structure change and AMP orientation during AMP-lipid bilayer interactions in a very biologically relevant manner. Several examples of applying SFG to monitor such interactions between AMPs and a dipalmitoyl phosphatidylglycerol (DPPG) bilayer are presented. Different modes of actions are observed for melittin, tachyplesin I, d-magainin 2, MSI-843, and a synthetic antibacterial oligomer, demonstrating that SFG is very effective in the study of AMPs and AMP-lipid bilayer interactions.

A criterion to identify the equilibration time in lipid bilayer simulations

Directory of Open Access Journals (Sweden)

Rodolfo D. Porasso

2012-11-01

Full Text Available With the aim of establishing a criterion for identifying when a lipid bilayer has reached steady state using the molecular dynamics simulation technique, lipid bilayers of different composition in their liquid crystalline phase were simulated in aqueous solution in presence of CaCl_2 as electrolyte, at different concentration levels. In this regard, we used two different lipid bilayer systems: one composed by 288 DPPC (DiPalmitoylPhosphatidylCholine and another constituted by 288 DPPS (DiPalmitoylPhosphatidylSerine. In this sense, for both type of lipid bilayers, we have studied the temporal evolution of some lipids properties, such as the surface area per lipid, the deuterium order parameter, the lipid hydration and the lipid-calcium coordination. From their analysis, it became evident how each property has a different time to achieve equilibrium. The following order was found, from faster property to slower property: coordination of ions $approx$ deuterium order parameter > area per lipid $approx$ hydration. Consequently, when the hydration of lipids or the mean area per lipid are stable, we can ensure that the lipid membrane has reached the steady state.

DNA nanotechnology: Bringing lipid bilayers into shape

Science.gov (United States)

Howorka, Stefan

2017-07-01

Lipid bilayers form the thin and floppy membranes that define the boundary of compartments such as cells. Now, a method to control the shape and size of bilayers using DNA nanoscaffolds has been developed. Such designer materials advance synthetic biology and could find use in membrane research.

Cholesterol Protects the Oxidized Lipid Bilayer from Water Injury

DEFF Research Database (Denmark)

Owen, Michael C; Kulig, Waldemar; Rog, Tomasz

2018-01-01

In an effort to delineate how cholesterol protects membrane structure under oxidative stress conditions, we monitored the changes to the structure of lipid bilayers comprising 30 mol% cholesterol and an increasing concentration of Class B oxidized 1-palmitoyl-2-oleoylphosphatidylcholine (POPC...... in a characteristic reduction in bilayer thickness and increase in area per lipid, thereby increasing the exposure of the membrane hydrophobic region to water. However, cholesterol was observed to help reduce water injury by moving into the bilayer core and forming more hydrogen bonds with the oxPLs. Cholesterol also...... resists altering its tilt angle, helping to maintain membrane integrity. Water that enters the 1-nm-thick core region remains part of the bulk water on either side of the bilayer, with relatively few water molecules able to traverse through the bilayer. In cholesterol-rich membranes, the bilayer does...

Triglyceride blisters in lipid bilayers: implications for lipid droplet biogenesis and the mobile lipid signal in cancer cell membranes.

Directory of Open Access Journals (Sweden)

Himanshu Khandelia

Full Text Available Triglycerides have a limited solubility, around 3%, in phosphatidylcholine lipid bilayers. Using millisecond-scale course grained molecular dynamics simulations, we show that the model lipid bilayer can accommodate a higher concentration of triolein (TO than earlier anticipated, by sequestering triolein molecules to the bilayer center in the form of a disordered, isotropic, mobile neutral lipid aggregate, at least 17 nm in diameter, which forms spontaneously, and remains stable on at least the microsecond time scale. The results give credence to the hotly debated existence of mobile neutral lipid aggregates of unknown function present in malignant cells, and to the early biogenesis of lipid droplets accommodated between the two leaflets of the endoplasmic reticulum membrane. The TO aggregates give the bilayer a blister-like appearance, and will hinder the formation of multi-lamellar phases in model, and possibly living membranes. The blisters will result in anomalous membrane probe partitioning, which should be accounted for in the interpretation of probe-related measurements.

Coexistence of a two-states organization for a cell-penetrating peptide in lipid bilayer.

Science.gov (United States)

Plénat, Thomas; Boichot, Sylvie; Dosset, Patrice; Milhiet, Pierre-Emmanuel; Le Grimellec, Christian

2005-12-01

Primary amphipathic cell-penetrating peptides transport cargoes across cell membranes with high efficiency and low lytic activity. These primary amphipathic peptides were previously shown to form aggregates or supramolecular structures in mixed lipid-peptide monolayers, but their behavior in lipid bilayers remains to be characterized. Using atomic force microscopy, we have examined the interactions of P(alpha), a primary amphipathic cell-penetrating peptide which remains alpha-helical whatever the environment, with dipalmitoylphosphatidylcholine (DPPC) bilayers. Addition of P(alpha) at concentrations up to 5 mol % markedly modified the supported bilayers topography. Long and thin filaments lying flat at the membrane surface coexisted with deeply embedded peptides which induced a local thinning of the bilayer. On the other hand, addition of P(alpha) only exerted very limited effects on the corresponding liposome's bilayer physical state, as estimated from differential scanning calorimetry and diphenylhexatriene fluorescence anisotropy experiments. The use of a gel-fluid phase separated supported bilayers made of a dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine mixture confirmed both the existence of long filaments, which at low peptide concentration were preferentially localized in the fluid phase domains and the membrane disorganizing effects of 5 mol % P(alpha). The simultaneous two-states organization of P(alpha), at the membrane surface and deeply embedded in the bilayer, may be involved in the transmembrane carrier function of this primary amphipathic peptide.

Tethered and Polymer Supported Bilayer Lipid Membranes: Structure and Function

Directory of Open Access Journals (Sweden)

Jakob Andersson

2016-05-01

Full Text Available Solid supported bilayer lipid membranes are model systems to mimic natural cell membranes in order to understand structural and functional properties of such systems. The use of a model system allows for the use of a wide variety of analytical tools including atomic force microscopy, impedance spectroscopy, neutron reflectometry, and surface plasmon resonance spectroscopy. Among the large number of different types of model membranes polymer-supported and tethered lipid bilayers have been shown to be versatile and useful systems. Both systems consist of a lipid bilayer, which is de-coupled from an underlying support by a spacer cushion. Both systems will be reviewed, with an emphasis on the effect that the spacer moiety has on the bilayer properties.

Supported Lipid Bilayers with Phosphatidylethanolamine as the Major Component.

Science.gov (United States)

Sendecki, Anne M; Poyton, Matthew F; Baxter, Alexis J; Yang, Tinglu; Cremer, Paul S

2017-11-21

Phosphatidylethanolamine (PE) is notoriously difficult to incorporate into model membrane systems, such as fluid supported lipid bilayers (SLBs), at high concentrations because of its intrinsic negative curvature. Using fluorescence-based techniques, we demonstrate that having fewer sites of unsaturation in the lipid tails leads to high-quality SLBs because these lipids help to minimize the curvature. Moreover, shorter saturated chains can help maintain the membranes in the fluid phase. Using these two guidelines, we find that up to 70 mol % PE can be incorporated into SLBs at room temperature and up to 90 mol % PE can be incorporated at 37 °C. Curiously, conditions under which three-dimensional tubules project outward from the planar surface as well as conditions under which domain formation occurs can be found. We have employed these model membrane systems to explore the ability of Ni 2+ to bind to PE. It was found that this transition metal ion binds 1000-fold tighter to PE than to phosphatidylcholine lipids. In the future, this platform could be exploited to monitor the binding of other transition metal ions or the binding of antimicrobial peptides. It could also be employed to explore the physical properties of PE-containing membranes, such as phase domain behavior and intermolecular hydrogen bonding.

Model for the structure of the lipid bilayer

International Nuclear Information System (INIS)

Pastor, R.W.; Venable, R.M.; Karplus, M.

1991-01-01

A detailed model for the structure and dynamics of the interior of the lipid bilayer in the liquid crystal phase is presented. The model includes two classes of motion: (i) the internal dynamics of the chains, determined from Brownian dynamics simulations with a continuous version of the Marcelja mean-field potential, and (ii) noncollective reorientation (axial rotation and wobble) of the entire molecule, introduced by a cone model. The basic unit of the model is a single lipid chain with field parameters adjusted to fit the 2H order parameters and the frequency-dependent 13C NMR T1 relaxation times of dipalmitoyl phosphatidylcholine bilayers. The chain configurations obtained from the trajectory are used to construct a representation of the bilayer. The resulting lipid assembly is consistent with NMR, neutron diffraction, surface area, and density data. It indicates that a high degree of chain disorder and entanglement exists in biological membranes

A Molecular Dynamics Study of the Structural and Dynamical Properties of Putative Arsenic Substituted Lipid Bilayers

Directory of Open Access Journals (Sweden)

Ratna Juwita

2013-04-01

Full Text Available Cell membranes are composed mainly of phospholipids which are in turn, composed of five major chemical elements: carbon, hydrogen, nitrogen, oxygen, and phosphorus. Recent studies have suggested the possibility of sustaining life if the phosphorus is substituted by arsenic. Although this issue is still controversial, it is of interest to investigate the properties of arsenated-lipid bilayers to evaluate this possibility. In this study, we simulated arsenated-lipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-arsenocholine (POAC, lipid bilayers using all-atom molecular dynamics to understand basic structural and dynamical properties, in particular, the differences from analogous 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, (POPC lipid bilayers. Our simulations showed that POAC lipid bilayers have distinct structural and dynamical properties from those of native POPC lipid bilayers. Relative to POPC lipid bilayers, POAC lipid bilayers have a more compact structure with smaller lateral areas and greater order. The compact structure of POAC lipid bilayers is due to the fact that more inter-lipid salt bridges are formed with arsenate-choline compared to the phosphate-choline of POPC lipid bilayers. These inter-lipid salt bridges bind POAC lipids together and also slow down the head group rotation and lateral diffusion of POAC lipids. Thus, it would be anticipated that POAC and POPC lipid bilayers would have different biological implications.

Protein-induced bilayer Perturbations: Lipid ordering and hydrophobic coupling

DEFF Research Database (Denmark)

Petersen, Frederic Nicolas Rønne; Laursen, Ib; Bohr, Henrik

2009-01-01

The host lipid bilayer is increasingly being recognized as an important non-specific regulator of membrane protein function. Despite considerable progress the interplay between hydrophobic coupling and lipid ordering is still elusive. We use electron spin resonance (ESR) to study the interaction...... between the model protein gramicidin and lipid bilayers of varying thickness. The free energy of the interaction is up to −6 kJ/mol; thus not strongly favored over lipid–lipid interactions. Incorporation of gramicidin results in increased order parameters with increased protein concentration...... and hydrophobic mismatch. Our findings also show that at high protein:lipid ratios the lipids are motionally restricted but not completely immobilized. Both exchange on and off rate values for the lipid ↔ gramicidin interaction are lowest at optimal hydrophobic matching. Hydrophobic mismatch of few Å results...

New optical method for measuring the bending elasticity of lipid bilayers

International Nuclear Information System (INIS)

Minetti, C; Dubois, F; Vitkova, V; Bivas, I

2016-01-01

The knowledge of the elasticity of lipid bilayer structures is fundamental for new developments in biophysics, pharmacology and biomedical research. Lipid vesicles are readily prepared in laboratory conditions and employed for studying the physical properties of lipid membranes. The thermal fluctuation analysis of the shape of lipid vesicles (or flicker spectroscopy) is one of the experimental methods widely used for the measurement of the bending modulus of lipid bilayers. We present direct phase measurements performed on dilute vesicular suspensions by means of a new optical method exploiting holographic microscopy. For the bending constant of phosphatidylcholine bilayers we report the value of 23k B T in agreement with values previously measured by micropipette aspiration, electrodeformation and flicker spectroscopy of giant lipid vesicles. The application of this novel approach for the evaluation of the bending elasticity of lipid membranes opens the way to future developments in the phase measurements on lipid vesicles for the evaluation of their mechanical constants. (paper)

Supramolecular protein immobilization on lipid bilayers

NARCIS (Netherlands)

Bosmans, R.P.G.; Hendriksen, W.E.; Verheijden, Mark Lloyd; Eelkema, R.; Jonkheijm, Pascal; van Esch, J.H.; Brunsveld, Luc

2015-01-01

Protein immobilization on surfaces, and on lipid bilayers specifically, has great potential in biomolecular and biotechnological research. Of current special interest is the immobilization of proteins using supramolecular noncovalent interactions. This allows for a reversible immobilization and

High-resolution orientation and depth of insertion of the voltage-sensing S4 helix of a potassium channel in lipid bilayers.

Science.gov (United States)

Doherty, Tim; Su, Yongchao; Hong, Mei

2010-08-27

The opening and closing of voltage-gated potassium (Kv) channels are controlled by several conserved Arg residues in the S4 helix of the voltage-sensing domain. The interaction of these positively charged Arg residues with the lipid membrane has been of intense interest for understanding how membrane proteins fold to allow charged residues to insert into lipid bilayers against free-energy barriers. Using solid-state NMR, we have now determined the orientation and insertion depth of the S4 peptide of the KvAP channel in lipid bilayers. Two-dimensional (15)N correlation experiments of macroscopically oriented S4 peptide in phospholipid bilayers revealed a tilt angle of 40 degrees and two possible rotation angles differing by 180 degrees around the helix axis. Remarkably, the tilt angle and one of the two rotation angles are identical to those of the S4 helix in the intact voltage-sensing domain, suggesting that interactions between the S4 segment and other helices of the voltage-sensing domain are not essential for the membrane topology of the S4 helix. (13)C-(31)P distances between the S4 backbone and the lipid (31)P indicate a approximately 9 A local thinning and 2 A average thinning of the DMPC (1,2-dimyristoyl-sn-glycero-3-phosphochloline)/DMPG (1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol) bilayer, consistent with neutron diffraction data. Moreover, a short distance of 4.6 A from the guanidinium C(zeta) of the second Arg to (31)P indicates the existence of guanidinium phosphate hydrogen bonding and salt bridges. These data suggest that the structure of the Kv gating helix is mainly determined by protein-lipid interactions instead of interhelical protein-protein interactions, and the S4 amino acid sequence encodes sufficient information for the membrane topology of this crucial gating helix. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

In situ atomic force microscope imaging of supported lipid bilayers

DEFF Research Database (Denmark)

Kaasgaard, Thomas; Leidy, Chad; Ipsen, John Hjorth

2001-01-01

In situ AFM images of phospholipase A/sub 2/ (PLA/sub 2/) hydrolysis of mica-supported one- and two-component lipid bilayers are presented. For one-component DPPC bilayers an enhanced enzymatic activity is observed towards preexisting defects in the bilayer. Phase separation is observed in two-co...

Theory of passive proton conductance in lipid bilayers.

Science.gov (United States)

Nagle, J F

1987-10-01

The large permeability of lipid bilayers to protons compared to other small ions calls for a special proton transport mechanism. At the present time, only mechanisms involving transient hydrogen-bonded chains of water can account for the experimental result that the conductance is nearly independent of pH. Three models involving transient hydrogen-bonded chains are discussed, including an outline of the kinetic calculations that lead to predictions of current versus voltage drop and current versus pH differences. These calculations can be compared to experiment to determine which, if any, of these models pertains to lipid bilayers.

Edge states in gated bilayer-monolayer graphene ribbons and bilayer domain walls

Science.gov (United States)

Mirzakhani, M.; Zarenia, M.; Peeters, F. M.

2018-05-01

Using the effective continuum model, the electron energy spectrum of gated bilayer graphene with a step-like region of decoupled graphene layers at the edge of the sample is studied. Different types of coupled-decoupled interfaces are considered, i.e., zigzag (ZZ) and armchair junctions, which result in significant different propagating states. Two non-valley-polarized conducting edge states are observed for ZZ type, which are mainly located around the ZZ-ended graphene layers. Additionally, we investigated both BA-BA and BA-AB domain walls in the gated bilayer graphene within the continuum approximation. Unlike the BA-BA domain wall, which exhibits gapped insulating behaviour, the domain walls surrounded by different stackings of bilayer regions feature valley-polarized edge states. Our findings are consistent with other theoretical calculations, such as from the tight-binding model and first-principles calculations, and agree with experimental observations.

Discriminating binding and positioning of amphiphiles to lipid bilayers by {sup 1}H NMR

Energy Technology Data Exchange (ETDEWEB)

Evanics, F. [Department of Chemistry, University of Toronto, UTM, 3359 Mississauga Rd. North Mississauga, Ont., L5L 1C6 (Canada); Prosser, R.S. [Department of Chemistry, University of Toronto, UTM, 3359 Mississauga Rd. North Mississauga, Ont., L5L 1C6 (Canada)]. E-mail: sprosser@utm.utoronto.ca

2005-04-04

The binding and positioning in lipid bilayers of three well-known drugs--imipramine, nicotine, and caffeine--have been studied using {sup 1}H NMR. The membrane model system consisted of 'fast-tumbling' lipid bicelles, in which a bilayered lipid domain, composed of the unsaturated lipid, 1,2-dimyristelaidoyl-sn-glycero-3-phosphocholine (DMLPC) was surrounded by a rim of deuterated detergent-like lipids, consisting of 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC-d22). Binding and immersion depth information was obtained by three experiments. (1) {sup 1}H chemical shift perturbations, upon transfer of the amphiphiles from water to a bicelle mixture, were used to estimate regions of the amphiphiles that interact with the membrane. (2) Water contact to resolvable protons was measured through a Nuclear Overhauser Effect (NOE) between water and resolvable drug and lipid resonances. In the case of both lipids and membrane bound drugs, positive NOEs with large cross-relaxation rates were measured for most resonances originating from the membrane hydrophilic region, while negative NOEs were observed predominantly to resonances in the hydrophobic region of the membrane. (3) {sup 1}H NMR measurements of oxygen-induced (paramagnetic) spin-lattice relaxation rates, which are known to increase with membrane immersion depth, were used to corroborate conclusions based on chemical shift perturbations and water-ligand NOEs.

Regulation of membrane protein function by lipid bilayer elasticity-a single molecule technology to measure the bilayer properties experienced by an embedded protein

International Nuclear Information System (INIS)

Lundbaek, Jens August

2006-01-01

Membrane protein function is generally regulated by the molecular composition of the host lipid bilayer. The underlying mechanisms have long remained enigmatic. Some cases involve specific molecular interactions, but very often lipids and other amphiphiles, which are adsorbed to lipid bilayers, regulate a number of structurally unrelated proteins in an apparently non-specific manner. It is well known that changes in the physical properties of a lipid bilayer (e.g., thickness or monolayer spontaneous curvature) can affect the function of an embedded protein. However, the role of such changes, in the general regulation of membrane protein function, is unclear. This is to a large extent due to lack of a generally accepted framework in which to understand the many observations. The present review summarizes studies which have demonstrated that the hydrophobic interactions between a membrane protein and the host lipid bilayer provide an energetic coupling, whereby protein function can be regulated by the bilayer elasticity. The feasibility of this 'hydrophobic coupling mechanism' has been demonstrated using the gramicidin channel, a model membrane protein, in planar lipid bilayers. Using voltage-dependent sodium channels, N-type calcium channels and GABA A receptors, it has been shown that membrane protein function in living cells can be regulated by amphiphile induced changes in bilayer elasticity. Using the gramicidin channel as a molecular force transducer, a nanotechnology to measure the elastic properties experienced by an embedded protein has been developed. A theoretical and technological framework, to study the regulation of membrane protein function by lipid bilayer elasticity, has been established

Protein-lipid interactions: from membrane domains to cellular networks

National Research Council Canada - National Science Library

Tamm, Lukas K

2005-01-01

... membranes is the lipid bilayer. Embedded in the fluid lipid bilayer are proteins of various shapes and traits. This volume illuminates from physical, chemical and biological angles the numerous - mostly quite weak - interactions between lipids, proteins, and proteins and lipids that define the delicate, highly dynamic and yet so stable fabri...

Combined effects of headgroup charge and tail unsaturation of lipids on lateral organization and diffusion of lipids in model biomembranes

International Nuclear Information System (INIS)

Chen Xiao-Jie; Liang Qing

2017-01-01

Lateral organization and dynamics of lipids in plasma membranes are crucial for several cellular processes such as signal transduction across the membrane and still remain elusive. In this paper, using coarse-grained molecular dynamics simulation, we theoretically study the combined effects of headgroup charge and tail unsaturation of lipids on the lateral organization and diffusion of lipids in ternary lipid bilayers. In neutral ternary lipid bilayers composed of saturated lipids, unsaturated lipids, and cholesterols, under the conditions of given temperature and components, the main factor for the phase separation is the unsaturation of unsaturated lipids and the bilayers can be separated into liquid-ordered domains enriched in saturated lipids and cholesterols and liquid-disordered domains enriched in unsaturated lipids. Once the headgroup charge is introduced, the electrostatic repulsion between the negatively charged lipid headgroups will increase the distance between the charged lipids. We find that the lateral organization and diffusion of the lipids in the (partially) charged ternary lipid bilayers are determined by the competition between the headgroup charge and the unsaturation of the unsaturated lipids. In the bilayers containing unsaturated lipids with lower unsaturation, the headgroup charge plays a crucial role in the lateral organization and diffusion of lipids. The headgroup charge may make the lipid domains unstable and even can suppress phase separation of the lipids in some systems. However, in the bilayers containing highly unsaturated lipids, the lateral organization and diffusion of lipids are mainly dominated by the unsaturation of the unsaturated lipids. This work may provide some theoretical insights into understanding the formation of nanosized domains and lateral diffusion of lipids in plasma membranes. (paper)

Formation of 3D cholesterol crystals from 2D nucleation sites in lipid bilayer membranes: implications for atherosclerosis.

Science.gov (United States)

Varsano, Neta; Fargion, Iael; Wolf, Sharon G; Leiserowitz, Leslie; Addadi, Lia

2015-02-04

Atherosclerosis is the major precursor of cardiovascular disease. The formation of cholesterol crystals in atherosclerotic plaques is associated with the onset of acute pathology. The cholesterol crystals induce physical injury in the plaque core, promoting cell apoptosis and triggering an increased inflammatory response. Herein we address the question of how cholesterol crystal formation occurs in atherosclerosis. We demonstrate that three-dimensional (3D) cholesterol crystals can undergo directed nucleation from bilayer membranes containing two-dimensional (2D) cholesterol crystalline domains. We studied crystal formation on supported lipid bilayers loaded with exogenous cholesterol and labeled using a monoclonal antibody that specifically recognizes ordered cholesterol arrays. Our findings show that 3D crystals are formed exclusively on the bilayer regions where there are segregated 2D cholesterol crystalline domains and that they form on the domains. This study has potentially significant implications for our understanding of the crucial step in the mechanism by which atherosclerotic lesions form.

Simulated microgravity impacts the plant plasmalemma lipid bilayer

Science.gov (United States)

Nedukha, Olena; Berkovich, Yuliy A.; Vorobyeva, Tamara; Grakhov, Volodimir; Klimenko, Elena; Zhupanov, Ivan; Jadko, Sergiy

unsaturated fatty acids, that maintains the plasmalemma fluidity in the normal limits, and it may be considered as an adaptive pattern. This assumption was directly confirmed by the data on plasmalemma fluidity in control and under clinorotation defined by electron paramagnetic resonance spectrometer Bruker Elexsys E 580 (Germany). It was in the first established a significant increase in the sterol content under clinorotation. It is of much interest because sterols along with glyco- and phospholipids and mainly saturated fatty acids form “rafts” that are membrane certain domains, where a lipid bilayer is in the dense, highly ordered state. As rafts include the protein complexes, which are necessary for perception and transduction of exogenous signals, stress protection, pathogenesis, vesicular transport also, a significant increase of sterols under clinorotation may indicate the changes in both membrane permeability and protein activity. On the basis of obtained data, the future researches of components of signaling pathways and regulation of certain plasmalemma membranous proteins activity are grounded and planned.

Triglyceride Blisters in Lipid Bilayers: Implications for Lipid Droplet Biogenesis and the Mobile Lipid Signal in Cancer Cell Membranes

DEFF Research Database (Denmark)

Khandelia, Himanshu; Duelund, Lars; Pakkanen, Kirsi Inkeri

2010-01-01

triolein molecules to the bilayer center in the form of a disordered, isotropic, mobile neutral lipid aggregate, at least 17 nm in diameter, which forms spontaneously, and remains stable on at least the microsecond time scale. The results give credence to the hotly debated existence of mobile neutral lipid...... aggregates of unknown function present in malignant cells, and to the early biogenesis of lipid droplets accommodated between the two leaflets of the endoplasmic reticulum membrane. The TO aggregates give the bilayer a blister-like appearance, and will hinder the formation of multi-lamellar phases in model...

Effects of carotenoids on lipid bilayers.

Science.gov (United States)

Johnson, Quentin R; Mostofian, Barmak; Fuente Gomez, Gabriel; Smith, Jeremy C; Cheng, Xiaolin

2018-01-31

Carotenoids have been found to be important in improving the integrity of biomembranes in eukaryotes. However, the molecular details of how carotenoids modulate the physical properties of biomembranes are unknown. To this end, we have conducted a series of molecular dynamics simulations of different biologically-relevant membranes in the presence of carotenoids. The carotenoid effect on the membrane was found to be specific to the identity of the carotenoid and the composition of the membrane itself. Therefore, different classes of carotenoids produce a different effect on the membrane, and different membrane phases are affected differently by carotenoids. It is apparent from our data that carotenoids do trigger the bilayer to become thinner. The mechanism by which this occurs depends on two competing factors, the ability of the lipid tails of opposing monolayers to either (1) compress or (2) interdigitate as the bilayer condenses. Indeed, carotenoids directly influence the physical properties via these two mechanisms, thus compacting the bilayer. However, the degree to which these competing mechanisms are utilized depends on the bilayer phase and the carotenoid identity.

Lipid clustering correlates with membrane curvature as revealed by molecular simulations of complex lipid bilayers.

Directory of Open Access Journals (Sweden)

Heidi Koldsø

2014-10-01

Full Text Available Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP2, in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP2, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins.

Lipid Bilayer Formation on Organic Electronic Materials

KAUST Repository

Zhang, Yi; Wustoni, Shofarul; Savva, Achilleas; Giovannitti, Alexander; McCulloch, Iain; Inal, Sahika

2018-01-01

The lipid bilayer is the elemental structure of cell membrane, forming a stable barrier between the interior and exterior of the cell while hosting membrane proteins that enable selective transport of biologically important compounds and cellular

Binding, folding and insertion of a β-hairpin peptide at a lipid bilayer surface: Influence of electrostatics and lipid tail packing.

Science.gov (United States)

Reid, Keon A; Davis, Caitlin M; Dyer, R Brian; Kindt, James T

2018-03-01

Antimicrobial peptides (AMPs) act as host defenses against microbial pathogens. Here we investigate the interactions of SVS-1 (KVKVKVKV d P l PTKVKVKVK), an engineered AMP and anti-cancer β-hairpin peptide, with lipid bilayers using spectroscopic studies and atomistic molecular dynamics simulations. In agreement with literature reports, simulation and experiment show preferential binding of SVS-1 peptides to anionic over neutral bilayers. Fluorescence and circular dichroism studies of a Trp-substituted SVS-1 analogue indicate, however, that it will bind to a zwitterionic DPPC bilayer under high-curvature conditions and folds into a hairpin. In bilayers formed from a 1:1 mixture of DPPC and anionic DPPG lipids, curvature and lipid fluidity are also observed to promote deeper insertion of the fluorescent peptide. Simulations using the CHARMM C36m force field offer complementary insight into timescales and mechanisms of folding and insertion. SVS-1 simulated at an anionic mixed POPC/POPG bilayer folded into a hairpin over a microsecond, the final stage in folding coinciding with the establishment of contact between the peptide's valine sidechains and the lipid tails through a "flip and dip" mechanism. Partial, transient folding and superficial bilayer contact are seen in simulation of the peptide at a zwitterionic POPC bilayer. Only when external surface tension is applied does the peptide establish lasting contact with the POPC bilayer. Our findings reveal the influence of disruption to lipid headgroup packing (via curvature or surface tension) on the pathway of binding and insertion, highlighting the collaborative effort of electrostatic and hydrophobic interactions on interaction of SVS-1 with lipid bilayers. Copyright © 2017 Elsevier B.V. All rights reserved.

Composition, structure and properties of POPC–triolein mixtures. Evidence of triglyceride domains in phospholipid bilayers

DEFF Research Database (Denmark)

Duelund, Lars; Jensen, Grethe Vestergaard; Hannibal-Bach, Hans Kristian

2013-01-01

We have in this study investigated the composition, structure and spectroscopical properties of multilamellar vesicles composed of a phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and up to 10mol% of triolein (TO), a triglyceride. We found in agreement with previous results...... as vesicular structures containing entrapped water. Bilayer structure of the membranes was supported by small angle X-ray scattering that showed the membranes to form a lamellar phase. Fluorescence spectroscopy with the polarity sensitive dye Nile red revealed, that the LF samples with more than 5mol......% TO contained pure TO domains. These observations are consistent with an earlier MD simulation study by us and our co-workers suggesting triglycerides to be located in lens shaped, blister-like domains between the two lipid bilayer leaflets (Khandelia et al. (2010) [26])....

The cytosolic domain of T-cell receptor ζ associates with membranes in a dynamic equilibrium and deeply penetrates the bilayer.

Science.gov (United States)

Zimmermann, Kerstin; Eells, Rebecca; Heinrich, Frank; Rintoul, Stefanie; Josey, Brian; Shekhar, Prabhanshu; Lösche, Mathias; Stern, Lawrence J

2017-10-27

Interactions between lipid bilayers and the membrane-proximal regions of membrane-associated proteins play important roles in regulating membrane protein structure and function. The T-cell antigen receptor is an assembly of eight single-pass membrane-spanning subunits on the surface of T lymphocytes that initiates cytosolic signaling cascades upon binding antigens presented by MHC-family proteins on antigen-presenting cells. Its ζ-subunit contains multiple cytosolic immunoreceptor tyrosine-based activation motifs involved in signal transduction, and this subunit by itself is sufficient to couple extracellular stimuli to intracellular signaling events. Interactions of the cytosolic domain of ζ (ζ cyt ) with acidic lipids have been implicated in the initiation and regulation of transmembrane signaling. ζ cyt is unstructured in solution. Interaction with acidic phospholipids induces structure, but its disposition when bound to lipid bilayers is controversial. Here, using surface plasmon resonance and neutron reflection, we characterized the interaction of ζ cyt with planar lipid bilayers containing mixtures of acidic and neutral lipids. We observed two binding modes of ζ cyt to the bilayers in dynamic equilibrium: one in which ζ cyt is peripherally associated with lipid headgroups and one in which it penetrates deeply into the bilayer. Such an equilibrium between the peripherally bound and embedded forms of ζ cyt apparently controls accessibility of the immunoreceptor tyrosine-based activation signal transduction pathway. Our results reconcile conflicting findings of the ζ structure reported in previous studies and provide a framework for understanding how lipid interactions regulate motifs to tyrosine kinases and may regulate the T-cell antigen receptor biological activities for this cell-surface receptor system.

Temperature-controlled structure and kinetics of ripple phases in one- and two-component supported lipid bilayers

DEFF Research Database (Denmark)

Kaasgaard, Thomas; Leidy, Chad; Crowe, J.H.

2003-01-01

Temperature-controlled atomic force microscopy (AFM) has been used to visualize and study the structure and kinetics of ripple phases in one-component dipalmitoylphosphaticlylcholine (DPPC) and two-component dimyristoylphosphatidylcholine-distearoylphosphatidylcholine (DMPC-DSPC) lipid bilayers....... The lipid bilayers are mica-supported double bilayers in which ripple-phase formation occurs in the top bilayer. In one-component DPPC lipid bilayers, the stable and metastable ripple phases were observed. In addition, a third ripple structure with approximately twice the wavelength of the metastable...... ripples was seen. From height profiles of the AFM images, estimates of the amplitudes of the different ripple phases are reported. To elucidate the processes of ripple formation and disappearance, a ripple-phase DPPC lipid bilayer was taken through the pretransition in the cooling and the heating...

Electrostatic control of the dynamics of lipid bilayer self-spreading using a nanogap gate

International Nuclear Information System (INIS)

Kashimura, Y; Sumitomo, K; Furukawa, K

2014-01-01

The electrostatic control of lipid bilayer self-spreading was investigated using a device equipped with a nanogap gate. A series of mixtures containing negatively charged and uncharged lipids were employed to tune the charge of a membrane. We found that when a voltage is applied on a lipid bilayer passing through a nanogap, the effect of a voltage application on the dynamics depended largely on the charge of the membrane. For rich charged lipid compositions (>10 mol%), the self-spreading was electrostatically controlled applying an electric field to the nanogap. The origin of the behaviour is the electrostatic trapping of charged lipids. The trapped lipids close the nanogap gate, thus preventing any lipid molecules from passing through it. For poor charged lipid compositions (∼1 mol%), no electrostatic trapping occurred even when a lipid bilayer reached the nanogap. Instead, we observed the cessation of self-spreading after a sufficient post-passage time interval, indicating that the translational flow force of self-spreading overcomes the trapping force. For uncharged lipid compositions, there was no electrostatic trapping throughout the measurement. The results suggest that the lipid charge plays a vital role in the electrostatic control mechanism and allow us to control lipid bilayer formation both spatially and temporally. (paper)

Supported lipid bilayers with controlled curvature via colloidal lithography

DEFF Research Database (Denmark)

Sundh, Maria; Manandhar, Michal; Svedhem, Sofia

2011-01-01

Supported lipid bilayers (SLBs) at surfaces provide a route to quantitatively study molecular interactions with and at lipid membranes via different surface-based analytical techniques. Here, a method to fabricate SLBs with controlled curvatures, in the nanometer regime over large areas, is prese...

Formation of supported lipid bilayers of charged E. coli lipids on modified gold by vesicle fusion

Directory of Open Access Journals (Sweden)

Ileana F. Márquez

2017-01-01

Full Text Available We describe a simple way of fusing E. coli lipid vesicles onto a gold surface. Supported lipid bilayers on metal surfaces are interesting for several reasons: transducing a biological signal to an electric readout, using surface analytical tools such as Surface Plasmon Resonance (SPR, Infrared Reflection Absorption Spectroscopy, Neutron Reflectivity or Electrochemistry. The most widely used method to prepare supported lipid membranes is fusion of preexisting liposomes. It is quite efficient on hydrophilic surfaces such as glass, mica or SiO2, but vesicle fusion on metals and metal oxide surfaces (as gold, titanium oxide or indium tin oxide, remains a challenge, particularly for vesicles containing charged lipids, as is the case of bacterial lipids. We describe a simple method based on modifying the gold surface with a charged mercaptopropionic acid self-assembled monolayer and liposomes partially solubilized with detergent. The formed bilayers were characterized using a Quartz Crystal Microbalance with dissipation (QCM-D and Atomic Force Microscopy (AFM. Some advantages of this protocol are that the stability of the self-assembled monolayer allows for repeated use of the substrate after detergent removal of the bilayer and that the amount of detergent required for optimal fusion can be determined previously using the lipid-detergent solubility curve.

Effect of Membrane Tension on the Electric Field and Dipole Potential of Lipid Bilayer Membrane

Science.gov (United States)

Warshaviak, Dora Toledo; Muellner, Michael J.; Chachisvilis, Mirianas

2011-01-01

The dipole potential of lipid bilayer membrane controls the difference in permeability of the membrane to oppositely charged ions. We have combined molecular dynamics (MD) simulations and experimental studies to determine changes in electric field and electrostatic potential of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid bilayer in response to applied membrane tension. MD simulations based on CHARMM36 force field showed that electrostatic potential of DOPC bilayer decreases by ~45 mV in the physiologically relevant range of membrane tension values (0 to 15 dyn/cm). The electrostatic field exhibits a peak (~0.8×109 V/m) near the water/lipid interface which shifts by 0.9 Å towards the bilayer center at 15 dyn/cm. Maximum membrane tension of 15 dyn/cm caused 6.4% increase in area per lipid, 4.7% decrease in bilayer thickness and 1.4% increase in the volume of the bilayer. Dipole-potential sensitive fluorescent probes were used to detect membrane tension induced changes in DOPC vesicles exposed to osmotic stress. Experiments confirmed that dipole potential of DOPC bilayer decreases at higher membrane tensions. These results are suggestive of a potentially new mechanosensing mechanism by which mechanically induced structural changes in the lipid bilayer membrane could modulate the function of membrane proteins by altering electrostatic interactions and energetics of protein conformational states. PMID:21722624

Collective chain dynamics in lipid bilayers by inelastic x-ray scattering

International Nuclear Information System (INIS)

Weiss, T.M.; Chen, P.-J.; Sinn, H.; Alp, E.E.; Chen, S.-H.; Hwang, H.W.

2003-01-01

We investigated the application of inelastic x-ray scattering (IXS) to lipid bilayers. This technique directly measures the dynamic structure factor S(q,ω) which is the space-time Fourier transform of the electron density correlation function of the measured system. For a multiatomic system, the analysis of S(q,ω) is usually complicated. But for multiple bilayers of lipid, S(q,ω) is dominated by chain-chain correlations within individual bilayers. Thus IXS provides a unique probe for the collective dynamics of lipid chains in a bilayer that cannot be obtained by any other method. IXS of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylcholine + cholesterol at two different concentrations were measured. S(q,ω) was analyzed by three-mode hydrodynamic equations, including a thermal diffusive mode and two propagating acoustic modes. We obtained the dispersion curves for the phonons that represent the collective in-plane excitations of lipid chains. The effect of cholesterol on chain dynamics was detected. Our analysis shows the importance of having a high instrument resolution as well as the requirement of sufficient signal-to-noise ratio to obtain meaningful results from such an IXS experiment. The requirement on signal-to-noise also applies to molecular dynamics simulations.

Development of an automation technique for the establishment of functional lipid bilayer arrays

International Nuclear Information System (INIS)

Hansen, J S; Vogel, J; Geschke, O; Emnéus, J; Nielsen, C H; Perry, M; Vissing, T; Hansen, C R

2009-01-01

In the present work, a technique for establishing multiple black lipid membranes (BLMs) in arrays of micro structured ethylene tetrafluoroethylene (ETFE) films, and supported by a micro porous material was developed. Rectangular 8 × 8 arrays with apertures having diameters of 301 ± 5 µm were fabricated in ETFE Teflon film by laser ablation using a carbon dioxide laser. Multiple lipid membranes could be formed across the micro structured 8 × 8 array ETFE partitions. Success rates for the establishment of cellulose-supported BLMs across the multiple aperture arrays were above 95%. However, the time course of the membrane thinning process was found to vary considerably between multiple aperture bilayer experiments. An airbrush partition pretreatment technique was developed to increase the reproducibility of the multiple lipid bilayers formation during the time course from the establishment of the lipid membranes to the formation of bilayers. The results showed that multiple lipid bilayers could be reproducible formed across the airbrush-pretreated 8 × 8 rectangular arrays. The ionophoric peptide valinomycin was incorporated into established membrane arrays, resulting in ionic currents that could be effectively blocked by tetraethylammonium. This shows that functional bimolecular lipid membranes were established, and furthermore outlines that the established lipid membrane arrays could host functional membrane-spanning molecules

Slaved diffusion in phospholipid bilayers

Science.gov (United States)

Zhang, Liangfang; Granick, Steve

2005-01-01

The translational diffusion of phospholipids in supported fluid bilayers splits into two populations when polyelectrolytes adsorb at incomplete surface coverage. Spatially resolved measurements using fluorescence correlation spectroscopy show that a slow mode, whose magnitude scales inversely with the degree of polymerization of the adsorbate, coexists with a fast mode characteristic of naked lipid diffusion. Inner and outer leaflets of the bilayer are affected nearly equally. Mobility may vary from spot to spot on the membrane surface, despite the lipid composition being the same. This work offers a mechanism to explain how nanosized domains with reduced mobility arise in lipid membranes. PMID:15967988

Dynamic patterns in a supported lipid bilayer driven by standing surface acoustic waves.

Science.gov (United States)

Hennig, Martin; Neumann, Jürgen; Wixforth, Achim; Rädler, Joachim O; Schneider, Matthias F

2009-11-07

In the past decades supported lipid bilayers (SLBs) have been an important tool in order to study the physical properties of biological membranes and cells. So far, controlled manipulation of SLBs is very limited. Here we present a new technology to create lateral patterns in lipid membranes controllable in both space and time. Surface acoustic waves (SAWs) are used to generate lateral standing waves on a piezoelectric substrate which create local "traps" in the lipid bilayer and lead to a lateral modulation in lipid concentration. We demonstrate that pattern formation is reversible and does not affect the integrity of the lipid bilayer as shown by extracting the diffusion constant of fluid membranes. The described method could possibly be used to design switchable interfaces for the lateral transport and organization of membrane bound macromolecules to create dynamic bioarrays and control biofilm formation.

Examining the origins of the hydration force between lipid bilayers using all-atom simulations.

Science.gov (United States)

Gentilcore, Anastasia N; Michaud-Agrawal, Naveen; Crozier, Paul S; Stevens, Mark J; Woolf, Thomas B

2010-05-01

Using 237 all-atom double bilayer simulations, we examined the thermodynamic and structural changes that occur as a phosphatidylcholine lipid bilayer stack is dehydrated. The simulated system represents a micropatch of lipid multilayer systems that are studied experimentally using surface force apparatus, atomic force microscopy and osmotic pressure studies. In these experiments, the hydration level of the system is varied, changing the separation between the bilayers, in order to understand the forces that the bilayers feel as they are brought together. These studies have found a curious, strongly repulsive force when the bilayers are very close to each other, which has been termed the "hydration force," though the origins of this force are not clearly understood. We computationally reproduce this repulsive, relatively free energy change as bilayers come together and make qualitative conclusions as to the enthalpic and entropic origins of the free energy change. This analysis is supported by data showing structural changes in the waters, lipids and salts that have also been seen in experimental work. Increases in solvent ordering as the bilayers are dehydrated are found to be essential in causing the repulsion as the bilayers come together.

Neutron scattering investigations of the lipid bilayer structure pressure dependence

International Nuclear Information System (INIS)

Solovjov, D.V.; Gordelyij, V.Yi.; Gorshkova, Yu.Je.; Yivan'kov, O.Yi.; Koval'ov, Yu.S.; Kuklyin, A.Yi.; Solovjov, D.V.; Bulavyin, L.A.; Yivan'kov, O.Yi.; Nyikolajenko, T.Yu.; Kuklyin, A.Yi.; Gordelyij, V.Yi.; Gordelyij, V.Yi.

2012-01-01

Lipid bilayer structure investigation results obtained with small angle neutron scattering method at the Joint Institute for Nuclear Research IBR-2M nuclear reactor (Dubna, Russia) are presented. Experiment has been performed with small angle neutron scattering spectrometer YuMO, upgraded with the apparatus for performing PV-T measurements on the substance under investigation. D 2 O-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liquid system, presenting the model of natural live membrane, has been taken as the sample for investigations. The lipid bilayer spatial period was measured in experiment along with isothermal compressibility simultaneously at different pressures. It has been shown, that the bilayer structural transition from ripple (wavelike gel-phase) phase to liquid-crystal phase is accompanied with anomalous rise of isothermal compressibility, indicating occurrence of the phase transition.

Recent progress on lipid lateral heterogeneity in plasma membranes: from rafts to submicrometric domains

Science.gov (United States)

Carquin, Mélanie; D'Auria, Ludovic; Pollet, Hélène; Bongarzone, Ernesto R.; Tyteca, Donatienne

2016-01-01

The concept of transient nanometric domains known as lipid rafts has brought interest to reassess the validity of the Singer-Nicholson model of a fluid bilayer for cell membranes. However, this new view is still insufficient to explain the cellular control of surface lipid diversity or membrane deformability. During the past decade, the hypothesis that some lipids form large (submicrometric/mesoscale vs nanometric rafts) and stable (> min vs sec) membrane domains has emerged, largely based on indirect methods. Morphological evidence for stable submicrometric lipid domains, well-accepted for artificial and highly specialized biological membranes, was further reported for a variety of living cells from prokaryotes to yeast and mammalian cells. However, results remained questioned based on limitations of available fluorescent tools, use of poor lipid fixatives, and imaging artifacts due to non-resolved membrane projections. In this review, we will discuss recent evidence generated using powerful and innovative approaches such as lipid-specific toxin fragments that support the existence of submicrometric domains. We will integrate documented mechanisms involved in the formation and maintenance of these domains, and provide a perspective on their relevance on membrane deformability and regulation of membrane protein distribution. PMID:26738447

Separating attoliter-sized compartments using fluid pore-spanning lipid bilayers.

Science.gov (United States)

Lazzara, Thomas D; Carnarius, Christian; Kocun, Marta; Janshoff, Andreas; Steinem, Claudia

2011-09-27

Anodic aluminum oxide (AAO) is a porous material having aligned cylindrical compartments with 55-60 nm diameter pores, and being several micrometers deep. A protocol was developed to generate pore-spanning fluid lipid bilayers separating the attoliter-sized compartments of the nanoporous material from the bulk solution, while preserving the optical transparency of the AAO. The AAO was selectively functionalized by silane chemistry to spread giant unilamellar vesicles (GUVs) resulting in large continuous membrane patches covering the pores. Formation of fluid single lipid bilayers through GUV rupture could be readily observed by fluorescence microscopy and further supported by conservation of membrane surface area, before and after GUV rupture. Fluorescence recovery after photobleaching gave low immobile fractions (5-15%) and lipid diffusion coefficients similar to those found for bilayers on silica. The entrapment of molecules within the porous underlying cylindrical compartments, as well as the exclusion of macromolecules from the nanopores, demonstrate the barrier function of the pore-spanning membranes and could be investigated in three-dimensions using confocal laser scanning fluorescence imaging. © 2011 American Chemical Society

Molecular dynamics simulations of the effects of sodium dodecyl sulfate on lipid bilayer

International Nuclear Information System (INIS)

Xu Bin; Lin Wen-Qiang; Wang Xiao-Gang; Zhou Guo-Quan; Chen Jun-Lang; Zeng Song-wei

2017-01-01

Molecular dynamics simulations have been performed on the fully hydrated lipid bilayer with different concentrations of sodium dodecyl sulfate (SDS). SDS can readily penetrate into the membrane. The insertion of SDS causes a decrease in the bilayer area and increases in the bilayer thickness and lipid tail order, when the fraction of SDS is less than 28%. Through calculating the binding energy, we confirm that the presence of SDS strengthens the interactions among the DPPC lipids, while SDS molecules act as intermedia. Both the strong hydrophilic interactions between sulfate and phosphocholine groups and the hydrophobic interactions between SDS and DPPC hydrocarbon chains contribute to the tight packing and ordered alignment of the lipids. These results are in good agreement with the experimental observations and provide atomic level information that complements the experiments. (paper)

Subterahertz Longitudinal Phonon Modes Propagating in a Lipid Bilayer Immersed in an Aqueous Medium

Science.gov (United States)

Zakhvataev, V. E.

2018-04-01

The properties of subterahertz longitudinal acoustic phonon modes in the hydrophobic region of a lipid bilayer immersed in a compressible viscous aqueous medium are investigated theoretically. An approximate expression is obtained for the Mandelstam-Brillouin components of the dynamic structure factor of a bilayer. The analysis is based on a generalized hydrodynamic model of the "two-dimensional lipid bilayer + three-dimensional fluid medium" system, as well as on known sharp estimates for the frequencies and lifetimes of long-wavelength longitudinal acoustic phonons in a free hydrated lipid bilayer and in water, obtained from inelastic X-ray scattering experiments and molecular dynamics simulations. It is shown that, for characteristic values of the parameters of the membrane system, subterahertz longitudinal phonon-like excitations in the hydrophobic part of the bilayer are underdamped. In this case, the contribution of the viscous flow of the aqueous medium to the damping of a longitudinal membrane mode is small compared with the contribution of the lipid bilayer. Quantitative estimates of the damping ratio agree well with the experimental results for the vibration mode of the enzyme lysozyme in aqueous solution [1]. It is also shown that a coupling between longitudinal phonon modes of the bilayer and relaxation processes in its fluid environment gives rise to an additional peak in the scattering spectrum, which corresponds to a non-propagating mode.

Neutron scattering investigations of the lipid bilayer structure pressure dependence

Directory of Open Access Journals (Sweden)

D. V. Soloviov

2012-03-01

Full Text Available Lipid bilayer structure investigation results obtained with small angle neutron scattering method at the Joint Institute for Nuclear Research IBR-2M nuclear reactor (Dubna, Russia are presented. Experiment has been per-formed with small angle neutron scattering spectrometer YuMO, upgraded with the apparatus for performing P-V-T measurements on the substance under investigation. D2O-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC liquid system, presenting the model of natural live membrane, has been taken as the sample for investiga-tions. The lipid bilayer spatial period was measured in experiment along with isothermal compressibility simulta-neously at different pressures. It has been shown, that the bilayer structural transition from ripple (wavelike gel-phase phase to liquid-crystal phase is accompanied with anomalous rise of isothermal compressibility, indicat-ing occurrence of the phase transition.

Automatable lipid bilayer formation and ion channel measurement using sessile droplets

Energy Technology Data Exchange (ETDEWEB)

Poulos, J L [Librede Inc., Sherman Oaks, CA (United States); Portonovo, S A; Schmidt, J J [Department of Bioengineering, University of California, Los Angeles, Los Angeles (United States); Bang, H, E-mail: schmidt@seas.ucla.ed [School of Mechanical and Aerospace Engineering, Seoul National University (Korea, Republic of)

2010-11-17

Artificial lipid bilayer membranes have been used to reconstitute ion channels for scientific and technological applications. Membrane formation has traditionally involved slow, labor intensive processes best suited to small scale laboratory experimentation. We have recently demonstrated a high throughput method of membrane formation using automated liquid-handling robotics. We describe here the integration of membrane formation and measurement with two methods compatible with automation and high throughput liquid-handling robotics. Both of these methods create artificial lipid bilayers by joining lipid monolayers self-assembled at the interface of aqueous and organic phases using sessile aqueous droplets in contact with a measurement electrode; one using a pin tool, commonly employed in high throughput fluid handling assays, and the other using a positive displacement pipette. Membranes formed with both methods were high quality and supported measurement of ion channels at the single molecule level. Full automation of bilayer production and measurement with the positive displacement pipette was demonstrated by integrating it with a motion control platform.

Fluorescent molecular probes based on excited state prototropism in lipid bilayer membrane

Science.gov (United States)

Mohapatra, Monalisa; Mishra, Ashok K.

2012-03-01

Excited state prototropism (ESPT) is observed in molecules having one or more ionizable protons, whose proton transfer efficiency is different in ground and excited states. The interaction of various ESPT molecules like naphthols and intramolecular ESPT (ESIPT) molecules like hydroxyflavones etc. with different microheterogeneous media have been studied in detail and excited state prototropism as a probe concept has been gaining ground. The fluorescence of different prototropic forms of such molecules, on partitioning to an organized medium like lipid bilayer membrane, often show sensitive response to the local environment with respect to the local structure, physical properties and dynamics. Our recent work using 1-naphthol as an ESPT fluorescent molecular probe has shown that the incorporation of monomeric bile salt molecules into lipid bilayer membranes composed from dipalmitoylphosphatidylcholine (DPPC, a lung surfactant) and dimyristoylphosphatidylcholine (DMPC), in solid gel and liquid crystalline phases, induce appreciable wetting of the bilayer up to the hydrocarbon core region, even at very low (fisetin, an ESIPT molecule having antioxidant properties, in lipid bilayer membrane has been sensitively monitored from its intrinsic fluorescence behaviour.

Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol

Energy Technology Data Exchange (ETDEWEB)

Worcester, D.L.; Hamacher, K.; Kaiser, H.; Kulasekere, R.; Torbet, J. [Univ. of Missouri, Columbia, MO (United States)

1994-12-31

Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer.

Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol

International Nuclear Information System (INIS)

Worcester, D.L.; Hamacher, K.; Kaiser, H.; Kulasekere, R.; Torbet, J.

1994-01-01

Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer

Properties of POPC/POPE supported lipid bilayers modified with hydrophobic quantum dots on polyelectrolyte cushions.

Science.gov (United States)

Kolasinska-Sojka, Marta; Wlodek, Magdalena; Szuwarzynski, Michal; Kereiche, Sami; Kovacik, Lubomir; Warszynski, Piotr

2017-10-01

The formation and properties of supported lipid bilayers (SLB) containing hydrophobic nanoparticles (NP) was studied in relation to underlying cushion obtained from selected polyelectrolyte multilayers. Lipid vesicles were formed from zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) in phosphate buffer (PBS). As hydrophobic nanoparticles - quantum dots (QD) with size of 3.8nm (emission wavelength of 420nm) were used. Polyelectrolyte multilayers (PEM) were constructed by the sequential, i.e., layer-by-layer (LbL) adsorption of alternately charged polyelectrolytes from their solutions. Liposomes and Liposome-QDs complexes were studied with Transmission Cryo-Electron Microscopy (Cryo-TEM) to verify the quality of vesicles and the position of QD within lipid bilayer. Deposition of liposomes and liposomes with quantum dots on polyelectrolyte films was studied in situ using quartz crystal microbalance with dissipation (QCM-D) technique. The fluorescence emission spectra were analyzed for both: suspension of liposomes with nanoparticles and for supported lipid bilayers containing QD on PEM. It was demonstrated that quantum dots are located in the hydrophobic part of lipid bilayer. Moreover, we proved that such QD-modified liposomes formed supported lipid bilayers and their final structure depended on the type of underlying cushion. Copyright © 2017 Elsevier B.V. All rights reserved.

15N and 31P solid-state NMR study of transmembrane domain alignment of M2 protein of influenza A virus in hydrated cylindrical lipid bilayers confined to anodic aluminum oxide nanopores.

Science.gov (United States)

Chekmenev, Eduard Y; Hu, Jun; Gor'kov, Peter L; Brey, William W; Cross, Timothy A; Ruuge, Andres; Smirnov, Alex I

2005-04-01

This communication reports the first example of a high resolution solid-state 15N 2D PISEMA NMR spectrum of a transmembrane peptide aligned using hydrated cylindrical lipid bilayers formed inside nanoporous anodic aluminum oxide (AAO) substrates. The transmembrane domain SSDPLVVA(A-15N)SIIGILHLILWILDRL of M2 protein from influenza A virus was reconstituted in hydrated 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine bilayers that were macroscopically aligned by a conventional micro slide glass support or by the AAO nanoporous substrate. 15N and 31P NMR spectra demonstrate that both the phospholipids and the protein transmembrane domain are uniformly aligned in the nanopores. Importantly, nanoporous AAO substrates may offer several advantages for membrane protein alignment in solid-state NMR studies compared to conventional methods. Specifically, higher thermal conductivity of aluminum oxide is expected to suppress thermal gradients associated with inhomogeneous radio frequency heating. Another important advantage of the nanoporous AAO substrate is its excellent accessibility to the bilayer surface for exposure to solute molecules. Such high accessibility achieved through the substrate nanochannel network could facilitate a wide range of structure-function studies of membrane proteins by solid-state NMR.

Atomic Force Microscope Image Contrast Mechanisms on Supported Lipid Bilayers

OpenAIRE

Schneider, James; Dufrêne, Yves F.; Barger Jr., William R.; Lee, Gil U.

2000-01-01

This work presents a methodology to measure and quantitatively interpret force curves on supported lipid bilayers in water. We then use this method to correlate topographic imaging contrast in atomic force microscopy (AFM) images of phase-separated Langmuir-Blodgett bilayers with imaging load. Force curves collected on pure monolayers of both distearoylphosphatidylethanolamine (DSPE) and monogalactosylethanolamine (MGDG) and dioleoylethanolamine (DOPE) deposited at similar surface pressures o...

Ion dynamics in cationic lipid bilayer systems in saline solutions

DEFF Research Database (Denmark)

Miettinen, Markus S; Gurtovenko, Andrey A; Vattulainen, Ilpo

2009-01-01

Positively charged lipid bilayer systems are a promising class of nonviral vectors for safe and efficient gene and drug delivery. Detailed understanding of these systems is therefore not only of fundamental but also of practical biomedical interest. Here, we study bilayers comprising a binary...... are concluded to be interesting for the physics of the whole membrane, especially considering its interaction dynamics with charged macromolecular surfaces....

Off-lattice model for the phase behavior of lipid-cholesterol bilayers

DEFF Research Database (Denmark)

Nielsen, Morten; Miao, Ling; Ipsen, John Hjorth

1999-01-01

and previous approximate theories have suggested that cholesterol incorporated into lipid bilayers has different microscopic effects on lipid-chain packing and conformations and that cholesterol thereby leads to decoupling of the two ordering processes, manifested by a special equilibrium phase, "liquid...

Cholesterol Perturbs Lipid Bilayers Nonuniversally

International Nuclear Information System (INIS)

Pan Jianjun; Mills, Thalia T.; Tristram-Nagle, Stephanie; Nagle, John F.

2008-01-01

Cholesterol is well known to modulate the physical properties of biomembranes. Using modern x-ray scattering methods, we have studied the effects of cholesterol on the bending modulus K C , the thickness D HH , and the orientational order parameter S xray of lipid bilayers. We find that the effects are different for at least three classes of phospholipids characterized by different numbers of saturated hydrocarbon chains. Most strikingly, cholesterol strongly increases K C when both chains of the phospholipid are fully saturated but not at all when there are two monounsaturated chains

Functional liposomes and supported lipid bilayers: towards the complexity of biological archetypes.

Science.gov (United States)

Berti, Debora; Caminati, Gabriella; Baglioni, Piero

2011-05-21

This perspective paper provides some illustrative examples on the interplay between information gathered on planar supported lipid bilayers (SLB) and unilamellar lipid vesicles (ULV) to get an integrated description of phenomena occurring at the nanoscale that involve locally bilayered structures. Similarities and differences are underlined and critically compared in terms of biomimetic fidelity and instrumental accessibility to structural and dynamical parameters, focusing on some recent reports that either explicitly address this comparison or introducing some studies that separately investigate the same process in SLB and lipid vesicles. Despite the structural similarity on the nanoscale, the different topology implies radically different characterization techniques that have evolved in sectorial and separated approaches. The quest for increasing levels of compositional complexity for bilayered systems should not result in a loss of structural and dynamical control: this is the central challenge of future research in this area, where the integrated approach highlighted in this contribution would enable improved levels of understanding. © The Owner Societies 2011

Lepromatous leprosy patients produce antibodies that recognise non-bilayer lipid arrangements containing mycolic acids

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Isabel Baeza

2012-12-01

Full Text Available Non-bilayer phospholipid arrangements are three-dimensional structures that form when anionic phospholipids with an intermediate structure of the tubular hexagonal phase II are present in a bilayer of lipids. Antibodies that recognise these arrangements have been described in patients with antiphospholipid syndrome and/or systemic lupus erythematosus and in those with preeclampsia; these antibodies have also been documented in an experimental murine model of lupus, in which they are associated with immunopathology. Here, we demonstrate the presence of antibodies against non-bilayer phospholipid arrangements containing mycolic acids in the sera of lepromatous leprosy (LL patients, but not those of healthy volunteers. The presence of antibodies that recognise these non-bilayer lipid arrangements may contribute to the hypergammaglobulinaemia observed in LL patients. We also found IgM and IgG anti-cardiolipin antibodies in 77% of the patients. This positive correlation between the anti-mycolic-non-bilayer arrangements and anti-cardiolipin antibodies suggests that both types of antibodies are produced by a common mechanism, as was demonstrated in the experimental murine model of lupus, in which there was a correlation between the anti-non-bilayer phospholipid arrangements and anti-cardiolipin antibodies. Antibodies to non-bilayer lipid arrangements may represent a previously unrecognised pathogenic mechanism in LL and the detection of these antibodies may be a tool for the early diagnosis of LL patients.

Cholesterol effect on water permeability through DPPC and PSM lipid bilayers: a molecular dynamics study.

Science.gov (United States)

Saito, Hiroaki; Shinoda, Wataru

2011-12-29

Water permeability of two different lipid bilayers of dipalmitoylphosphatidylcholine (DPPC) and palmitoylsphingomyelin (PSM) in the absence and presence of cholesterol (0-50 mol %) have been studied by molecular dynamics simulations to elucidate the molecular mechanism of the reduction in water leakage across the membranes by the addition of cholesterol. An enhanced free energy barrier was observed in these membranes with increased cholesterol concentration, and this was explained by the reduced cavity density around the cholesterol in the hydrophobic membrane core. There was an increase of trans conformers in the hydrophobic lipid chains adjacent to the cholesterol, which reduced the cavity density. The enhanced free energy barrier was found to be the main reason to reduce the water permeability with increased cholesterol concentration. At low cholesterol concentrations the PSM bilayer exhibited a higher free energy barrier than the DPPC bilayer for water permeation, while at greater than 30 mol % of cholesterol the difference became minor. This tendency for the PSM and DPPC bilayers to resemble each other at higher cholesterol concentrations was similar to commonly observed trends in several structural properties, such as order parameters, cross-sectional area per molecule, and cavity density profiles in the hydrophobic regions of bilayer membranes. These results demonstrate that DPPC and PSM bilayers with high cholesterol contents possess similar physical properties, which suggests that the solubility of cholesterol in these lipid bilayers has importance for an understanding of multicomponent lipid membranes with cholesterol. © 2011 American Chemical Society

Physisorbed Polymer-Tethered Lipid Bilayer with Lipopolymer Gradient

Directory of Open Access Journals (Sweden)

Christoph A. Naumann

2012-11-01

Full Text Available Physisorbed polymer-tethered lipid bilayers consisting of phospholipids and lipopolymers represent an attractive planar model membrane platform, in which bilayer fluidity and membrane elastic properties can be regulated through lipopolymer molar concentration. Herein we report a method for the fabrication of such a planar model membrane system with a lateral gradient of lipopolymer density. In addition, a procedure is described, which leads to a sharp boundary between regions of low and high lipopolymer molar concentrations. Resulting gradients and sharp boundaries are visualized on the basis of membrane buckling structures at elevated lipopolymer concentrations using epifluorescence microscopy and atomic force microscopy. Furthermore, results from spot photobleaching experiments are presented, which provide insight into the lipid lateral fluidity in these model membrane architectures. The presented experimental data highlight a planar, solid-supported membrane characterized by fascinating length scale-dependent dynamics and elastic properties with remarkable parallels to those observed in cellular membranes.

Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling

Energy Technology Data Exchange (ETDEWEB)

Pera, H.; Kleijn, J. M.; Leermakers, F. A. M., E-mail: Frans.leermakers@wur.nl [Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6307 HB Wageningen (Netherlands)

2014-02-14

To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus k{sub c} and k{sup ¯} and the preferred monolayer curvature J{sub 0}{sup m}, and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of k{sub c} and the area compression modulus k{sub A} are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for k{sup ¯} and J{sub 0}{sup m} can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both k{sup ¯} and J{sub 0}{sup m} change sign with relevant parameter changes. Although typically k{sup ¯}<0, membranes can form stable cubic phases when the Gaussian bending modulus becomes positive, which occurs with membranes composed of PC lipids with long tails. Similarly, negative monolayer curvatures appear when a small head group such as PE is combined with long lipid tails, which hints towards the stability of inverse hexagonal phases at the cost of the bilayer topology. To prevent the destabilisation of bilayers, PG lipids can be mixed into these PC or PE lipid membranes. Progressive loading of bilayers with PG lipids lead to highly charged membranes, resulting in J{sub 0}{sup m}≫0, especially at low ionic

Position of residues in transmembrane peptides with respect to the lipid bilayer: A combined lipid NOEs and water chemical exchange approach in phospholipid bicelles

International Nuclear Information System (INIS)

Glover, Kerney Jebrell; Whiles, Jennifer A.; Vold, Regitze R.; Melacini, Giuseppe

2002-01-01

The model transmembrane peptide P16 was incorporated into small unaligned phospholipid bicelles, which provide a 'native-like' lipid bilayer compatible with high-resolution solution NMR techniques. Using amide-water chemical exchange and amide-lipid cross-relaxation measurements, the interactions between P16 and bicelles were investigated. Distinctive intermolecular NOE patterns observed in band-selective 2D-NOESY spectra of bicellar solutions with several lipid deuteration schemes indicated that P16 is preferentially interacting with the 'bilayered' region of the bicelle rather than with the rim. Furthermore, when amide-lipid NOEs were combined with amide-water chemical exchange cross-peaks of selectively 15 N-labeled P16 peptides, valuable information was obtained about the position of selected residues relative to the membrane-water interface. Specifically, three main classes were identified. Class I residues lie outside the bilayer and show amide-water exchange cross-peaks but no amide-lipid NOEs. Class II residues reside in the bilayer-water interface and show both amide-water exchange cross-peaks and amide-lipid NOEs. Class III residues are embedded within the hydrophobic core of the membrane and show no amide-water exchange cross-peaks but strong amide-lipid NOEs

A portable lipid bilayer system for environmental sensing with a transmembrane protein.

Directory of Open Access Journals (Sweden)

Ryuji Kawano

Full Text Available This paper describes a portable measurement system for current signals of an ion channel that is composed of a planar lipid bilayer. A stable and reproducible lipid bilayer is formed in outdoor environments by using a droplet contact method with a micropipette. Using this system, we demonstrated that the single-channel recording of a transmembrane protein (alpha-hemolysin was achieved in the field at a high-altitude (∼3623 m. This system would be broadly applicable for obtaining environmental measurements using membrane proteins as a highly sensitive sensor.

Water distribution function across the curved lipid bilayer: SANS study

International Nuclear Information System (INIS)

Kiselev, M.A.; Zemlyanaya, E.V.; Ryabova, N.Y.; Hauss, T.; Dante, S.; Lombardo, D.

2008-01-01

The neutron scattering length density across the membrane is simulated on the basis of fluctuated model of lipid bilayer. The use of a separated form factors method has been applied for the identification of the structural features of the polydispersed unilamellar DMPC vesicle system. The hydration of vesicle is described by sigmoid distribution function of the water molecules. The application of the model to the obtained SANS spectra allow the determination of the main parameters of the system, such as the average vesicle radius (and its polydispersity), the membrane thickness, the thickness of hydrocarbon chain region, the number of water molecules located per lipid molecule, and the phospholipid surface area. Moreover the approach allow the calculation of some relevant parameters connected with the water distribution function across the bilayer system. The main features of the obtained results furnish an explanation of why lipid membrane is easily penetrated by the water molecules of the solution

Irregular bilayer structure in vesicles prepared from Halobacterium cutirubrum lipids

Science.gov (United States)

Lanyi, J. K.

1974-01-01

Fluorescent probes were used to study the structure of the cell envelope of Halobacterium cutirubrum, and, in particular, to explore the effect of the heterogeneity of the lipids in this organism on the structure of the bilayers. The fluorescence polarization of perylene was followed in vesicles of unfractionated lipids and polar lipids as a function of temperature in 3.4 M solutions of NaCl, NaNO3, and KSCN, and it was found that vesicles of unfractionated lipids were more perturbed by chaotropic agents than polar lipids. The dependence of the relaxation times of perylene on temperature was studied in cell envelopes and in vesicles prepared from polar lipids, unfractionated lipids, and mixtures of polar and neutral lipids.

Fluid Phase Lipid Areas and Bilayer Thicknesses of Commonly Used Phosphatidylcholines as a Function of Temperature

International Nuclear Information System (INIS)

Kucerka, Norbert; Nieh, Mu-Ping; Katsaras, John

2011-01-01

The structural parameters of fluid phase bilayers composed of phosphatidylcholines with fully saturated, mixed, and branched fatty acid chains, at several temperatures, have been determined by simultaneously analyzing small-angle neutron and X-ray scattering data. Bilayer parameters, such as area per lipid and overall bilayer thickness have been obtained in conjunction with intrabilayer structural parameters (e.g. hydrocarbon region thickness). The results have allowed us to assess the effect of temperature and hydrocarbon chain composition on bilayer structure. For example, we found that for all lipids there is, not surprisingly, an increase in fatty acid chain trans-gauche isomerization with increasing temperature. Moreover, this increase in trans-gauche isomerization scales with fatty acid chain length in mixed chain lipids. However, in the case of lipids with saturated fatty acid chains, trans-gauche isomerization is increasingly tempered by attractive chain-chain van der Waals interactions with increasing chain length. Finally, our results confirm a strong dependence of lipid chain dynamics as a function of double bond position along fatty acid chains.

Structure and organization of nanosized-inclusion-containing bilayer membranes

Science.gov (United States)

Ren, Chun-Lai; Ma, Yu-Qiang

2009-07-01

Based on a considerable amount of experimental evidence for lateral organization of lipid membranes which share astonishingly similar features in the presence of different inclusions, we use a hybrid self-consistent field theory (SCFT)/density-functional theory (DFT) approach to deal with bilayer membranes embedded by nanosized inclusions and explain experimental findings. Here, the hydrophobic inclusions are simple models of hydrophobic drugs or other nanoparticles for biomedical applications. It is found that lipid/inclusion-rich domains are formed at moderate inclusion concentrations and disappear with the increase in the concentration of inclusions. At high inclusion content, chaining of inclusions occurs due to the effective depletion attraction between inclusions mediated by lipids. Meanwhile, the increase in the concentration of inclusions can also cause thickening of the membrane and the distribution of inclusions undergoes a layering transition from one-layer structure located in the bilayer midplane to two-layer structure arranged into the two leaflets of a bilayer. Our theoretical predictions address the complex interactions between membranes and inclusions suggesting a unifying mechanism which reflects the competition between the conformational entropy of lipids favoring the formation of lipid- and inclusion-rich domains in lipids and the steric repulsion of inclusions leading to the uniform dispersion.

Interaction of Cecropin B with Zwitterionic and Negatively Charged Lipid Bilayers Immobilized at Gold Electrode Surface

International Nuclear Information System (INIS)

Juhaniewicz, Joanna; Szyk-Warszyńska, Lilianna; Warszyński, Piotr; Sęk, Sławomir

2016-01-01

Membranolytic properties of cationic antimicrobial peptide cecropin B were investigated using electrochemical techniques, atomic force microscopy and quartz crystal microbalance with dissipation monitoring. Two types of artificial lipid bilayers supported on gold electrode were used as model systems composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol (Chol) at 7:3 molar ratio and L-α-phosphatidylethanolamine (E. coli) (PE), L-α-phosphatidylglycerol sodium salt (E. coli) (PG) at 8:2 molar ratio. Thus the lipid content was intended to represent either mammalian or bacterial membrane respectively. Model bilayers were exposed to cecropin B at 1 μM concentration and the changes in bilayer structure, permeability and morphology were monitored as a function of time. We have found that cecropin B does not show any pronounced effect on POPC/Chol bilayer, while PE/PG system was strongly affected in the presence of the peptide. This observation suggests that cecropin B shows some selectivity with respect to lipid composition of the membrane. In case of PE/PG membrane, we have observed that peptide action involves electrostatically driven adsorption of the cecropin B at the top of the bilayer with simultaneous fluidization and swelling of the membrane. The latter may facilitate the rearrangement and insertion of the molecules into the core of the lipid bilayer, which leads to further rupture and degradation of the film through formation of mixed peptide-lipid aggregates.

Bilayer/cytoskeleton interactions in lipid-symmetric erythrocytes assessed by a photoactivable phospholipid analogue

International Nuclear Information System (INIS)

Pradhan, D.; Schlegel, R.A.; Williamson, P.

1991-01-01

Two mechanisms have been proposed for maintenance of transbilayer phospholipid asymmetry in the erythrocyte plasma membrane, one involving specific interactions between the aminophospholipids of the inner leaflet of the bilayer and the cytoskeleton, particularly spectrin, and the other involving the aminophospholipid translocase. If the former mechanism is correct, then erythrocytes which have lost their asymmetric distribution of phospholipids should display altered bilayer/cytoskeleton interactions. To test this possibility, normal erythrocytes, erythrocytes from patients with chronic myelogenous leukemia or sickle disease, and lipid-symmetric and -asymmetric erythrocyte ghosts were labeled with the radioactive photoactivable analogue of phosphatidylethanolamine, 2-(2-azido-4-nitrobenzoyl)-1-acyl-sn-glycero-3-phospho[ 14 C] ethanolamine ([ 14 C]AzPE), previously shown to label cytoskeletal proteins from the bilayer. The labeling pattern of cytoskeletal proteins in pathologic erythrocytes and lipid-asymmetric erythrocyte ghosts was indistinguishable from normal erythrocytes, indicating that the probe detects no differences in bilayer/cytoskeleton interactions in these cells. In contrast, in lipid-symmetric erythrocyte ghosts, labeling of bands 4.1 and 4.2 and actin, and to a lesser extent ankyrin, by [ 14 C]AzPE was considerably reduced. Significantly, however, labeling of spectrin was unaltered in the lipid-symmetric cells. These results do not support a model in which spectrin is involved in the maintenance of an asymmetric distribution of phospholipids in erythrocytes

A lipid E-MAP identifies Ubx2 as a critical regulator of lipid saturation and lipid bilayer stress

DEFF Research Database (Denmark)

Surma, Michal A; Klose, Christian; Peng, Debby

2013-01-01

Biological membranes are complex, and the mechanisms underlying their homeostasis are incompletely understood. Here, we present a quantitative genetic interaction map (E-MAP) focused on various aspects of lipid biology, including lipid metabolism, sorting, and trafficking. This E-MAP contains ∼250......,000 negative and positive genetic interaction scores and identifies a molecular crosstalk of protein quality control pathways with lipid bilayer homeostasis. Ubx2p, a component of the endoplasmic-reticulum-associated degradation pathway, surfaces as a key upstream regulator of the essential fatty acid (FA...

Lipid-bilayer-assisted two-dimensional self-assembly of DNA origami nanostructures

Science.gov (United States)

Endo, Masayuki; Sugiyama, Hiroshi

2015-01-01

Self-assembly is a ubiquitous approach to the design and fabrication of novel supermolecular architectures. Here we report a strategy termed ‘lipid-bilayer-assisted self-assembly' that is used to assemble DNA origami nanostructures into two-dimensional lattices. DNA origami structures are electrostatically adsorbed onto a mica-supported zwitterionic lipid bilayer in the presence of divalent cations. We demonstrate that the bilayer-adsorbed origami units are mobile on the surface and self-assembled into large micrometre-sized lattices in their lateral dimensions. Using high-speed atomic force microscopy imaging, a variety of dynamic processes involved in the formation of the lattice, such as fusion, reorganization and defect filling, are successfully visualized. The surface modifiability of the assembled lattice is also demonstrated by in situ decoration with streptavidin molecules. Our approach provides a new strategy for preparing versatile scaffolds for nanofabrication and paves the way for organizing functional nanodevices in a micrometer space. PMID:26310995

Lipid-bilayer-assisted two-dimensional self-assembly of DNA origami nanostructures

Science.gov (United States)

Suzuki, Yuki; Endo, Masayuki; Sugiyama, Hiroshi

2015-08-01

Self-assembly is a ubiquitous approach to the design and fabrication of novel supermolecular architectures. Here we report a strategy termed `lipid-bilayer-assisted self-assembly' that is used to assemble DNA origami nanostructures into two-dimensional lattices. DNA origami structures are electrostatically adsorbed onto a mica-supported zwitterionic lipid bilayer in the presence of divalent cations. We demonstrate that the bilayer-adsorbed origami units are mobile on the surface and self-assembled into large micrometre-sized lattices in their lateral dimensions. Using high-speed atomic force microscopy imaging, a variety of dynamic processes involved in the formation of the lattice, such as fusion, reorganization and defect filling, are successfully visualized. The surface modifiability of the assembled lattice is also demonstrated by in situ decoration with streptavidin molecules. Our approach provides a new strategy for preparing versatile scaffolds for nanofabrication and paves the way for organizing functional nanodevices in a micrometer space.

Lipid Bilayer Composition Affects Transmembrane Protein Orientation and Function

Directory of Open Access Journals (Sweden)

Katie D. Hickey

2011-01-01

Full Text Available Sperm membranes change in structure and composition upon ejaculation to undergo capacitation, a molecular transformation which enables spermatozoa to undergo the acrosome reaction and be capable of fertilization. Changes to the membrane environment including lipid composition, specifically lipid microdomains, may be responsible for enabling capacitation. To study the effect of lipid environment on proteins, liposomes were created using lipids extracted from bull sperm membranes, with or without a protein (Na+ K+-ATPase or -amylase. Protein incorporation, function, and orientation were determined. Fluorescence resonance energy transfer (FRET confirmed protein inclusion in the lipid bilayer, and protein function was confirmed using a colourometric assay of phosphate production from ATP cleavage. In the native lipid liposomes, ATPase was oriented with the subunit facing the outer leaflet, while changing the lipid composition to 50% native lipids and 50% exogenous lipids significantly altered this orientation of Na+ K+-ATPase within the membranes.

The interaction of new piroxicam analogues with lipid bilayers--a calorimetric and fluorescence spectroscopic study.

Science.gov (United States)

Maniewska, Jadwiga; Szczęśniak-Sięga, Berenika; Poła, Andrzej; Sroda-Pomianek, Kamila; Malinka, Wiesław; Michalak, Krystyna

2014-01-01

The purpose of the present paper was to assess the ability of new piroxicam analogues to interact with the lipid bilayers. The results of calorimetric and fluorescence spectroscopic experiments of two new synthesized analogues of piroxicam, named PR17 and PR18 on the phase behavior of phospholipid bilayers and fluorescence quenching of fluorescent probes (Laurdan and Prodan), which molecular location within membranes is known with certainty, are shown in present work. The presented results revealed that, depending on the details of chemical structure, the studied compounds penetrated the lipid bilayers.

The impact of resveratrol in lipid bilayers

DEFF Research Database (Denmark)

Shen, Chen; de Ghellinck, Alexis; Fragneto, Giovanna

The natural antioxidant resveratrol, contained in the skin of red grape and accordingly in their wines, is hold liable for health impacts such as cardiovascular protection and anti-oxidative effect. Clinical trials of resveratrol as prophylactic or even therapeutic drug are ongoing. However, basic...... knowledge on its probable working mechanism is rare. In this biophysical study, neutron reflectometry was used to investigate the direct impact of resveratrol on lipid membranes with solid supported bilayers. When interacting with di- palmitoyl-phosphatidyl-choline (DPPC) bilayers, resveratrol accumulates...... in between the headgroups but is absent in the hydrophobic core. Without a biogenic removal mechanism, the headgroup region may host up to ~25 mol% of resveratrol. The average thickness and the interfacial roughness of the headgroup layer are increased. From the structural results, the average tilting...

Single-component supported lipid bilayers probed using broadband nonlinear optics.

Science.gov (United States)

Olenick, Laura L; Chase, Hilary M; Fu, Li; Zhang, Yun; McGeachy, Alicia C; Dogangun, Merve; Walter, Stephanie R; Wang, Hong-Fei; Geiger, Franz M

2018-01-31

Broadband SFG spectroscopy is shown to offer considerable advantages over scanning systems in terms of signal-to-noise ratios when probing well-formed single-component supported lipid bilayers formed from zwitterionic lipids with PC headgroups. The SFG spectra obtained from bilayers formed from DOPC, POPC, DLPC, DMPC, DPPC and DSPC show a common peak at ∼2980 cm -1 , which is subject to interference between the C-H and the O-H stretches from the aqueous phase, while membranes having transition temperatures above the laboratory temperature produce SFG spectra with at least two additional peaks, one at ∼2920 cm -1 and another at ∼2880 cm -1 . The results validate spectroscopic and structural data from SFG experiments utilizing asymmetric bilayers in which one leaflet differs from the other in the extent of deuteration. Differences in H 2 O-D 2 O exchange experiments reveal that the lineshapes of the broadband SFG spectra are significantly influenced by interference from OH oscillators in the aqueous phase, even when those oscillators are not probed by the incident infrared light in our broadband setup. In the absence of spectral interference from the OH stretches of the solvent, the alkyl chain terminal methyl group of the bilayer is found to be tilted at an angle of 15° to 35° from the surface normal.

Lipid Bilayer – mediated Regulation of Ion Channel Function by Amphiphilic Drugs

DEFF Research Database (Denmark)

Lundbæk, Jens August

2008-01-01

that are transforming it into a subject of quantitative science. It is described how the hydrophobic interactions between a membrane protein and the host lipid bilayer provide the basis for a mechanism, whereby protein function is regulated by the bilayer physical properties. The use of gramicidin channels as single-molecule......Drugs that at pico- to nanomolar concentration regulate ion channel function by high-affi nity binding to their cognate receptor often have a “ secondary pharmacology, ” in which the same molecule at low micromolar concentrations regulates a diversity of membrane proteins in an apparently...... nonspecifi c manner. It has long been suspected that this promiscuous regulation of membrane protein function could be due to changes in the physical properties of the host lipid bilayer, but the underlying mechanisms have been poorly understood. Given that pharmacological research often involves drug...

Saturation recovery EPR spin-labeling method for quantification of lipids in biological membrane domains.

Science.gov (United States)

Mainali, Laxman; Camenisch, Theodore G; Hyde, James S; Subczynski, Witold K

2017-12-01

The presence of integral membrane proteins induces the formation of distinct domains in the lipid bilayer portion of biological membranes. Qualitative application of both continuous wave (CW) and saturation recovery (SR) electron paramagnetic resonance (EPR) spin-labeling methods allowed discrimination of the bulk, boundary, and trapped lipid domains. A recently developed method, which is based on the CW EPR spectra of phospholipid (PL) and cholesterol (Chol) analog spin labels, allows evaluation of the relative amount of PLs (% of total PLs) in the boundary plus trapped lipid domain and the relative amount of Chol (% of total Chol) in the trapped lipid domain [ M. Raguz, L. Mainali, W. J. O'Brien, and W. K. Subczynski (2015), Exp. Eye Res., 140:179-186 ]. Here, a new method is presented that, based on SR EPR spin-labeling, allows quantitative evaluation of the relative amounts of PLs and Chol in the trapped lipid domain of intact membranes. This new method complements the existing one, allowing acquisition of more detailed information about the distribution of lipids between domains in intact membranes. The methodological transition of the SR EPR spin-labeling approach from qualitative to quantitative is demonstrated. The abilities of this method are illustrated for intact cortical and nuclear fiber cell plasma membranes from porcine eye lenses. Statistical analysis (Student's t -test) of the data allowed determination of the separations of mean values above which differences can be treated as statistically significant ( P ≤ 0.05) and can be attributed to sources other than preparation/technique.

Electroporation of Skin Stratum Corneum Lipid Bilayer and Molecular Mechanism of Drug Transport: A Molecular Dynamics Study.

Science.gov (United States)

Gupta, Rakesh; Rai, Beena

2018-04-30

Skin electroporation has been used significantly to increase the drug permeation. However, molecular mechanism, which resulted in enhancement of flux through skin, is still not known. In this study, extensive atomistic molecular dynamics simulation of skin lipids (made up of ceramide (CER), cholesterol (CHOL) and free fatty acid (FFA)) have been performed at various external electric field. We show for the first time the pore formation in the skin lipid bilayer during the electroporation. We show the effect of applied external electrical field on the pore formation dynamics in lipid bilayer of different size and composition. The pore formation and resealing kinetics were different and was found to be highly dependent on the composition of skin lipid bilayer. The pore formation time decreased with increase in the bilayer size. The pore sustaining electric field was found to be in the range of 0.20-0.25 V/nm for equimolar CER, CHOL and FFA lipid bilayer. The skin lipid bilayer (1:1:1), sealed itself within 20 ns after the removal of external electric field. We also present the molecular mechanism of enhancement of drug permeation in the presence of external field as compared to the passive diffusion. The molecular level understanding obtained here could help in optimizing/designing the electroporation experiments for effective drug delivery. For a given skin composition and size of drug molecule, the combination of pore formation time and pore growth model can be used to know aproiri the desired electric field and time for application of electric field.

Neutron reflectivity studies of single lipid bilayers supported on planar substrates

International Nuclear Information System (INIS)

Krueger, S.; Orts, W.J.; Berk, N.F.; Majkrzak, C.F.; Koenig, B.W.

1994-01-01

Neutron reflectivity was used to probe the structure of single phosphatidylcholine (PC) lipid bilayers adsorbed onto a planar silicon surface in an aqueous environment. Fluctuations in the neutron scattering length density profiles perpendicular to the silicon/water interface were determined for different lipids as a function of the hydrocarbon chain length. The lipids were studied in both the gel and liquid crystalline phases by monitoring changes in the specularly-reflected neutron intensity as a function of temperature. Contrast variation of the neutron scattering length density was applied to both the lipid and the solvent. Scattering length density profiles were determined using both model-independent and model-dependent fitting methods. During the reflectivity measurements, a novel experimental set-up was implemented to decrease the incoherent background scattering due to the solvent. Thus, the reflectivity was measured to Q ∼ 0.3 Angstrom -1 , covering up to seven orders of magnitude in reflected intensity, for PC bilayers in D 2 O and silicon-matched (38% D 2 O/62% H 2 O) water. The kinetics of lipid adsorption at the silicon/water interface were also explored by observing changes in the reflectivity at low Q values under silicon-matched water conditions

Molecular Dynamics Simulations of Hydrophilic Pores in Lipid Bilayers

NARCIS (Netherlands)

Leontiadou, Hari; Mark, Alan E.; Marrink, Siewert J.

Hydrophilic pores are formed in peptide free lipid bilayers under mechanical stress. It has been proposed that the transport of ionic species across such membranes is largely determined by the existence of such meta-stable hydrophilic pores. To study the properties of these structures and understand

Semiconductor particle mediated photoelectron transfers in bilayer lipid membranes

International Nuclear Information System (INIS)

Fendler, J.H.; Baral, S.

1989-01-01

This paper discusses semiconductor particles in situ generated on the cis surface of glyceryl monooleate (GMO) bilayer lipid membranes (BLMs), that have been used to mediate photoelectric effects. The presence of semiconductors on the BLM surface is addressed. The observed photoelectric effects are rationalized and presented

Specific Binding of Adamantane Drugs and Direction of their Polar Amines in the Pore of the Influenza M2 Transmembrane Domain in Lipid Bilayers and Dodecylphosphocholine Micelles Determined by NMR Spectroscopy

Science.gov (United States)

Cady, Sarah D.; Wang, Jun; Wu, Yibing; DeGrado, William F.; Hong, Mei

2011-01-01

The transmembrane domain of the influenza M2 protein (M2TM) forms a tetrameric proton channel important for the virus lifecycle. The proton-channel activity is inhibited by amine-containing adamantyl drugs amantadine and rimantadine, which have been shown to bind specifically to the pore of M2TM near Ser31. However, whether the polar amine points to the N- or C-terminus of the channel has not yet been determined. Elucidating the polar group direction will shed light on the mechanism by which drug binding inhibits this proton channel and will facilitate rational design of new inhibitors. In this study, we determine the polar amine direction using M2TM reconstituted in lipid bilayers as well as DPC micelles. 13C-2H rotational-echo double-resonance NMR experiments of 13C-labeled M2TM and methyl-deuterated rimantadine in lipid bilayers showed that the polar amine pointed to the C-terminus of the channel, with the methyl group close to Gly34. Solution NMR experiments of M2TM in dodecylphosphocholine (DPC) micelles indicate that drug binding causes significant chemical shift perturbations of the protein that are very similar to those seen for M2TM and M2(18–60) bound to lipid bilayers. Specific 2H-labeling of the drugs permitted the assignment of drug-protein cross peaks, which indicate that amantadine and rimantadine bind to the pore in the same fashion as for bilayer-bound M2TM. These results strongly suggest that adamantyl inhibition of M2TM is achieved not only by direct physical occlusion of the pore but also by perturbing the equilibrium constant of the proton-sensing residue His37. The reproduction of the pharmacologically relevant specific pore-binding site in DPC micelles, which was not observed with a different detergent, DHPC, underscores the significant influence of the detergent environment on the functional structure of membrane proteins. PMID:21381693

Lipid bilayer-bound conformation of an integral membrane beta barrel protein by multidimensional MAS NMR

International Nuclear Information System (INIS)

Eddy, Matthew T.; Su, Yongchao; Silvers, Robert; Andreas, Loren; Clark, Lindsay; Wagner, Gerhard; Pintacuda, Guido; Emsley, Lyndon; Griffin, Robert G.

2015-01-01

The human voltage dependent anion channel 1 (VDAC) is a 32 kDa β-barrel integral membrane protein that controls the transport of ions across the outer mitochondrial membrane. Despite the determination of VDAC solution and diffraction structures, a structural basis for the mechanism of its function is not yet fully understood. Biophysical studies suggest VDAC requires a lipid bilayer to achieve full function, motivating the need for atomic resolution structural information of VDAC in a membrane environment. Here we report an essential step toward that goal: extensive assignments of backbone and side chain resonances for VDAC in DMPC lipid bilayers via magic angle spinning nuclear magnetic resonance (MAS NMR). VDAC reconstituted into DMPC lipid bilayers spontaneously forms two-dimensional lipid crystals, showing remarkable spectral resolution (0.5–0.3 ppm for 13 C line widths and <0.5 ppm 15 N line widths at 750 MHz). In addition to the benefits of working in a lipid bilayer, several distinct advantages are observed with the lipid crystalline preparation. First, the strong signals and sharp line widths facilitated extensive NMR resonance assignments for an integral membrane β-barrel protein in lipid bilayers by MAS NMR. Second, a large number of residues in loop regions were readily observed and assigned, which can be challenging in detergent-solubilized membrane proteins where loop regions are often not detected due to line broadening from conformational exchange. Third, complete backbone and side chain chemical shift assignments could be obtained for the first 25 residues, which comprise the functionally important N-terminus. The reported assignments allow us to compare predicted torsion angles for VDAC prepared in DMPC 2D lipid crystals, DMPC liposomes, and LDAO-solubilized samples to address the possible effects of the membrane mimetic environment on the conformation of the protein. Concluding, we discuss the strengths and weaknesses of the reported

NIR studies of cholesterol-dependent structural modification of the model lipid bilayer doped with inhalation anesthetics

Science.gov (United States)

Kuć, Marta; Cieślik-Boczula, Katarzyna; Rospenk, Maria

2018-06-01

The influence of cholesterol on the structure of the model lipid bilayers treated with inhalation anesthetics (enflurane, isoflurane, sevoflurane and halothane) was investigated employing near-infrared (NIR) spectroscopy combined with the Principal Component Analysis (PCA). The conformational changes occurring in the hydrophobic area of the lipid bilayers were analyzed using the first overtones of symmetric (2νs) and antisymmetric (2νas) stretching vibrations of the CH2 groups of lipid aliphatic chains. The temperature values of chain-melting phase transition (Tm) of anesthetic-mixed dipalmitoylphosphatidylcholine (DPPC)/cholesterol and dipalmitoylphosphatidylglycerol (DPPG)/cholesterol membranes, which were obtained from the PCA analysis, were compared with cholesterol-free DPPC and DPPG bilayers mixed with inhalation anesthetics.

Lipid bilayers suspended on microfabricated supports

Science.gov (United States)

Ogier, Simon D.; Bushby, Richard J.; Cheng, Yaling; Cox, Tim I.; Evans, Stephen D.; Knowles, Peter F.; Miles, Robert E.; Pattison, Ian

2001-03-01

The plasma membrane, that exists as part of many animal and plant cells, is a regulator for the transport of ions and small molecules across cell boundaries. Two main components involved are the phospholipid bilayer and the transport proteins. This paper details the construction of a micromachined support for bilayers (MSB) as a first step towards the development of highly selective and highly sensitive ion-channel based biosensors. The device consists of a ~100 micrometer hole in a polymeric support above a cavity that can hold ~25 nL of electrolyte. Electrodes attached to the structure allow the resistance of the membranes to be measured using d.c. conductivity. The MSB is made in two halves, using SU8 ultra-thick resist, which are subsequently bonded together to make the final structure. A layer of gold, surrounding the aperture, enables self-assembled monolayers of alkanethiols to be used to make the polymeric structure biocompatible. Lipid membranes have been formed over these holes with resistances comparable with those of natural membranes >10 MOhmcm^2. The ion-channel gramicidin has successfully been incorporated into the bilayer and its activity monitored. It is proposed that this type of device could be used not only for studying membrane transport phenomena but also as part of an ion-channel based biosensor.

Effect of Ceramide Tail Length on the Structure of Model Stratum Corneum Lipid Bilayers.

Science.gov (United States)

Moore, Timothy C; Hartkamp, Remco; Iacovella, Christopher R; Bunge, Annette L; McCabe, Clare

2018-01-09

Lipid bilayers composed of non-hydroxy sphingosine ceramide (CER NS), cholesterol (CHOL), and free fatty acids (FFAs), which are components of the human skin barrier, are studied via molecular dynamics simulations. Since mixtures of these lipids exist in dense gel phases with little molecular mobility at physiological conditions, care must be taken to ensure that the simulations become decorrelated from the initial conditions. Thus, we propose and validate an equilibration protocol based on simulated tempering, in which the simulation takes a random walk through temperature space, allowing the system to break out of metastable configurations and hence become decorrelated from its initial configuration. After validating the equilibration protocol, which we refer to as random-walk molecular dynamics, the effects of the lipid composition and ceramide tail length on bilayer properties are studied. Systems containing pure CER NS, CER NS + CHOL, and CER NS + CHOL + FFA, with the CER NS fatty acid tail length varied within each CER NS-CHOL-FFA composition, are simulated. The bilayer thickness is found to depend on the structure of the center of the bilayer, which arises as a result of the tail-length asymmetry between the lipids studied. The hydrogen bonding between the lipid headgroups and with water is found to change with the overall lipid composition, but is mostly independent of the CER fatty acid tail length. Subtle differences in the lateral packing of the lipid tails are also found as a function of CER tail length. Overall, these results provide insight into the experimentally observed trend of altered barrier properties in skin systems where there are more CERs with shorter tails present. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Maximally asymmetric transbilayer distribution of anionic lipids alters the structure and interaction with lipids of an amyloidogenic protein dimer bound to the membrane surface.

Science.gov (United States)

Cheng, Sara Y; Chou, George; Buie, Creighton; Vaughn, Mark W; Compton, Campbell; Cheng, Kwan H

2016-03-01

We used molecular dynamics simulations to explore the effects of asymmetric transbilayer distribution of anionic phosphatidylserine (PS) lipids on the structure of a protein on the membrane surface and subsequent protein-lipid interactions. Our simulation systems consisted of an amyloidogenic, beta-sheet rich dimeric protein (D42) absorbed to the phosphatidylcholine (PC) leaflet, or protein-contact PC leaflet, of two membrane systems: a single-component PC bilayer and double PC/PS bilayers. The latter comprised of a stable but asymmetric transbilayer distribution of PS in the presence of counterions, with a 1-component PC leaflet coupled to a 1-component PS leaflet in each bilayer. The maximally asymmetric PC/PS bilayer had a non-zero transmembrane potential (TMP) difference and higher lipid order packing, whereas the symmetric PC bilayer had a zero TMP difference and lower lipid order packing under physiologically relevant conditions. Analysis of the adsorbed protein structures revealed weaker protein binding, more folding in the N-terminal domain, more aggregation of the N- and C-terminal domains and larger tilt angle of D42 on the PC leaflet surface of the PC/PS bilayer versus the PC bilayer. Also, analysis of protein-induced membrane structural disruption revealed more localized bilayer thinning in the PC/PS versus PC bilayer. Although the electric field profile in the non-protein-contact PS leaflet of the PC/PS bilayer differed significantly from that in the non-protein-contact PC leaflet of the PC bilayer, no significant difference in the electric field profile in the protein-contact PC leaflet of either bilayer was evident. We speculate that lipid packing has a larger effect on the surface adsorbed protein structure than the electric field for a maximally asymmetric PC/PS bilayer. Our results support the mechanism that the higher lipid packing in a lipid leaflet promotes stronger protein-protein but weaker protein-lipid interactions for a dimeric protein on

Theory of phase equilibria and critical mixing points in binary lipid bilayers

DEFF Research Database (Denmark)

Risbo, Jens; Sperotto, Maria Maddalena; Mouritsen, Ole G.

1995-01-01

the transition is discussed in terms of the molecular properties of the lipid acyl chains. The results of the numerical model study are expected to have consequences for the interpretation of experimental measurements on lipid bilayer systems in terms of phase diagrams. (C) 1995 American Institute of Physics....

Determinants of sodium and calcium adsorption onto neutral lipid bilayers

Czech Academy of Sciences Publication Activity Database

Javanainen, M.; Melcrová, Adéla; Magarkar, Aniket; Jurkiewicz, Piotr; Hof, Martin; Jungwirth, Pavel; Martinez-Seara, Hector

2017-01-01

Roč. 46, Suppl 1 (2017), S121 ISSN 0175-7571. [IUPAB congress /19./ and EBSA congress /11./. 16.07.2017-20.07.2017, Edinburgh] Institutional support: RVO:61388963 ; RVO:61388955 Keywords : sodium * calcium * lipid bilayer Subject RIV: BO - Biophysics

Porous Materials to Support Bilayer Lipid Membranes for Ion Channel Biosensors

Directory of Open Access Journals (Sweden)

Thai Phung

2011-01-01

Full Text Available To identify materials suitable as membrane supports for ion channel biosensors, six filter materials of varying hydrophobicity, tortuosity, and thickness were examined for their ability to support bilayer lipid membranes as determined by electrical impedance spectroscopy. Bilayers supported by hydrophobic materials (PTFE, polycarbonate, nylon, and silanised silver had optimal resistance (14–19 GΩ and capacitance (0.8–1.6 μF values whereas those with low hydrophobicity did not form BLMs (PVDF or were short-lived (unsilanised silver. The ability of ion channels to function in BLMs was assessed using a method recently reported to improve the efficiency of proteoliposome incorporation into PTFE-supported bilayers. Voltage-gated sodium channel activation by veratridine and inhibition by saxitoxin showed activity for PTFE, nylon, and silanised silver, but not polycarbonate. Bilayers on thicker, more tortuous, and hydrophobic materials produced higher current levels. Bilayers that self-assembled on PTFE filters were the longest lived and produced the most channel activity using this method.

Surface functionalization of a polymeric lipid bilayer for coupling a model biological membrane with molecules, cells, and microstructures.

Science.gov (United States)

Morigaki, Kenichi; Mizutani, Kazuyuki; Saito, Makoto; Okazaki, Takashi; Nakajima, Yoshihiro; Tatsu, Yoshiro; Imaishi, Hiromasa

2013-02-26

We describe a stable and functional model biological membrane based on a polymerized lipid bilayer with a chemically modified surface. A polymerized lipid bilayer was formed from a mixture of two diacetylene-containing phospholipids, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC) and 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphoethanolamine (DiynePE). DiynePC formed a stable bilayer structure, whereas the ethanolamine headgroup of DiynePE enabled functional molecules to be grafted onto the membrane surface. Copolymerization of DiynePC and DiynePE resulted in a robust bilayer. Functionalization of the polymeric bilayer provided a route to a robust and biomimetic surface that can be linked with biomolecules, cells, and three-dimensional (3D) microstructures. Biotin and peptides were grafted onto the polymeric bilayer for attaching streptavidin and cultured mammalian cells by molecular recognition, respectively. Nonspecific adsorption of proteins and cells on polymeric bilayers was minimum. DiynePE was also used to attach a microstructure made of an elastomer (polydimethylsiloxan: PDMS) onto the membrane, forming a confined aqueous solution between the two surfaces. The microcompartment enabled us to assay the activity of a membrane-bound enzyme (cyochrome P450). Natural (fluid) lipid bilayers were incorporated together with membrane-bound proteins by lithographically polymerizing DiynePC/DiynePE bilayers. The hybrid membrane of functionalized polymeric bilayers and fluid bilayers offers a novel platform for a wide range of biomedical applications including biosensor, bioassay, cell culture, and cell-based assay.

Regulation of membrane protein function by lipid bilayer elasticity—a single molecule technology to measure the bilayer properties experienced by an embedded protein

DEFF Research Database (Denmark)

Lundbæk, Jens August

2008-01-01

, regulate a number of structurally unrelated proteins in an apparently non-specific manner. It is well known that changes in the physical properties of a lipid bilayer (e.g., thickness or monolayer spontaneous curvature) can affect the function of an embedded protein. However, the role of such changes......-dependent sodium channels, N-type calcium channels and GABAA receptors, it has been shown that membrane protein function in living cells can be regulated by amphiphile induced changes in bilayer elasticity. Using the gramicidin channel as a molecular force transducer, a nanotechnology to measure the elastic...... properties experienced by an embedded protein has been developed. A theoretical and technological framework, to study the regulation of membrane protein function by lipid bilayer elasticity, has been established....

Neutron reflectivity studies of single lipid bilayers supported on planar substrates

Energy Technology Data Exchange (ETDEWEB)

Krueger, S.; Orts, W.J.; Berk, N.F.; Majkrzak, C.F. [National Inst. of Standards and Technology, Gaithersburg, MD (United States); Koenig, B.W. [National Inst. of Health, Bethesda, MD (United States)

1994-12-31

Neutron reflectivity was used to probe the structure of single phosphatidylcholine (PC) lipid bilayers adsorbed onto a planar silicon surface in an aqueous environment. Fluctuations in the neutron scattering length density profiles perpendicular to the silicon/water interface were determined for different lipids as a function of the hydrocarbon chain length. The lipids were studied in both the gel and liquid crystalline phases by monitoring changes in the specularly-reflected neutron intensity as a function of temperature. Contrast variation of the neutron scattering length density was applied to both the lipid and the solvent. Scattering length density profiles were determined using both model-independent and model-dependent fitting methods. During the reflectivity measurements, a novel experimental set-up was implemented to decrease the incoherent background scattering due to the solvent. Thus, the reflectivity was measured to Q {approx} 0.3{Angstrom}{sup -1}, covering up to seven orders of magnitude in reflected intensity, for PC bilayers in D{sub 2}O and silicon-matched (38% D{sub 2}O/62% H{sub 2}O) water. The kinetics of lipid adsorption at the silicon/water interface were also explored by observing changes in the reflectivity at low Q values under silicon-matched water conditions.

Probing topology and dynamics of the second transmembrane domain (M2δ) of the acetyl choline receptor using magnetically aligned lipid bilayers (bicelles) and EPR spectroscopy.

Science.gov (United States)

Sahu, Indra D; Mayo, Daniel J; Subbaraman, Nidhi; Inbaraj, Johnson J; McCarrick, Robert M; Lorigan, Gary A

2017-08-01

Characterizing membrane protein structure and dynamics in the lipid bilayer membrane is very important but experimentally challenging. EPR spectroscopy offers a unique set of techniques to investigate a membrane protein structure, dynamics, topology, and distance constraints in lipid bilayers. Previously our lab demonstrated the use of magnetically aligned phospholipid bilayers (bicelles) for probing topology and dynamics of the membrane peptide M2δ of the acetyl choline receptor (AchR) as a proof of concept. In this study, magnetically aligned phospholipid bilayers and rigid spin labels were further utilized to provide improved dynamic information and topology of M2δ peptide. Seven TOAC-labeled AchR M2δ peptides were synthesized to demonstrate the utility of a multi-labeling amino acid substitution alignment strategy. Our data revealed the helical tilts to be 11°, 17°, 9°, 17°, 16°, 11°, 9°±4° for residues I7TOAC, Q13TOAC, A14TOAC, V15TOAC, C16TOAC, L17TOAC, and L18TOAC, respectively. The average helical tilt of the M2δ peptide was determined to be ∼13°. This study also revealed that the TOAC labels were attached to the M2δ peptide with different dynamics suggesting that the sites towards the C-terminal end are more rigid when compared to the sites towards the N-terminus. The dynamics of the TOAC labeled sites were more resolved in the aligned samples when compared to the randomly disordered samples. This study highlights the use of magnetically aligned lipid bilayer EPR technique to determine a more accurate helical tilt and more resolved local dynamics of AchR M2δ peptide. Copyright © 2017 Elsevier B.V. All rights reserved.

Affinity of four polar neurotransmitters for lipid bilayer membranes

DEFF Research Database (Denmark)

Wang, Chunhua; Ye, Fengbin; Valardez, Gustavo F.

2011-01-01

. The simulations suggest that this attraction mainly relies on electrostatic interactions of the amino group of the neurotransmitter and the lipid phosphate. We conclude that moderate attraction to lipid membranes occurs for some polar neurotransmitters and hence that one premise for a theory of bilayer-mediated......Weak interactions of neurotransmitters and the lipid matrix in the synaptic membrane have been hypothesized to play a role in synaptic transmission of nerve signals, particularly with respect to receptor desensitization (Cantor, R. S. Biochemistry 2003, 42, 11891). The strength of such interactions......, however, was not measured, and this is an obvious impediment for further evaluation and understanding of a possible role for desensitization. We have used dialysis equilibrium to directly measure the net affinity of selected neurotransmitters for lipid membranes and analyzed this affinity data...

Vesicle fusion observed by content transfer across a tethered lipid bilayer.

Science.gov (United States)

Rawle, Robert J; van Lengerich, Bettina; Chung, Minsub; Bendix, Poul Martin; Boxer, Steven G

2011-10-19

Synaptic transmission is achieved by exocytosis of small, synaptic vesicles containing neurotransmitters across the plasma membrane. Here, we use a DNA-tethered freestanding bilayer as a target architecture that allows observation of content transfer of individual vesicles across the tethered planar bilayer. Tethering and fusion are mediated by hybridization of complementary DNA-lipid conjugates inserted into the two membranes, and content transfer is monitored by the dequenching of an aqueous content dye. By analyzing the diffusion profile of the aqueous dye after vesicle fusion, we are able to distinguish content transfer across the tethered bilayer patch from vesicle leakage above the patch. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Quantifying the Relationship Between Curvature and Electric Potential in Lipid Bilayers

DEFF Research Database (Denmark)

Bruhn, Dennis Skjøth; Lomholt, Michael Andersen; Khandelia, Himanshu

2016-01-01

Cellular membranes mediate vital cellular processes by being subject to curvature and transmembrane electrical potentials. Here we build upon the existing theory for flexoelectricity in liquid crystals to quantify the coupling between lipid bilayer curvature and membrane potentials. Using molecular...... dynamics simulations, we show that head group dipole moments, the lateral pressure profile across the bilayer and spontaneous curvature all systematically change with increasing membrane potentials. In particu- lar, there is a linear dependence between the bending moment (the product of bending rigidity...

Lipid bilayer regulation of membrane protein function: gramicidin channels as molecular force probes

DEFF Research Database (Denmark)

Lundbæk, Jens August; Collingwood, S.A.; Ingolfsson, H.I.

2010-01-01

with collective physical properties (e.g. thickness, intrinsic monolayer curvature or elastic moduli). Studies in physico-chemical model systems have demonstrated that changes in bilayer physical properties can regulate membrane protein function by altering the energetic cost of the bilayer deformation associated...... with a protein conformational change. This type of regulation is well characterized, and its mechanistic elucidation is an interdisciplinary field bordering on physics, chemistry and biology. Changes in lipid composition that alter bilayer physical properties (including cholesterol, polyunsaturated fatty acids...... channels as molecular force probes for studying this mechanism, with a unique ability to discriminate between consequences of changes in monolayer curvature and bilayer elastic moduli....

Lipid-protein interactions in plasma membranes of fiber cells isolated from the human eye lens.

Science.gov (United States)

Raguz, Marija; Mainali, Laxman; O'Brien, William J; Subczynski, Witold K

2014-03-01

The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali, L., Raguz, M., O'Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

Influence of natural organic matter (NOM) coatings on nanoparticle adsorption onto supported lipid bilayers.

Science.gov (United States)

Bo, Zhang; Avsar, Saziye Yorulmaz; Corliss, Michael K; Chung, Minsub; Cho, Nam-Joon

2017-10-05

As the worldwide usage of nanoparticles in commercial products continues to increase, there is growing concern about the environmental risks that nanoparticles pose to biological systems, including potential damage to cellular membranes. A detailed understanding of how different types of nanoparticles behave in environmentally relevant conditions is imperative for predicting and mitigating potential membrane-associated toxicities. Herein, we investigated the adsorption of two popular nanoparticles (silver and buckminsterfullerene) onto biomimetic supported lipid bilayers of varying membrane charge (positive and negative). The quartz crystal microbalance-dissipation (QCM-D) measurement technique was employed to track the adsorption kinetics. Particular attention was focused on understanding how natural organic matter (NOM) coatings affect nanoparticle-bilayer interactions. Both types of nanoparticles preferentially adsorbed onto the positively charged bilayers, although NOM coatings on the nanoparticle and lipid bilayer surfaces could either inhibit or promote adsorption in certain electrolyte conditions. While past findings showed that NOM coatings inhibit membrane adhesion, our findings demonstrate that the effects of NOM coatings are more nuanced depending on the type of nanoparticle and electrolyte condition. Taken together, the results demonstrate that NOM coatings can modulate the lipid membrane interactions of various nanoparticles, suggesting a possible way to improve the environmental safety of nanoparticles. Copyright © 2017 Elsevier B.V. All rights reserved.

Differential dynamic and structural behavior of lipid-cholesterol domains in model membranes.

Directory of Open Access Journals (Sweden)

Luis F Aguilar

Full Text Available Changes in the cholesterol (Chol content of biological membranes are known to alter the physicochemical properties of the lipid lamella and consequently the function of membrane-associated enzymes. To characterize these changes, we used steady-state and time resolved fluorescence spectroscopy and two photon-excitation microscopy techniques. The membrane systems were chosen according to the techniques that were used: large unilamellar vesicles (LUVs for cuvette and giant unilamellar vesicles (GUVs for microscopy measurements; they were prepared from dipalmitoyl phosphatidylcholine (DPPC and dioctadecyl phosphatidylcholine (DOPC in mixtures that are well known to form lipid domains. Two fluorescent probes, which insert into different regions of the bilayer, were selected: 1,6-diphenyl-1,3,5-hexatriene (DPH was located at the deep hydrophobic core of the acyl chain regions and 2-dimethylamino-6-lauroylnaphthalene (Laurdan at the hydrophilic-hydrophobic membrane interface. Our spectroscopy results show that (i the changes induced by cholesterol in the deep hydrophobic phospholipid acyl chain domain are different from the ones observed in the superficial region of the hydrophilic-hydrophobic interface, and these changes depend on the state of the lamella and (ii the incorporation of cholesterol into the lamella induces an increase in the orientation dynamics in the deep region of the phospholipid acyl chains with a corresponding decrease in the orientation at the region close to the polar lipid headgroups. The microscopy data from DOPC/DPPC/Chol GUVs using Laurdan generalized polarization (Laurdan GP suggest that a high cholesterol content in the bilayer weakens the stability of the water hydrogen bond network and hence the stability of the liquid-ordered phase (Lo.

Direct visualization of lipid domains in human skin stratum corneum's lipid membranes

DEFF Research Database (Denmark)

Plasencia, I; Norlen, Lars; Bagatolli, Luis

2007-01-01

scanning calorimetry, fluorescence spectroscopy, and two-photon excitation and laser scanning confocal fluorescence microscopy. Here we show that hydrated bilayers of human skin stratum corneum lipids express a giant sponge-like morphology with dimensions corresponding to the global three......-dimensional morphology of the stratum corneum extracellular space. These structures can be directly visualized using the aforementioned fluorescence microscopy techniques. At skin physiological temperatures (28 degrees C-32 degrees C), the phase state of these hydrated bilayers correspond microscopically (radial...

L-tryptophan-induced electron transport across supported lipid bilayers: an alkyl-chain tilt-angle, and bilayer-symmetry dependence.

Science.gov (United States)

Sarangi, Nirod Kumar; Patnaik, Archita

2012-12-21

Molecular orientation-dependent electron transport across supported 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers (SLBs) on semiconducting indium tin oxide (ITO) is reported with an aim towards potential nanobiotechnological applications. A bifunctional strategy is adopted to form symmetric and asymmetric bilayers of DPPC that interact with L-tryptophan, and are analyzed by surface manometry and atomic force microscopy. Polarization-dependent real-time Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) analysis of these SLBs reveals electrostatic, hydrogen-bonding, and cation-π interactions between the polar head groups of the lipid and the indole side chains. Consequently, a molecular tilt arises from the effective interface dipole, facilitating electron transport across the ITO-anchored SLBs in the presence of an internal Fe(CN)(6)(4-/3-) redox probe. The incorporation of tryptophan enhances the voltammetric features of the SLBs. The estimated electron-transfer rate constants for symmetric and asymmetric bilayers (k(s) = 2.0×10(-2) and 2.8×10(-2) s(-1)) across the two-dimensional (2D) ordered DPPC/tryptophan SLBs are higher compared to pure DPPC SLBs (k(s) = 3.2×10(-3) and 3.9×10(-3) s(-1)). In addition, they are molecular tilt-dependent, as it is the case with the standard apparent rate constants k(app)(0), estimated from electrochemical impedance spectroscopy and bipotentiostatic experiments with a Pt ultramicroelectrode. Lower magnitudes of k(s) and k(app)(0) imply that electrochemical reactions across the ITO-SLB electrodes are kinetically limited and consequently governed by electron tunneling across the SLBs. Standard theoretical rate constants (k(th)(0)) accrued upon electron tunneling comply with the potential-independent electron-tunneling coefficient β = 0.15 Å(-1). Insulator-semiconductor transitions moving from a liquid-expanded to a condensed 2D-phase state of the SLBs are noted, adding a new dimension

Steady-state oxidation of cholesterol catalyzed by cholesterol oxidase in lipid bilayer membranes on platinum electrodes

International Nuclear Information System (INIS)

Bokoch, Michael P.; Devadoss, Anando; Palencsar, Mariela S.; Burgess, James D.

2004-01-01

Cholesterol oxidase is immobilized in electrode-supported lipid bilayer membranes. Platinum electrodes are initially modified with a self-assembled monolayer of thiolipid. A vesicle fusion method is used to deposit an outer leaflet of phospholipids onto the thiolipid monolayer forming a thiolipid/lipid bilayer membrane on the electrode surface. Cholesterol oxidase spontaneously inserts into the electrode-supported lipid bilayer membrane from solution and is consequently immobilized to the electrode surface. Cholesterol partitions into the membrane from buffer solutions containing cyclodextrin. Cholesterol oxidase catalyzes the oxidation of cholesterol by molecular oxygen, forming hydrogen peroxide as a product. Amperometric detection of hydrogen peroxide for continuous solution flow experiments are presented, where flow was alternated between cholesterol solution and buffer containing no cholesterol. Steady-state anodic currents were observed during exposures of cholesterol solutions ranging in concentration from 10 to 1000 μM. These data are consistent with the Michaelis-Menten kinetic model for oxidation of cholesterol as catalyzed by cholesterol oxidase immobilized in the lipid bilayer membrane. The cholesterol detection limit is below 1 μM for cholesterol solution prepared in buffered cyclodextrin. The response of the electrodes to low density lipoprotein solutions is increased upon addition of cyclodextrin. Evidence for adsorption of low density lipoprotein to the electrode surface is presented

Phase behavior of supported lipid bilayers: A systematic study by coarse-grained molecular dynamics simulations

DEFF Research Database (Denmark)

Poursoroush, Asma; Sperotto, Maria Maddalena; Laradji, Mohamed

2017-01-01

Solid-supported lipid bilayers are utilized by experimental scientists as models for biological membranes because of their stability. However, compared to free standing bilayers, their close proximity to the substrate may affect their phase behavior. As this is still poorly understood, and few co...

SANS study of the unilamellar DMPC vesicles. The fluctuation model of lipid bilayer

International Nuclear Information System (INIS)

Kiselev, M.A.; Zemlyanaya, E.V.; Vinod, A.

2003-01-01

On the basis of the separated form-factors model, parameters of the polydispersed unilamellar DMPC vesicle population are analyzed. The neutron scattering length density across the membrane is simulated on the basis of fluctuated model of lipid bilayer. The hydration of vesicle is described by sigmoid distribution function of the water molecules. The results of fitting of the experimental data obtained at the small angle spectrometer SANS-I, PSI (Switzerland) are: average vesicle radius 272±0.4 Armstrong, polydispersity of the radius 27 %, membrane thickness 50.6± Armstrong, thickness of hydrocarbon chain region 21.4±2.8 Armstrong, number of water molecules located per lipid molecule 13±1, and DMPC surface area 59±2 Armstrong 2 . The calculated water distribution function across the bilayer directly explains why lipid membrane is easy penetrated by water molecules

Cluster Formation of Polyphilic Molecules Solvated in a DPPC Bilayer

Directory of Open Access Journals (Sweden)

Xiang-Yang Guo

2017-10-01

Full Text Available We analyse the initial stages of cluster formation of polyphilic additive molecules which are solvated in a dipalmitoylphosphatidylcholine (DPPC lipid bilayer. Our polyphilic molecules comprise an aromatic (trans-bilayer core domain with (out-of-bilayer glycerol terminations, complemented with a fluorophilic and an alkyl side chain, both of which are confined within the aliphatic segment of the bilayer. Large-scale molecular dynamics simulations (1 μ s total duration of a set of six of such polyphilic additives reveal the initial steps towards supramolecular aggregation induced by the specific philicity properties of the molecules. For our intermediate system size of six polyphiles, the transient but recurrent formation of a trimer is observed on a characteristic timescale of about 100 ns. The alkane/perfluoroalkane side chains show a very distinct conformational distribution inside the bilayer thanks to their different philicity, despite their identical anchoring in the trans-bilayer segment of the polyphile. The diffusive mobility of the polyphilic additives is about the same as that of the surrounding lipids, although it crosses both bilayer leaflets and tends to self-associate.

Ripple formation in unilamellar-supported lipid bilayer revealed by FRAPP.

Science.gov (United States)

Harb, Frédéric; Simon, Anne; Tinland, Bernard

2013-12-01

The mechanisms of formation and conditions of the existence of the ripple phase are fundamental thermodynamic questions with practical implications for medicine and pharmaceuticals. We reveal a new case of ripple formation occurring in unilamellar-supported bilayers in water, which results solely from the bilayer/support interaction, without using lipid mixtures or specific ions. This ripple phase is detected by FRAPP using diffusion coefficient measurements as a function of temperature: a diffusivity plateau is observed. It occurs in the same temperature range where ripple phase existence has been observed using other methods. When AFM experiments are performed in the appropriate temperature range the ripple phase is confirmed.

Interaction of Melittin with Negatively Charged Lipid Bilayers Supported on Gold Electrodes

International Nuclear Information System (INIS)

Juhaniewicz, Joanna; Sek, Slawomir

2016-01-01

ABSTRACT: The interactions of melittin, a cationic antimicrobial peptide, with model lipid membranes consisting of negatively charged phospholipids: 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) or 1,2-dimyristoyl-sn-glycero-3-phosphoserine (DMPS) were investigated using electrochemical techniques and atomic force microscopy. Lipid bilayers were deposited on gold electrodes using a combination of Langmuir-Blodgett and Langmuir-Schaefer methods and the resulting membranes established a barrier for electron transfer between the electrode and the redox probe in the solution. After exposure to melittin, the blocking properties of the membranes were monitored using cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that after treatment with peptide, the charge transfer through lipid bilayer is initially strongly inhibited. However, after longer exposure to melittin, the structure of the lipid film becomes less compact and the electrode reactions are facilitated due to the presence of numerous defect sites exposing bare substrate. We have assumed that such behavior reflects initial adsorption of melittin on top of the membrane and its further insertion which leads to formation of the pores or partial micellization of the lipid film. AFM imaging revealed that the exposure to 10 μM melittin solution induces significant structural changes in DMPG and DMPS membranes. However, melittin seems to affect their organization in a different manner. DMPG film appears to be more susceptible to peptide action compared with DMPS bilayer. In the latter case, long-time exposure to melittin does not result in the rupture of the membrane but rather leads to formation of pore-like defects. This observation is explained in terms of different nanomechanical properties of DMPG and DMPS films and different barrier for the reorientation and insertion of the peptide molecules into the membranes.

Effective Brownian ratchet separation by a combination of molecular filtering and a self-spreading lipid bilayer system.

Science.gov (United States)

Motegi, Toshinori; Nabika, Hideki; Fu, Yingqiang; Chen, Lili; Sun, Yinlu; Zhao, Jianwei; Murakoshi, Kei

2014-07-01

A new molecular manipulation method in the self-spreading lipid bilayer membrane by combining Brownian ratchet and molecular filtering effects is reported. The newly designed ratchet obstacle was developed to effectively separate dye-lipid molecules. The self-spreading lipid bilayer acted as both a molecular transport system and a manipulation medium. By controlling the size and shape of ratchet obstacles, we achieved a significant increase in the separation angle for dye-lipid molecules compared to that with the previous ratchet obstacle. A clear difference was observed between the experimental results and the simple random walk simulation that takes into consideration only the geometrical effect of the ratchet obstacles. This difference was explained by considering an obstacle-dependent local decrease in molecular diffusivity near the obstacles, known as the molecular filtering effect at nanospace. Our experimental findings open up a novel controlling factor in the Brownian ratchet manipulation that allow the efficient separation of molecules in the lipid bilayer based on the combination of Brownian ratchet and molecular filtering effects.

Cholesterol enhances surface water diffusion of phospholipid bilayers

Energy Technology Data Exchange (ETDEWEB)

Cheng, Chi-Yuan; Kausik, Ravinath; Han, Songi, E-mail: songi@chem.ucsb.edu [Department of Chemistry and Biochemistry and Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States); Olijve, Luuk L. C. [Laboratory of Macromolecular and Organic Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven (Netherlands)

2014-12-14

Elucidating the physical effect of cholesterol (Chol) on biological membranes is necessary towards rationalizing their structural and functional role in cell membranes. One of the debated questions is the role of hydration water in Chol-embedding lipid membranes, for which only little direct experimental data are available. Here, we study the hydration dynamics in a series of Chol-rich and depleted bilayer systems using an approach termed {sup 1}H Overhauser dynamic nuclear polarization (ODNP) NMR relaxometry that enables the sensitive and selective determination of water diffusion within 5–10 Å of a nitroxide-based spin label, positioned off the surface of the polar headgroups or within the nonpolar core of lipid membranes. The Chol-rich membrane systems were prepared from mixtures of Chol, dipalmitoyl phosphatidylcholine and/or dioctadecyl phosphatidylcholine lipid that are known to form liquid-ordered, raft-like, domains. Our data reveal that the translational diffusion of local water on the surface and within the hydrocarbon volume of the bilayer is significantly altered, but in opposite directions: accelerated on the membrane surface and dramatically slowed in the bilayer interior with increasing Chol content. Electron paramagnetic resonance (EPR) lineshape analysis shows looser packing of lipid headgroups and concurrently tighter packing in the bilayer core with increasing Chol content, with the effects peaking at lipid compositions reported to form lipid rafts. The complementary capability of ODNP and EPR to site-specifically probe the hydration dynamics and lipid ordering in lipid membrane systems extends the current understanding of how Chol may regulate biological processes. One possible role of Chol is the facilitation of interactions between biological constituents and the lipid membrane through the weakening or disruption of strong hydrogen-bond networks of the surface hydration layers that otherwise exert stronger repulsive forces, as reflected in

Study of the ion-channel behavior on glassy carbon electrode supported bilayer lipid membranes stimulated by perchlorate anion

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zhiquan; Shi, Jun; Huang, Weimin, E-mail: huangwm@jlu.edu.cn

2015-10-01

In this paper, a kind of didodecyldimethylammonium bromide (DDAB) layer membranes was supported on a glassy carbon electrode (GCE). We studied the ion channel behavior of the supported bilayer lipid membrane by scanning electrochemical microscopy (SCEM) in tris(2,2′-bipyridine) ruthenium(II) solution. Perchlorate anion was used as a presence of stimulus and ruthenium(II) complex cations as the probing ions for the measurement of SECM, the lipid membrane channel was opened and exhibited the behavior of distinct SECM positive feedback curve. The channel was in a closed state in the absence of perchlorate anions while reflected the behavior of SECM negative feedback curve. The rates of electron transfer reaction in the lipid membranes surface were detected and it was dependant on the potential of SECM. - Highlights: • The rates of electron transfer reaction in the lipid membranes surface were detected. • Dynamic investigations of ion-channel behavior of supported bilayer lipid membranes by scanning electrochemical microscopy • A novel way to explore the interaction between molecules and supported bilayer lipid membranes.

The role of polyglutamine expansion and protein context in disease-related huntingtin/lipid interactions

Science.gov (United States)

Burke, Kathleen Anne

Huntington's Disease (HD) is a neurodegenerative disorder that is defined by the accumulation of nanoscale aggregates comprised of the huntingtin (htt) protein. Aggregation is directly caused by an expanded polyglutamine (polyQ) domain in htt, leading to a diverse population of aggregate species, such as oligomers, fibrils, and annular aggregates. Furthermore, the length of this polyQ domain is directly related to onset and severity of disease. The first 17 amino acids on the N-terminus (N17) and the polyproline domain on the C-terminal side of the polyQ domain have been shown to further modulate the aggregation process. Additionally, N17 appears to have lipid binding properties as htt interacts with a variety of membrane-containing structures present in cells, such as organelles, and interactions with these membrane surfaces may further modulate htt aggregation. To investigate the interaction between htt exon1 and lipid bilayers, in situ atomic force microscopy (AFM) was used to directly monitor the aggregation of htt exon1 constructs with varying Q-length (35Q, 46Q, 51Q, and myc- 53Q) or synthetic peptides with different polyQ domain flanking sequences (KK-Q35-KK, KK-Q 35-P10-KK, N17-Q35-KK, and N 17-Q35-P10-KK) on supported lipid membranes comprised of total brain lipid extract. The exon1 fragments accumulated on the lipid membranes, causing disruption of the membrane, in a polyQ dependent manner. By adding N-terminal tags to the htt exon1 fragments, the interaction with the lipid bilayer was impeded. The KK-Q35-KK and KK-Q 35-P10-KK peptides had no appreciable interaction with lipid bilayers. Interestingly, polyQ peptides with the N17 flanking sequence interacted with the bilayer. N17-Q35-KK formed discrete aggregates on the bilayer, but there was minimal membrane disruption. The N17-Q35-P10-KK peptide interacted more aggressively with the lipid bilayer in a manner reminiscent of the htt exon1 proteins.

Multidimensional oriented solid-state NMR experiments enable the sequential assignment of uniformly 15N labeled integral membrane proteins in magnetically aligned lipid bilayers

International Nuclear Information System (INIS)

Mote, Kaustubh R.; Gopinath, T.; Traaseth, Nathaniel J.; Kitchen, Jason; Gor’kov, Peter L.; Brey, William W.; Veglia, Gianluigi

2011-01-01

Oriented solid-state NMR is the most direct methodology to obtain the orientation of membrane proteins with respect to the lipid bilayer. The method consists of measuring 1 H- 15 N dipolar couplings (DC) and 15 N anisotropic chemical shifts (CSA) for membrane proteins that are uniformly aligned with respect to the membrane bilayer. A significant advantage of this approach is that tilt and azimuthal (rotational) angles of the protein domains can be directly derived from analytical expression of DC and CSA values, or, alternatively, obtained by refining protein structures using these values as harmonic restraints in simulated annealing calculations. The Achilles’ heel of this approach is the lack of suitable experiments for sequential assignment of the amide resonances. In this Article, we present a new pulse sequence that integrates proton driven spin diffusion (PDSD) with sensitivity-enhanced PISEMA in a 3D experiment ([ 1 H, 15 N]-SE-PISEMA-PDSD). The incorporation of 2D 15 N/ 15 N spin diffusion experiments into this new 3D experiment leads to the complete and unambiguous assignment of the 15 N resonances. The feasibility of this approach is demonstrated for the membrane protein sarcolipin reconstituted in magnetically aligned lipid bicelles. Taken with low electric field probe technology, this approach will propel the determination of sequential assignment as well as structure and topology of larger integral membrane proteins in aligned lipid bilayers.

Conformational study of the protegrin-1 (PG-1 dimer interaction with lipid bilayers and its effect

Directory of Open Access Journals (Sweden)

Nussinov Ruth

2007-04-01

Full Text Available Abstract Background Protegrin-1 (PG-1 is known as a potent antibiotic peptide; it prevents infection via an attack on the membrane surface of invading microorganisms. In the membrane, the peptide forms a pore/channel through oligomerization of multiple subunits. Recent experimental and computational studies have increasingly unraveled the molecular-level mechanisms underlying the interactions of the PG-1 β-sheet motifs with the membrane. The PG-1 dimer is important for the formation of oligomers, ordered aggregates, and for membrane damaging effects. Yet, experimentally, different dimeric behavior has been observed depending on the environment: antiparallel in the micelle environment, and parallel in the POPC bilayer. The experimental structure of the PG-1 dimer is currently unavailable. Results Although the β-sheet structures of the PG-1 dimer are less stable in the bulk water environment, the dimer interface is retained by two intermolecular hydrogen bonds. The formation of the dimer in the water environment implies that the pathway of the dimer invasion into the membrane can originate from the bulk region. In the initial contact with the membrane, both the antiparallel and parallel β-sheet conformations of the PG-1 dimer are well preserved at the amphipathic interface of the lipid bilayer. These β-sheet structures illustrate the conformations of PG-1 dimer in the early stage of the membrane attack. Here we observed that the activity of PG-1 β-sheets on the bilayer surface is strongly correlated with the dimer conformation. Our long-term goal is to provide a detailed mechanism of the membrane-disrupting effects by PG-1 β-sheets which are able to attack the membrane and eventually assemble into the ordered aggregates. Conclusion In order to understand the dimeric effects leading to membrane damage, extensive molecular dynamics (MD simulations were performed for the β-sheets of the PG-1 dimer in explicit water, salt, and lipid bilayers

Strong influence of periodic boundary conditions on lateral diffusion in lipid bilayer membranes

Energy Technology Data Exchange (ETDEWEB)

Camley, Brian A. [Center for Theoretical Biological Physics and Department of Physics, University of California, San Diego, California 92093 (United States); Department of Physics, University of California, Santa Barbara, California 93106 (United States); Lerner, Michael G. [Department of Physics and Astronomy, Earlham College, Richmond, Indiana 47374 (United States); Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892 (United States); Pastor, Richard W. [Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892 (United States); Brown, Frank L. H. [Department of Physics, University of California, Santa Barbara, California 93106 (United States); Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States)

2015-12-28

The Saffman-Delbrück hydrodynamic model for lipid-bilayer membranes is modified to account for the periodic boundary conditions commonly imposed in molecular simulations. Predicted lateral diffusion coefficients for membrane-embedded solid bodies are sensitive to box shape and converge slowly to the limit of infinite box size, raising serious doubts for the prospects of using detailed simulations to accurately predict membrane-protein diffusivities and related transport properties. Estimates for the relative error associated with periodic boundary artifacts are 50% and higher for fully atomistic models in currently feasible simulation boxes. MARTINI simulations of LacY membrane protein diffusion and LacY dimer diffusion in DPPC membranes and lipid diffusion in pure DPPC bilayers support the underlying hydrodynamic model.

Strong influence of periodic boundary conditions on lateral diffusion in lipid bilayer membranes

International Nuclear Information System (INIS)

Camley, Brian A.; Lerner, Michael G.; Pastor, Richard W.; Brown, Frank L. H.

2015-01-01

The Saffman-Delbrück hydrodynamic model for lipid-bilayer membranes is modified to account for the periodic boundary conditions commonly imposed in molecular simulations. Predicted lateral diffusion coefficients for membrane-embedded solid bodies are sensitive to box shape and converge slowly to the limit of infinite box size, raising serious doubts for the prospects of using detailed simulations to accurately predict membrane-protein diffusivities and related transport properties. Estimates for the relative error associated with periodic boundary artifacts are 50% and higher for fully atomistic models in currently feasible simulation boxes. MARTINI simulations of LacY membrane protein diffusion and LacY dimer diffusion in DPPC membranes and lipid diffusion in pure DPPC bilayers support the underlying hydrodynamic model

Acceleration of Lateral Equilibration in Mixed Lipid Bilayers Using Replica Exchange with Solute Tempering.

Science.gov (United States)

Huang, Kun; García, Angel E

2014-10-14

The lateral heterogeneity of cellular membranes plays an important role in many biological functions such as signaling and regulating membrane proteins. This heterogeneity can result from preferential interactions between membrane components or interactions with membrane proteins. One major difficulty in molecular dynamics simulations aimed at studying the membrane heterogeneity is that lipids diffuse slowly and collectively in bilayers, and therefore, it is difficult to reach equilibrium in lateral organization in bilayer mixtures. Here, we propose the use of the replica exchange with solute tempering (REST) approach to accelerate lateral relaxation in heterogeneous bilayers. REST is based on the replica exchange method but tempers only the solute, leaving the temperature of the solvent fixed. Since the number of replicas in REST scales approximately only with the degrees of freedom in the solute, REST enables us to enhance the configuration sampling of lipid bilayers with fewer replicas, in comparison with the temperature replica exchange molecular dynamics simulation (T-REMD) where the number of replicas scales with the degrees of freedom of the entire system. We apply the REST method to a cholesterol and 1,2-dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) bilayer mixture and find that the lateral distribution functions of all molecular pair types converge much faster than in the standard MD simulation. The relative diffusion rate between molecules in REST is, on average, an order of magnitude faster than in the standard MD simulation. Although REST was initially proposed to study protein folding and its efficiency in protein folding is still under debate, we find a unique application of REST to accelerate lateral equilibration in mixed lipid membranes and suggest a promising way to probe membrane lateral heterogeneity through molecular dynamics simulation.

Molecular dynamics simulations of the interactions of medicinal plant extracts and drugs with lipid bilayer membranes

DEFF Research Database (Denmark)

Kopec, Wojciech; Telenius, Jelena; Khandelia, Himanshu

2013-01-01

Several small drugs and medicinal plant extracts, such as the Indian spice extract curcumin, have a wide range of useful pharmacological properties that cannot be ascribed to binding to a single protein target alone. The lipid bilayer membrane is thought to mediate the effects of many such molecu......Several small drugs and medicinal plant extracts, such as the Indian spice extract curcumin, have a wide range of useful pharmacological properties that cannot be ascribed to binding to a single protein target alone. The lipid bilayer membrane is thought to mediate the effects of many...

Effect of intra-membrane C60 fullerenes on the modulus of elasticity and the mechanical resistance of gel and fluid lipid bilayers

Science.gov (United States)

Zhou, Jihan; Liang, Dehai; Contera, Sonia

2015-10-01

Penetration and partition of C60 to the lipid bilayer core are both relevant to C60 toxicity, and useful to realise C60 biomedical potential. A key aspect is the effect of C60 on bilayer mechanical properties. Here, we present an experimental study on the mechanical effect of the incorporation of C60 into the hydrophobic core of fluid and gel phase zwitterionic phosphatidylcholine (PC) lipid bilayers. We demonstrate its incorporation inside the hydrophobic lipid core and the effect on the packing of the lipids and the vesicle size using a combination of infrared (IR) spectroscopy, atomic force microscopy (AFM) and laser light scattering. Using AFM we measured the Young's modulus of elasticity (E) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) in the absence (presence) of intra-membranous C60 at 24.5 °C. E of fluid phase supported bilayers is not altered by C60, but E increases with incorporation of C60 in gel phase bilayers. The increase is higher for longer hydrocarbon chains: 1.6 times for DPPC and 2 times for DSPC. However the mechanical resistance of gel phase bilayers of curved bilayered structures decreases with the incorporation of C60. Our combined results indicate that C60 causes a decrease in gel phase lipid mobility, i.e. an increase in membrane viscosity.

Calculation of the electrostatic potential of lipid bilayers from molecular dynamics simulations: methodological issues

DEFF Research Database (Denmark)

Gurtovenko, Andrey A; Vattulainen, Ilpo

2009-01-01

of the electrostatic potential from atomic-scale molecular dynamics simulations of lipid bilayers. We discuss two slightly different forms of Poisson equation that are normally used to calculate the membrane potential: (i) a classical form when the potential and the electric field are chosen to be zero on one...... systems). For symmetric bilayers we demonstrate that both approaches give essentially the same potential profiles, provided that simulations are long enough (a production run of at least 100 ns is required) and that fluctuations of the center of mass of a bilayer are properly accounted for. In contrast...

The effects of ethylene oxide containing lipopolymers and tri-block copolymers on lipid bilayers of dipalmitoylphosphatidylcholine

DEFF Research Database (Denmark)

Baekmark, T. R.; Pedersen, S.; Jorgensen, K.

1997-01-01

oxide moity, anchored to the bilayer by a 1,2-dioctadecanoyl-s,n-glycero-3-phosphoethanolamine (DC18PE) lipid. The second type, which is a novel type of membrane-spanning object, is an amphiphilic tri-block copolymer composed of two hydrophilic stretches of polyethylene oxide separated by a hydrophobic...... stretch of polystyrene. Hence the tri-block copolymer may act as a membrane-spanning macromolecule mimicking an amphiphilic protein or polypeptide. Differential scanning calorimetry is used to determine a partial phase diagram for the lipopolymer systems and to assess the amount of lipopolymer that can...... be loaded into DC16PC lipid bilayers before micellization takes place. Unilamellar and micellar phase structures are investigated by fluorescence quenching using bilayer permeating dithionite. The chain length-dependent critical lipopolymer concentration, denoting the lamellar-to-micellar phase transition...

Single-molecule study of full-length NaChBac by planar lipid bilayer recording.

Directory of Open Access Journals (Sweden)

Andrew Jo

Full Text Available Planar lipid bilayer device, alternatively known as BLM, is a powerful tool to study functional properties of conducting membrane proteins such as ion channels and porins. In this work, we used BLM to study the prokaryotic voltage-gated sodium channel (Nav NaChBac in a well-defined membrane environment. Navs are an essential component for the generation and propagation of electric signals in excitable cells. The successes in the biochemical, biophysical and crystallographic studies on prokaryotic Navs in recent years has greatly promoted the understanding of the molecular mechanism that underlies these proteins and their eukaryotic counterparts. In this work, we investigated the single-molecule conductance and ionic selectivity behavior of NaChBac. Purified NaChBac protein was first reconstituted into lipid vesicles, which is subsequently incorporated into planar lipid bilayer by fusion. At single-molecule level, we were able to observe three distinct long-lived conductance sub-states of NaChBac. Change in the membrane potential switches on the channel mainly by increasing its opening probability. In addition, we found that individual NaChBac has similar permeability for Na+, K+, and Ca2+. The single-molecule behavior of the full-length protein is essentially highly stochastic. Our results show that planar lipid bilayer device can be used to study purified ion channels at single-molecule level in an artificial environment, and such studies can reveal new protein properties that are otherwise not observable in in vivo ensemble studies.

/SIGMA PHI/-tocopherol: modifier of the phase state of the lipid bilayer

International Nuclear Information System (INIS)

Skrypin, V.I.; Bratkcovskaya, L.B.; Erin, A.N.; Kagan, V.E.

1985-01-01

This paper determines the action of low (near-physiological) concentrations of alpha-tocopherol on the character of the gel-liquid crystal transition in a lipid bilayer containing free fatty acids. Fifty mM of K + -phosphate buffer was made up in D 2 O and kept for several hours to enable substitution of H 1 by D 2, after which the buffer was dried and redissolved in D 2 O. The graphs of temperature dependence of relative signal intensity of protons of methylene groups in liposomes of different composition are presented. It is shown that the stabilizing action of alpha-tocopherol on the phase state of the lipid bilayer of membranes is one of the mechanisms by which the recently demonstrated ability of alpha-tocopherol to protect biological membranes against the injurious action of free fatty acids, through the formation of complexes of alpha-tocopherol with fatty acides, may be effected

The structure of the CD3 ζζ transmembrane dimer in POPC and raft-like lipid bilayer: a molecular dynamics study.

Science.gov (United States)

Petruk, Ariel Alcides; Varriale, Sonia; Coscia, Maria Rosaria; Mazzarella, Lelio; Merlino, Antonello; Oreste, Umberto

2013-11-01

Plasma membrane lipids significantly affect assembly and activity of many signaling networks. The present work is aimed at analyzing, by molecular dynamics simulations, the structure and dynamics of the CD3 ζζ dimer in palmitoyl-oleoyl-phosphatidylcholine bilayer (POPC) and in POPC/cholesterol/sphingomyelin bilayer, which resembles the raft membrane microdomain supposed to be the site of the signal transducing machinery. Both POPC and raft-like environment produce significant alterations in structure and flexibility of the CD3 ζζ with respect to nuclear magnetic resonance (NMR) model: the dimer is more compact, its secondary structure is slightly less ordered, the arrangement of the Asp6 pair, which is important for binding to the Arg residue in the alpha chain of the T cell receptor (TCR), is stabilized by water molecules. Different interactions of charged residues with lipids at the lipid-cytoplasm boundary occur when the two environments are compared. Furthermore, in contrast to what is observed in POPC, in the raft-like environment correlated motions between transmembrane and cytoplasmic regions are observed. Altogether the data suggest that when the TCR complex resides in the raft domains, the CD3 ζζ dimer assumes a specific conformation probably necessary to the correct signal transduction. © 2013.

On-Chip Electrophoresis in Supported Lipid Bilayer Membranes Achieved Using Low Potentials

NARCIS (Netherlands)

van Weerd, Jasper; Krabbenborg, Sven; Eijkel, Jan C.T.; Karperien, Hermanus Bernardus Johannes; Huskens, Jurriaan; Jonkheijm, Pascal

2014-01-01

A micro supported lipid bilayer (SLB) electrophoresis method was developed, which functions at low potentials and appreciable operating times. To this end, (hydroxymethyl)-ferrocene (FcCH2OH) was employed to provide an electrochemical reaction at the anode and cathode at low applied potential to

Hydrogel Micro-/Nanosphere Coated by a Lipid Bilayer: Preparation and Microscopic Probing

Directory of Open Access Journals (Sweden)

Sarah Rahni

2017-02-01

Full Text Available The result of polymeric nanogels and lipid vesicles interaction—lipobeads—can be considered as multipurpose containers for future therapeutic applications, such as targeted anticancer chemotherapy with superior tumor response and minimum side effects. In this work, micrometer sized lipobeads were synthesized by two methods: (i mixing separately prepared microgels made of poly(N-isopropylacrylamide (PNIPA and phospholipid vesicles of micrometer or nanometer size and (ii polymerization within the lipid vesicles. For the first time, a high vacuum scanning electron microscopy was shown to be suitable for a quick validation of the structural organization of wet lipobeads and their constituents without special sample preparation. In particular, the structural difference of microgels prepared by thermal and UV-polymerization in different solvents was revealed and three types of giant liposomes were recognized under high vacuum in conjunction with their size, composition, and method of preparation. Importantly, the substructure of the hydrogel core and multi- and unilamellar constructions of the peripheral lipid part were explicitly distinguished on the SEM images of lipobeads, justifying the spontaneous formation of a lipid bilayer on the surface of microgels and evidencing an energetically favorable structural organization of the hydrogel/lipid bilayer assembly. This key property can facilitate lipobeads’ preparation and decrease technological expenses on their scaled production. The comparison of the SEM imaging with the scanning confocal and atomic force microscopies data are also presented in the discussion.

Multidimensional oriented solid-state NMR experiments enable the sequential assignment of uniformly 15N labeled integral membrane proteins in magnetically aligned lipid bilayers.

Science.gov (United States)

Mote, Kaustubh R; Gopinath, T; Traaseth, Nathaniel J; Kitchen, Jason; Gor'kov, Peter L; Brey, William W; Veglia, Gianluigi

2011-11-01

Oriented solid-state NMR is the most direct methodology to obtain the orientation of membrane proteins with respect to the lipid bilayer. The method consists of measuring (1)H-(15)N dipolar couplings (DC) and (15)N anisotropic chemical shifts (CSA) for membrane proteins that are uniformly aligned with respect to the membrane bilayer. A significant advantage of this approach is that tilt and azimuthal (rotational) angles of the protein domains can be directly derived from analytical expression of DC and CSA values, or, alternatively, obtained by refining protein structures using these values as harmonic restraints in simulated annealing calculations. The Achilles' heel of this approach is the lack of suitable experiments for sequential assignment of the amide resonances. In this Article, we present a new pulse sequence that integrates proton driven spin diffusion (PDSD) with sensitivity-enhanced PISEMA in a 3D experiment ([(1)H,(15)N]-SE-PISEMA-PDSD). The incorporation of 2D (15)N/(15)N spin diffusion experiments into this new 3D experiment leads to the complete and unambiguous assignment of the (15)N resonances. The feasibility of this approach is demonstrated for the membrane protein sarcolipin reconstituted in magnetically aligned lipid bicelles. Taken with low electric field probe technology, this approach will propel the determination of sequential assignment as well as structure and topology of larger integral membrane proteins in aligned lipid bilayers. © Springer Science+Business Media B.V. 2011

Localization and Orientation of Xanthophylls in a Lipid Bilayer.

Science.gov (United States)

Grudzinski, Wojciech; Nierzwicki, Lukasz; Welc, Renata; Reszczynska, Emilia; Luchowski, Rafal; Czub, Jacek; Gruszecki, Wieslaw I

2017-08-29

Xanthophylls (polar carotenoids) play diverse biological roles, among which are modulation of the physical properties of lipid membranes and protection of biomembranes against oxidative damage. Molecular mechanisms underlying these functions are intimately related to the localization and orientation of xanthophyll molecules in lipid membranes. In the present work, we address the problem of localization and orientation of two xanthophylls present in the photosynthetic apparatus of plants and in the retina of the human eye, zeaxanthin and lutein, in a single lipid bilayer membrane formed with dimyristoylphosphatidylcholine. By using fluorescence microscopic analysis and Raman imaging of giant unilamellar vesicles, as well as molecular dynamics simulations, we show that lutein and zeaxanthin adopt a very similar transmembrane orientation within a lipid membrane. In experimental and computational approach, the average tilt angle of xanthophylls relative to the membrane normal is independently found to be ~40 deg, and results from hydrophobic mismatch between the membrane thickness and the distance between the terminal hydroxyl groups of the xanthophylls. Consequences of such a localization and orientation for biological activity of xanthophylls are discussed.

On the freezing behavior and diffusion of water in proximity to single-supported zwitterionic and anionic bilayer lipid membranes

DEFF Research Database (Denmark)

Miskowiec, A.; Buck, Z. N.; Brown, M. C.

2014-01-01

We compare the freezing/melting behavior of water hydrating single-supported bilayers of a zwitterionic lipid DMPC with that of an anionic lipid DMPG. For both membranes, the temperature dependence of the elastically scattered neutron intensity indicates distinct water types undergoing...... translational diffusion: bulk-like water probably located above the membrane and two types of confined water closer to the lipid head groups. The membranes differ in the greater width of the water freezing transition near the anionic DMPG bilayer compared to zwitterionic DMPC as well as in the abruptness...

Ripples and the formation of anisotropic lipid domains: Imaging two-component double bilayers by atomic force microscopy_copy_03

DEFF Research Database (Denmark)

Leidy, C.; Kaasgaard, Thomas; Crowe, J.H.

2002-01-01

by atomic force microscopy, we investigated the origin of these anisotropic lipid domain patterns, and found that ripple phase formation is directly responsible for the anisotropic nature of these domains. The nucleation and growth of fluid-phase domains are found to be directed by the presence of ripples....... In particular, the fluid-phase domains elongate parallel to the ripples. The results show that ripple phase formation may have implications for domain formation in biological systems....

Micromagnetic analysis of current-induced domain wall motion in a bilayer nanowire with synthetic antiferromagnetic coupling

Energy Technology Data Exchange (ETDEWEB)

Komine, Takashi, E-mail: komine@mx.ibaraki.ac.jp; Aono, Tomosuke [Faculty of Engineering, Ibaraki University 4-12-1, Nakanarusawa, Hitachi, Ibaraki, 316-8511 (Japan)

2016-05-15

We demonstrate current-induced domain wall motion in bilayer nanowire with synthetic antiferromagnetic (SAF) coupling by modeling two body problems for motion equations of domain wall. The influence of interlayer exchange coupling and magnetostatic interactions on current-induced domain wall motion in SAF nanowires was also investigated. By assuming the rigid wall model for translational motion, the interlayer exchange coupling and the magnetostatic interaction between walls and domains in SAF nanowires enhances domain wall speed without any spin-orbit-torque. The enhancement of domain wall speed was discussed by energy distribution as a function of wall angle configuration in bilayer nanowires.

Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ.

Science.gov (United States)

Pohl, P; Saparov, S M; Borgnia, M J; Agre, P

2001-08-14

Aquaporins are membrane channels selectively permeated by water or water plus glycerol. Conflicting reports have described ion conductance associated with some water channels, raising the question of whether ion conductance is a general property of the aquaporin family. To clarify this question, a defined system was developed to simultaneously measure water permeability and ion conductance. The Escherichia coli water channel aquaporin-Z (AqpZ) was studied, because it is a highly stable tetramer. Planar lipid bilayers were formed from unilamellar vesicles containing purified AqpZ. The hydraulic conductivity of bilayers made from the total extract of E. coli lipids increased 3-fold if reconstituted with AqpZ, but electric conductance was unchanged. No channel activity was detected under voltage-clamp conditions, indicating that less than one in 10(9) transport events is electrogenic. Microelectrode measurements were simultaneously undertaken adjacent to the membrane. Changes in sodium concentration profiles accompanying transmembrane water flow permitted calculation of the activation energies: 14 kcal/mol for protein-free lipid bilayers and 4 kcal/mol for lipid bilayers containing AqpZ. Neither the water permeability nor the electric conductivity exhibited voltage dependence. This sensitive system demonstrated that AqpZ is permeated by water but not charged ions and should permit direct analyses of putative electrogenic properties of other aquaporins.

Accelerating Convergence in Molecular Dynamics Simulations of Solutes in Lipid Membranes by Conducting a Random Walk along the Bilayer Normal.

Science.gov (United States)

Neale, Chris; Madill, Chris; Rauscher, Sarah; Pomès, Régis

2013-08-13

All molecular dynamics simulations are susceptible to sampling errors, which degrade the accuracy and precision of observed values. The statistical convergence of simulations containing atomistic lipid bilayers is limited by the slow relaxation of the lipid phase, which can exceed hundreds of nanoseconds. These long conformational autocorrelation times are exacerbated in the presence of charged solutes, which can induce significant distortions of the bilayer structure. Such long relaxation times represent hidden barriers that induce systematic sampling errors in simulations of solute insertion. To identify optimal methods for enhancing sampling efficiency, we quantitatively evaluate convergence rates using generalized ensemble sampling algorithms in calculations of the potential of mean force for the insertion of the ionic side chain analog of arginine in a lipid bilayer. Umbrella sampling (US) is used to restrain solute insertion depth along the bilayer normal, the order parameter commonly used in simulations of molecular solutes in lipid bilayers. When US simulations are modified to conduct random walks along the bilayer normal using a Hamiltonian exchange algorithm, systematic sampling errors are eliminated more rapidly and the rate of statistical convergence of the standard free energy of binding of the solute to the lipid bilayer is increased 3-fold. We compute the ratio of the replica flux transmitted across a defined region of the order parameter to the replica flux that entered that region in Hamiltonian exchange simulations. We show that this quantity, the transmission factor, identifies sampling barriers in degrees of freedom orthogonal to the order parameter. The transmission factor is used to estimate the depth-dependent conformational autocorrelation times of the simulation system, some of which exceed the simulation time, and thereby identify solute insertion depths that are prone to systematic sampling errors and estimate the lower bound of the

The H2O/D2O exchange across vesicular lipid bilayers

International Nuclear Information System (INIS)

Engelbert, H.P.; Lawaczek, R.

1985-01-01

A new method to measure the water (D 2 O/H 2 O) permeation across vesicular lipid bilayers is described. The method is based on the solvent isotope effect of the light scattering which is a consequence of the different indices of refraction of D 2 O and H 2 O. Unilamellar lipid vesicles in excess of H 2 O are rapidly mixed with D 2 O or vice versa. As result of the H 2 O/D 2 O exchange across the vesicular bilayer the light scattering signal has a time dependent, almost single exponential component allowing the deduction of the exchange relaxation rate and, at known size, of the permeability coefficient. The experimental results are in accord with calculations from the Mie theory of light scattering for coated spheres. The method is applicable for large vesicles where the permeation is the rate-limiting step. Size separations are performed by a flow dialysis through a sequence of pore-membrane-filters. For dimyristoyl-lecithin bilayers the water permeability-coefficient is 1.9 . 10 -5 cm/s in the crystalline phase and increases by a factor of 10-100 in the liquid-crystalline state. The temperature dependence of the permeation exhibits a sharp change at the phase transition. For binary mixtures of lecithins this sharp change follows the solidus curve of the non-ideal phase diagram determined by spectroscopic techniques. (orig.)

Investigation of lipid membrane macro- and micro-structure using calorimetry and computer simulation: structural and functional relationships

DEFF Research Database (Denmark)

Jørgensen, Kent; Mouritsen, Ole G.

1999-01-01

lead to the formation of a heterogeneous lateral bilayer structure composed of dynamic lipid domains and differentiated bilayer regions. In addition, the non-equilibrium dynamic ordering process of coexisting phases can give rise to the formation of local lipid structures on various length- and time...

Lipid bilayers driven to a wrong lane in molecular dynamics simulations by subtle changes in long-range electrostatic interactions

NARCIS (Netherlands)

Patra, M.; Karttunen, M.E.J.; Hyvönen, M.T.; Falck, E.; Vattulainen, I.

2004-01-01

We provide compelling evidence that different treatments of electrostatic interactions in molecular dynamics simulations may dramatically affect dynamic properties of lipid bilayers. To this end, we consider a fully hydrated pure dipalmitoylphosphatidylcholine bilayer through 50-ns molecular

Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

International Nuclear Information System (INIS)

Rønnest, A. K.; Peters, G. H.; Hansen, F. Y.; Taub, H.; Miskowiec, A.

2016-01-01

Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic potential within phospholipid membranes imply an enormous electric field of 10 8 –10 9 V m −1 , which is likely to have great significance in controlling the conformation of translocating membrane proteins and in the transfer of ions and molecules across the membrane. We have calculated the membrane potential for DMPG bilayers and found ∼1 V (∼2 ⋅ 10 8 V m −1 ) when in the fluid phase with a monovalent counter-ion and ∼1.4 V (∼2.8 ⋅ 10 8 V m −1 ) when in the gel phase with a divalent counter-ion. The number of water molecules for a fully hydrated DMPG membrane has been estimated to be 9.7 molecules per lipid in the gel phase and 17.5 molecules in the fluid phase, considerably smaller than inferred experimentally for 1,2-dimyristoyl-sn-glycero-3

Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

Energy Technology Data Exchange (ETDEWEB)

Rønnest, A. K.; Peters, G. H.; Hansen, F. Y., E-mail: flemming@kemi.dtu.dk [Department of Chemistry, Technical University of Denmark, IK 207 DTU, DK-2800 Lyngby (Denmark); Taub, H.; Miskowiec, A. [Department of Physics and Astronomy and the University of Missouri Research Reactor,University of Missouri, Columbia, Missouri 65211 (United States)

2016-04-14

Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic potential within phospholipid membranes imply an enormous electric field of 10{sup 8}–10{sup 9} V m{sup −1}, which is likely to have great significance in controlling the conformation of translocating membrane proteins and in the transfer of ions and molecules across the membrane. We have calculated the membrane potential for DMPG bilayers and found ∼1 V (∼2 ⋅ 10{sup 8} V m{sup −1}) when in the fluid phase with a monovalent counter-ion and ∼1.4 V (∼2.8 ⋅ 10{sup 8} V m{sup −1}) when in the gel phase with a divalent counter-ion. The number of water molecules for a fully hydrated DMPG membrane has been estimated to be 9.7 molecules per lipid in the gel phase and 17.5 molecules in the fluid phase, considerably smaller than inferred experimentally for 1

Equilibrium and non-equilibrium conformations of peptides in lipid bilayers.

Science.gov (United States)

Boden, N; Cheng, Y; Knowles, P F

1997-04-22

A synthetic, hydrophobic, 27-amino-acid-residue peptide 'K27', modelled on the trans-membrane domain of the slow voltage-gated potassium channel, IsK, has been incorporated into a lipid bilayer and its conformational properties studied using FT-IR spectroscopy. The conformation following reconstitution is found to be dependent on the nature of the solvent employed. When the reconstitution is conducted by solvent evaporation from a methanol solution, aggregates comprised of beta-strands are stabilised and their concentration is essentially invariant with time. By contrast, when trifluoroethanol is used, the initial conformation of the peptide is alpha-helical. This then relaxes to an equilibrium state between alpha-helices and beta-strands. The alpha-helix-to beta-strand conversion rate is relatively slow, and this allows the kinetics to be studied by FT-IR spectroscopy. The reverse process is much slower but again can be demonstrated by FT-IR. Thus, it appears that a true equilibrium structure can only be achieved by starting with peptide in the alpha-helical conformation. We believe this result should be of general validity for hydrophobic peptide reconstitution. The implications for conformational changes in membrane proteins are discussed.

Study of water diffusion on single-supported bilayer lipid membranes by quasielastic neutron scattering

DEFF Research Database (Denmark)

Bai, M.; Miskowiec, A.; Hansen, F. Y.

2012-01-01

High-energy-resolution quasielastic neutron scattering has been used to elucidate the diffusion of water molecules in proximity to single bilayer lipid membranes supported on a silicon substrate. By varying sample temperature, level of hydration, and deuteration, we identify three different types...... of diffusive water motion: bulk-like, confined, and bound. The motion of bulk-like and confined water molecules is fast compared to those bound to the lipid head groups (7-10 H2O molecules per lipid), which move on the same nanosecond time scale as H atoms within the lipid molecules. Copyright (C) EPLA, 2012...

Lipid peroxidation and water penetration in lipid bilayers

DEFF Research Database (Denmark)

Conte, Elena; Megli, Francesco Maria; Khandelia, Himanshu

2012-01-01

to the hydroperoxide groups to interact with the nitroxide at the methyl-terminal, confirming that the H-bonds experimentally observed are due to increased water penetration in the bilayer. The EPR and MD data on model membranes demonstrate that cell membrane damage by oxidative stress cause alteration of water......(zz) parameters revealed that OHPLPC, but mostly HpPLPC, induced a measurable increase in polarity and H-bonding propensity in the central region of the bilayer. Molecular dynamics simulation performed on 16-DSA in the PLPC-HpPLPC bilayer revealed that water molecules are statistically favored with respect...

Atomic force microscopy on domains in biological model membranes

NARCIS (Netherlands)

Rinia, H.A.

2001-01-01

This thesis describes the preparation and imaging of supported lipid bilayers, which can be regarded as biological modelmembranes, in the light of the formation of domains. The bilayers were prepared with either the Langmuir-Blodgett method, or with vesicle fusion. They were imaged with Atomic Force

Mixed bilayer containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine: lipid complexation, ion binding, and electrostatics.

Science.gov (United States)

Pandit, Sagar A; Bostick, David; Berkowitz, Max L

2003-11-01

Two mixed bilayers containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine at a ratio of 5:1 are simulated in NaCl electrolyte solutions of different concentration using the molecular dynamics technique. Direct NH.O and CH.O hydrogen bonding between lipids was observed to serve as the basis of interlipid complexation. It is deduced from our results and previous studies that dipalmitoylphosphatidylcholine alone is less likely to form interlipid complexes than in the presence of bound ions or other bilayer "impurities" such as dipalmitoylphosphatidylserine. The binding of counterions is observed and quantitated. Based upon the calculated ion binding constants, the Gouy-Chapman surface potential (theta) is calculated. In addition we calculated the electrostatic potential profile (Phi) by twice integrating the system charge distribution. A large discrepancy between and the value of Phi at the membrane surface is observed. However, at "larger" distance from the bilayer surface, a qualitative similarity in the z-profiles of Phi and psi(GC) is seen. The discrepancy between the two potential profiles near the bilayer surface is attributed to the discrete and nonbulk-like nature of water in the interfacial region and to the complex geometry of this region.

Molecular dynamics modelling of EGCG clusters on ceramide bilayers

Energy Technology Data Exchange (ETDEWEB)

Yeo, Jingjie; Cheng, Yuan; Li, Weifeng; Zhang, Yong-Wei [Institute of High Performance Computing, A*STAR, 138632 (Singapore)

2015-12-31

A novel method of atomistic modelling and characterization of both pure ceramide and mixed lipid bilayers is being developed, using only the General Amber ForceField. Lipid bilayers modelled as pure ceramides adopt hexagonal packing after equilibration, and the area per lipid and bilayer thickness are consistent with previously reported theoretical results. Mixed lipid bilayers are modelled as a combination of ceramides, cholesterol, and free fatty acids. This model is shown to be stable after equilibration. Green tea extract, also known as epigallocatechin-3-gallate, is introduced as a spherical cluster on the surface of the mixed lipid bilayer. It is demonstrated that the cluster is able to bind to the bilayers as a cluster without diffusing into the surrounding water.

Structure and hydration of membranes embedded with voltage-sensing domains.

Science.gov (United States)

Krepkiy, Dmitriy; Mihailescu, Mihaela; Freites, J Alfredo; Schow, Eric V; Worcester, David L; Gawrisch, Klaus; Tobias, Douglas J; White, Stephen H; Swartz, Kenton J

2009-11-26

Despite the growing number of atomic-resolution membrane protein structures, direct structural information about proteins in their native membrane environment is scarce. This problem is particularly relevant in the case of the highly charged S1-S4 voltage-sensing domains responsible for nerve impulses, where interactions with the lipid bilayer are critical for the function of voltage-activated ion channels. Here we use neutron diffraction, solid-state nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations to investigate the structure and hydration of bilayer membranes containing S1-S4 voltage-sensing domains. Our results show that voltage sensors adopt transmembrane orientations and cause a modest reshaping of the surrounding lipid bilayer, and that water molecules intimately interact with the protein within the membrane. These structural findings indicate that voltage sensors have evolved to interact with the lipid membrane while keeping energetic and structural perturbations to a minimum, and that water penetrates the membrane, to hydrate charged residues and shape the transmembrane electric field.

Lipid bilayer-coated mesoporous silica nanoparticles carrying bovine hemoglobin towards an erythrocyte mimic.

Science.gov (United States)

Tu, Jing; Bussmann, Jeroen; Du, Guangsheng; Gao, Yue; Bouwstra, Joke A; Kros, Alexander

2018-05-30

Hemoglobin (Hb)-loaded mesoporous silica nanoparticles (MSNs) coated with a lipid bilayer (LB-MSNs) were investigated as an erythrocyte mimic. MSNs with a large average pore size (10 nm) act as a rigid core and provide a protective environment for Hb encapsulated inside the pores. The colloidal stability of Hb-loaded MSNs was enhanced upon the application of a lipid bilayer, through fusion of PEGylated liposomes onto the exterior surface of Hb-loaded MSNs. The morphology and mesostructure of the MSNs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and surface area analysis. The Hb loading capacity (mg/g) in MSNs was studied by thermogravimetric analysis (TGA). UV-Vis absorption spectroscopy revealed that Hb inside MSNs had an identical, but slightly broadened peak in the Soret region compared to free Hb. Furthermore the encapsulated Hb exhibits similar peroxidase-like activity in catalyzing the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) with hydrogen peroxide. The introduction of a supported lipid bilayer (LB) demonstrated the potential to prevent premature Hb release (the burst release decreased from 25.50 ± 0.33% to 6.73 ± 0.83%) and increased the colloidal stability of the Hb-loaded MSNs (hydrodynamic diameter remained ∼250 nm for at least one week). The in vivo systemic circulation and biodistribution of LB-MSNs were studied in optically transparent zebrafish embryos, revealing that LB-MSNs have the potential to act as an erythrocyte mimic in transfusion therapy. Copyright © 2018 Elsevier B.V. All rights reserved.

The radiation effects on lipid bilayers

International Nuclear Information System (INIS)

Ikigai, Hajime; Matsuura, Tomio; Narita, Noboru; Ozawa, Atsushi.

1980-01-01

The Radiation effects on lipid bilayers are studied by the electron spin resonance. Egg lecithin liposomes and human erythrocytes are labeled with spin probes (5 SAL, 12 SAL). Effects of membrane fluidity by X-Ray (or ultraviolet) irradiation are measured by change of the order parameter S. The results obtained are as follows: 1) A similar tendency is observed on the order parameter S between X-Ray irradiated egg lecithin liposomes and human erythrocytes. 2) The rapid changes of the membrane fluidity are observed below 1 krad. The fluctuation of membrane fluidity decreases above 1 krad, consequently the membrane has a tendency changing to a rigid state at low dose area. 3) It is suggested that the more effective radicals are hydroxyl radicals and superoxide radicals. 4) The effects of ultraviolet irradiation with hydrogen peroxide show that hydroxyl radicals lead to changes of membrane fluidity. (author)

A QCM-D study of the concentration- and time-dependent interactions of human LL37 with model mammalian lipid bilayers.

Science.gov (United States)

Lozeau, Lindsay D; Rolle, Marsha W; Camesano, Terri A

2018-07-01

The human antimicrobial peptide LL37 is promising as an alternative to antibiotics due to its biophysical interactions with charged bacterial lipids. However, its clinical potential is limited due to its interactions with zwitterionic mammalian lipids leading to cytotoxicity. Mechanistic insight into the LL37 interactions with mammalian lipids may enable rational design of less toxic LL37-based therapeutics. To this end, we studied concentration- and time-dependent interactions of LL37 with zwitterionic model phosphatidylcholine (PC) bilayers with quartz crystal microbalance with dissipation (QCM-D). LL37 mass adsorption and PC bilayer viscoelasticity changes were monitored by measuring changes in frequency (Δf) and dissipation (ΔD), respectively. The Voigt-Kelvin viscoelastic model was applied to Δf and ΔD to study changes in bilayer thickness and density with LL37 concentration. At low concentrations (0.10-1.00 μM), LL37 adsorbed onto bilayers in a concentration-dependent manner. Further analyses of Δf, ΔD and thickness revealed that peptide saturation on the bilayers was a threshold for interactions observed above 2.00 μM, interactions that were rapid, multi-step, and reached equilibrium in a concentration- and time-dependent manner. Based on these data, we proposed a model of stable transmembrane pore formation at 2.00-10.0 μM, or transition from a primarily lipid to a primarily protein film with a transmembrane pore formation intermediate state at concentrations of LL37 > 10 μM. The concentration-dependent interactions between LL37 and PC bilayers correlated with the observed concentration-dependent biological activities of LL37 (antimicrobial, immunomodulatory and non-cytotoxic at 0.1-1.0 μM, hemolytic and some cytotoxicity at 2.0-13 μM and cytotoxic at >13 μM). Copyright © 2018 Elsevier B.V. All rights reserved.

Lipid diffusion in the distal and proximal leaflets of supported lipid bilayer membranes studied by single particle tracking

Science.gov (United States)

Schoch, Rafael L.; Barel, Itay; Brown, Frank L. H.; Haran, Gilad

2018-03-01

Supported lipid bilayers (SLBs) have been studied extensively as simple but powerful models for cellular membranes. Yet, potential differences in the dynamics of the two leaflets of a SLB remain poorly understood. Here, using single particle tracking, we obtain a detailed picture of bilayer dynamics. We observe two clearly separate diffusing populations, fast and slow, that we associate with motion in the distal and proximal leaflets of the SLB, respectively, based on fluorescence quenching experiments. We estimate diffusion coefficients using standard techniques as well as a new method based on the blur of images due to motion. Fitting the observed diffusion coefficients to a two-leaflet membrane hydrodynamic model allows for the simultaneous determination of the intermonolayer friction coefficient and the substrate-membrane friction coefficient, without any prior assumptions on the strengths of the relevant interactions. Remarkably, our calculations suggest that the viscosity of the interfacial water confined between the membrane and the substrate is elevated by ˜104 as compared to bulk water. Using hidden Markov model analysis, we then obtain insight into the transbilayer movement of lipids. We find that lipid flip-flop dynamics are very fast, with half times in the range of seconds. Importantly, we find little evidence for membrane defect mediated lipid flip-flop for SLBs at temperatures well above the solid-to-liquid transition, though defects seem to be involved when the SLBs are cooled down. Our work thus shows that the combination of single particle tracking and advanced hydrodynamic modeling provides a powerful means to obtain insight into membrane dynamics.

The interaction of M13 coat protein with lipid bilayers : a spectroscopic study

NARCIS (Netherlands)

Sanders, J.C.

1992-01-01

In this thesis a small part of the reproductive cycle of the M13 bacteriophage is studied in more detail, namely the interaction of the major coat protein (MW 5240) with lipid bilayers. During the infection process is the major coat protein of M13 bacteriophage stored in the cytoplasm

The impact of resveratrol in lipid bilayers

DEFF Research Database (Denmark)

Shen, Chen; Ghellinck, Alexis de; Fragneto, Giovanna

The natural antioxidant resveratrol, contained in the skin of grape and accordingly in red wine, has significant health effects such as cardiovascular protection and anti-oxidation. Clinical trials of resveratrol as prophylactic or even therapeutic drug are ongoing. Most probably, the working...... mechanism is unspecific. However, there are only few biophysical studies regarding the impact of resveratrol on lipid membranes. Here, results from a neutron reflectometry investigation on solid supported di-palmitoyl-phosphatidyl-choline (DPPC) bilayers with incorporated resveratrol are presented. The data...... show an accumulation of resveratrol in between the headgroups and evidence its absence in the hydrophobic core. Without a removal mechanism, the headgroup region hosts up to ~25 mol% of resveratrol. The presence of resveratrol induces a change of the tilt angle of the PC headgroups to a more upright...

Absorption and folding of melittin onto lipid bilayer membranes via unbiased atomic detail microsecond molecular dynamics simulation.

Science.gov (United States)

Chen, Charles H; Wiedman, Gregory; Khan, Ayesha; Ulmschneider, Martin B

2014-09-01

Unbiased molecular simulation is a powerful tool to study the atomic details driving functional structural changes or folding pathways of highly fluid systems, which present great challenges experimentally. Here we apply unbiased long-timescale molecular dynamics simulation to study the ab initio folding and partitioning of melittin, a template amphiphilic membrane active peptide. The simulations reveal that the peptide binds strongly to the lipid bilayer in an unstructured configuration. Interfacial folding results in a localized bilayer deformation. Akin to purely hydrophobic transmembrane segments the surface bound native helical conformer is highly resistant against thermal denaturation. Circular dichroism spectroscopy experiments confirm the strong binding and thermostability of the peptide. The study highlights the utility of molecular dynamics simulations for studying transient mechanisms in fluid lipid bilayer systems. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova. Copyright © 2014. Published by Elsevier B.V.

Thermal response of domains in cardiolipin content bilayers

Energy Technology Data Exchange (ETDEWEB)

Domenech, Oscar [Departament de Quimica-Fisica, Facultat de Quimica, U.B. 08028 (Spain); Morros, Antoni [Unitat de Biofisica, Departament de Bioquimica i Biologia Molecular, Facultat de Medicina (Spain); Servei de Ressonancia Magnetica Nuclear (SeRMN), U.A.B., 08193 Bellaterra, Barcelona (Spain); Cabanas, Miquel E. [Servei de Ressonancia Magnetica Nuclear (SeRMN), U.A.B., 08193 Bellaterra, Barcelona (Spain); Montero, M. Teresa [Departament de Fisicoquimica, Facultat de Farmacia, U.B. 08028 (Spain); Hernandez-Borrell, Jordi [Departament de Fisicoquimica, Facultat de Farmacia, U.B. 08028 (Spain)], E-mail: jordihernandezborrell@ub.edu

2007-10-15

In the study described here, supported planar bilayers (SPBs) of 1-palmitoy-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE):cardiolipin (CL) (0.8:0.2, mol/mol) were examined using atomic force microscopy (AFM). SPBs were formed from suspensions of POPE:CL (0.8:0.2, mol/mol) in inverted hexagonal (H{sub II}) phases (buffer containing Ca{sup 2+}). Three laterally segregated domains which differ in height were observed at 24 degC. Based on the area accounted for each domain and the nominal composition of the mixture, we interpret that the higher domain is formed by CL, while the intermediate and lower domains (LDs) are formed by POPE. The three domains respond to temperature increase with relative changes in their area. At 37 degC, we observed that the increase in the area of the intermediate domain occurs at the expense of the LD. {sup 31}P-nuclear magnetic resonance ({sup 31}P-NMR) and Differential scanning calorimetry (DSC) were used in combination with AFM to characterize the phase behavior of the suspensions and to elucidate the nature of the structures observed.

Vesicle fusion with bilayer lipid membrane controlled by electrostatic interaction

Directory of Open Access Journals (Sweden)

Azusa Oshima

2017-09-01

Full Text Available The fusion of proteoliposomes is a promising approach for incorporating membrane proteins in artificial lipid membranes. In this study, we employed an electrostatic interaction between vesicles and supported bilayer lipid membranes (s-BLMs to control the fusion process. We combined large unilamellar vesicles (LUVs containing anionic lipids, which we used instead of proteoliposomes, and s-BLMs containing cationic lipids to control electrostatic interaction. Anionic LUVs were never adsorbed or ruptured on the SiO2 substrate with a slight negative charge, and selectively fused with cationic s-BLMs. The LUVs can be fused effectively to the target position. Furthermore, as the vesicle fusion proceeds and some of the positive charges are neutralized, the attractive interaction weakens and finally the vesicle fusion saturates. In other words, we can control the number of LUVs fused with s-BLMs by controlling the concentration of the cationic lipids in the s-BLMs. The fluidity of the s-BLMs after vesicle fusion was confirmed to be sufficiently high. This indicates that the LUVs attached to the s-BLMs were almost completely fused, and there were few intermediate state vesicles in the fusion process. We could control the position and amount of vesicle fusion with the s-BLMs by employing an electrostatic interaction.

Interactions of inertial cavitation bubbles with stratum corneum lipid bilayers during low-frequency sonophoresis.

Science.gov (United States)

Tezel, Ahmet; Mitragotri, Samir

2003-12-01

Interactions of acoustic cavitation bubbles with biological tissues play an important role in biomedical applications of ultrasound. Acoustic cavitation plays a particularly important role in enhancing transdermal transport of macromolecules, thereby offering a noninvasive mode of drug delivery (sonophoresis). Ultrasound-enhanced transdermal transport is mediated by inertial cavitation, where collapses of cavitation bubbles microscopically disrupt the lipid bilayers of the stratum corneum. In this study, we describe a theoretical analysis of the interactions of cavitation bubbles with the stratum corneum lipid bilayers. Three modes of bubble-stratum corneum interactions including shock wave emission, microjet penetration into the stratum corneum, and impact of microjet on the stratum corneum are considered. By relating the mechanical effects of these events on the stratum corneum structure, the relationship between the number of cavitation events and collapse pressures with experimentally measured increase in skin permeability was established. Theoretical predictions were compared to experimentally measured parameters of cavitation events.

Sensing voltage across lipid membranes

Science.gov (United States)

Swartz, Kenton J.

2009-01-01

The detection of electrical potentials across lipid bilayers by specialized membrane proteins is required for many fundamental cellular processes such as the generation and propagation of nerve impulses. These membrane proteins possess modular voltage-sensing domains, a notable example being the S1-S4 domains of voltage-activated ion channels. Ground-breaking structural studies on these domains explain how voltage sensors are designed and reveal important interactions with the surrounding lipid membrane. Although further structures are needed to fully understand the conformational changes that occur during voltage sensing, the available data help to frame several key concepts that are fundamental to the mechanism of voltage sensing. PMID:19092925

Membrane Protein Mobility and Orientation Preserved in Supported Bilayers Created Directly from Cell Plasma Membrane Blebs.

Science.gov (United States)

Richards, Mark J; Hsia, Chih-Yun; Singh, Rohit R; Haider, Huma; Kumpf, Julia; Kawate, Toshimitsu; Daniel, Susan

2016-03-29

Membrane protein interactions with lipids are crucial for their native biological behavior, yet traditional characterization methods are often carried out on purified protein in the absence of lipids. We present a simple method to transfer membrane proteins expressed in mammalian cells to an assay-friendly, cushioned, supported lipid bilayer platform using cell blebs as an intermediate. Cell blebs, expressing either GPI-linked yellow fluorescent proteins or neon-green fused transmembrane P2X2 receptors, were induced to rupture on glass surfaces using PEGylated lipid vesicles, which resulted in planar supported membranes with over 50% mobility for multipass transmembrane proteins and over 90% for GPI-linked proteins. Fluorescent proteins were tracked, and their diffusion in supported bilayers characterized, using single molecule tracking and moment scaling spectrum (MSS) analysis. Diffusion was characterized for individual proteins as either free or confined, revealing details of the local lipid membrane heterogeneity surrounding the protein. A particularly useful result of our bilayer formation process is the protein orientation in the supported planar bilayer. For both the GPI-linked and transmembrane proteins used here, an enzymatic assay revealed that protein orientation in the planar bilayer results in the extracellular domains facing toward the bulk, and that the dominant mode of bleb rupture is via the "parachute" mechanism. Mobility, orientation, and preservation of the native lipid environment of the proteins using cell blebs offers advantages over proteoliposome reconstitution or disrupted cell membrane preparations, which necessarily result in significant scrambling of protein orientation and typically immobilized membrane proteins in SLBs. The bleb-based bilayer platform presented here is an important step toward integrating membrane proteomic studies on chip, especially for future studies aimed at understanding fundamental effects of lipid interactions

Under the influence of alcohol: The effect of ethanol and methanol on lipid bilayers

NARCIS (Netherlands)

Patra, M.; Salonen, E.; Terama, E.; Vattulainen, I.; Faller, R.; Lee, B.W.; Holopainen, J.M.; Karttunen, M.E.J.

2006-01-01

Extensive microscopic molecular dynamics simulations have been performed to study the effects of short-chain alcohols, methanol and ethanol, on two different fully hydrated lipid bilayer systems (POPC and DPPC) in the fluid phase at 323 K. It is found that ethanol has a stronger effect on the

Data supporting beta-amyloid dimer structural transitions and protein–lipid interactions on asymmetric lipid bilayer surfaces using MD simulations on experimentally derived NMR protein structures

Directory of Open Access Journals (Sweden)

Sara Y. Cheng

2016-06-01

Full Text Available This data article supports the research article entitled “Maximally Asymmetric Transbilayer Distribution of Anionic Lipids Alters the Structure and interaction with Lipids of an Amyloidogenic Protein Dimer Bound to the Membrane Surface” [1]. We describe supporting data on the binding kinetics, time evolution of secondary structure, and residue-contact maps of a surface-absorbed beta-amyloid dimer protein on different membrane surfaces. We further demonstrate the sorting of annular and non-annular regions of the protein/lipid bilayer simulation systems, and the correlation of lipid-number mismatch and surface area per lipid mismatch of asymmetric lipid membranes.

DSC and EPR investigations on effects of cholesterol component on molecular interactions between paclitaxel and phospholipid within lipid bilayer membrane.

Science.gov (United States)

Zhao, Lingyun; Feng, Si-Shen; Kocherginsky, Nikolai; Kostetski, Iouri

2007-06-29

Differential scanning calorimetry (DSC) and electron paramagnetic resonance spectroscopy (EPR) were applied to investigate effects of cholesterol component on molecular interactions between paclitaxel, which is one of the best antineoplastic agents found from nature, and dipalmitoylphosphatidylcholine (DPPC) within lipid bilayer vesicles (liposomes), which could also be used as a model cell membrane. DSC analysis showed that incorporation of paclitaxel into the DPPC bilayer causes a reduction in the cooperativity of bilayer phase transition, leading to a looser and more flexible bilayer structure. Including cholesterol component in the DPPC/paclitaxel mixed bilayer can facilitate the molecular interaction between paclitaxel and lipid and make the tertiary system more stable. EPR analysis demonstrated that both of paclitaxel and cholesterol have fluidization effect on the DPPC bilayer membranes although cholesterol has more significant effect than paclitaxel does. The reduction kinetics of nitroxides by ascorbic acid showed that paclitaxel can inhibit the reaction by blocking the diffusion of either the ascorbic acid or nitroxide molecules since the reaction is tested to be a first order one. Cholesterol can remarkably increase the reduction reaction speed. This research may provide useful information for optimizing liposomal formulation of the drug as well as for understanding the pharmacology of paclitaxel.

Impact of monoolein on aquaporin1-based supported lipid bilayer membranes

International Nuclear Information System (INIS)

Wang, Zhining; Wang, Xida; Ding, Wande; Wang, Miaoqi; Gao, Congjie; Qi, Xin

2015-01-01

Aquaporin (AQP) based biomimetic membranes have attracted considerable attention for their potential water purification applications. In this paper, AQP1 incorporated biomimetic membranes were prepared and characterized. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), infrared absorption spectroscopy, fluorescence microscopy, and contact angle measurements. The nanofiltration performance of the AQP1 incorporated membranes was investigated at 4 bar by using 2 g l −1 NaCl as feed solution. Lipid mobility plays an important role in the performance of the AQP1 incorporated supported lipid bilayer (SLB) membranes. We demonstrated that the lipid mobility is successfully tuned by the addition of monoolein (MO). Through in situ AFM and fluorescence recovery after photo-bleaching (FRAP) measurements, the membrane morphology and the molecular mobility were studied. The lipid mobility increased in the sequence DPPC < DPPC/MO (R MO = 5/5) < DOPC/MO (R MO = 5/5) < DOPC, which is consistent with the flux increment and salt rejection. This study may provide some useful insights for improving the water purification performance of biomimetic membranes. (paper)

Parvovirus B19 VLP recognizes globoside in supported lipid bilayers.

Science.gov (United States)

Nasir, Waqas; Nilsson, Jonas; Olofsson, Sigvard; Bally, Marta; Rydell, Gustaf E

2014-05-01

Studies have suggested that the glycosphingolipid globoside (Gb4Cer) is a receptor for human parvovirus B19. Virus-like particles bind to Gb4Cer on thin-layer chromatograms, but a direct interaction between the virus and lipid membrane-associated Gb4Cer has been debated. Here, we characterized the binding of parvovirus B19 VP1/VP2 virus-like particles to glycosphingolipids (i) on thin-layer chromatograms (TLCs) and (ii) incorporated into supported lipid bilayers (SLBs) acting as cell-membrane mimics. The binding specificities of parvovirus B19 determined in the two systems were in good agreement; the VLP recognized both Gb4Cer and the Forssman glycosphingolipid on TLCs and in SLBs compatible with the role of Gb4Cer as a receptor for this virus. Copyright © 2014 Elsevier Inc. All rights reserved.

Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles

DEFF Research Database (Denmark)

Bagatolli, Luis; Needham, David

2014-01-01

to study composition-structure-property materials relationships of free-standing lipid bilayer membranes. Because their size (~5 to 100 m diameter) that is well above the resolution limit of regular light microscopes, GUVs are suitable membrane models for optical microscopy and micromanipulation...

Comparative structural analysis of lipid binding START domains.

Directory of Open Access Journals (Sweden)

Ann-Gerd Thorsell

Full Text Available Steroidogenic acute regulatory (StAR protein related lipid transfer (START domains are small globular modules that form a cavity where lipids and lipid hormones bind. These domains can transport ligands to facilitate lipid exchange between biological membranes, and they have been postulated to modulate the activity of other domains of the protein in response to ligand binding. More than a dozen human genes encode START domains, and several of them are implicated in a disease.We report crystal structures of the human STARD1, STARD5, STARD13 and STARD14 lipid transfer domains. These represent four of the six functional classes of START domains.Sequence alignments based on these and previously reported crystal structures define the structural determinants of human START domains, both those related to structural framework and those involved in ligand specificity.This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1.

Study of pH (low) insertion peptides (pHLIPs) interaction with lipid bilayer of membrane

Science.gov (United States)

Weerakkody, Dhammika

The pH-dependent interactions of pHLIPsRTM (pH (Low) Insertion Peptides) with lipid bilayer of membrane provides an opportunity to study and address fundamental questions of protein folding/insertion into membrane and unfolding/exit, as well as develop novel approach to target acidic diseased tissue such as cancer, ischemic myocardium, infection and others. The main goal of the work presented here is to answer the following questions: - What is the molecular mechanism of spontaneous insertion and folding of a peptide in a lipid bilayer of membrane; - What is the molecular mechanism of unfolding and exit of a peptide from a lipid bilayer of membrane; - How polar cargo attached to a peptide's inserting end might affect the process of insertion into a lipid bilayer of membrane; How sequence variation will affect a peptide's interactions with a lipid bilayer of membrane (partitioning into bilayer at neutral and low pH; apparent pK of insertion) with the main goal to identify the best pHLIP variants for imaging and therapy of pathological states such as cancer and others. It has been demonstrated that pHLIP insertion into a membrane is associated with the protonation of Asp/Glu residues, which leads to an increase of hydrophobicity that triggers the folding and insertion of the peptide across a lipid bilayer. The insertion of the pHLIP is unidirectional and it is accompanied by the release of energy. Therefore, the energy of membrane associated-folding can be used to favor the movement of cell-impermeable polar cargo molecules across the hydrophobic membrane bilayer when they are attached to the inserting end of pHLIP. Both pH-targeting behavior and molecular translocation have been demonstrated in cultured cells and in vivo. Thus, there is an opportunity to develop a novel concept in drug delivery, which is based on the use of a monomeric, pH-sensitive peptide molecular transporter, to deliver agents that are significantly more polar than conventional drugs

Membrane-Sculpting BAR Domains Generate Stable Lipid Microdomains

Science.gov (United States)

Zhao, Hongxia; Michelot, Alphée; Koskela, Essi V.; Tkach, Vadym; Stamou, Dimitrios; Drubin, David G.; Lappalainen, Pekka

2014-01-01

SUMMARY Bin-Amphiphysin-Rvs (BAR) domain proteins are central regulators of many cellular processes involving membrane dynamics. BAR domains sculpt phosphoinositide-rich membranes to generate membrane protrusions or invaginations. Here, we report that, in addition to regulating membrane geometry, BAR domains can generate extremely stable lipid microdomains by “freezing” phosphoinositide dynamics. This is a general feature of BAR domains, because the yeast endocytic BAR and Fes/CIP4 homology BAR (F-BAR) domains, the inverse BAR domain of Pinkbar, and the eisosomal BAR protein Lsp1 induced phosphoinositide clustering and halted lipid diffusion, despite differences in mechanisms of membrane interactions. Lsp1 displays comparable low diffusion rates in vitro and in vivo, suggesting that BAR domain proteins also generate stable phosphoinositide microdomains in cells. These results uncover a conserved role for BAR superfamily proteins in regulating lipid dynamics within membranes. Stable microdomains induced by BAR domain scaffolds and specific lipids can generate phase boundaries and diffusion barriers, which may have profound impacts on diverse cellular processes. PMID:24055060

Synthesis of new piroxicam derivatives and their influence on lipid bilayers.

Science.gov (United States)

Szczęśniak-Sięga, Berenika; Maniewska, Jadwiga; Poła, Andrzej; Środa-Pomianek, Kamila; Malinka, Wiesław; Michalak, Krystyna

2014-01-01

A novel series of potentially biologically active 1,2-benzothiazine 1,1-dioxides--analogs of piroxicam (a recognized non-steroidal anti-inflammatory drug) were synthesized from commercially available saccharin. All of the synthesized compounds were subjected to preliminary evaluation for their ability to interact with lipid bilayers. The influence of the new derivatives of piroxicam on liposomes made of EYPC was investigated by fluorescence spectroscopy with two fluorescent probes--Laurdan and Prodan. All the studied compounds showed an interaction with model membranes.

Atomic force microscope image contrast mechanisms on supported lipid bilayers.

Science.gov (United States)

Schneider, J; Dufrêne, Y F; Barger, W R; Lee, G U

2000-08-01

This work presents a methodology to measure and quantitatively interpret force curves on supported lipid bilayers in water. We then use this method to correlate topographic imaging contrast in atomic force microscopy (AFM) images of phase-separated Langmuir-Blodgett bilayers with imaging load. Force curves collected on pure monolayers of both distearoylphosphatidylethanolamine (DSPE) and monogalactosylethanolamine (MGDG) and dioleoylethanolamine (DOPE) deposited at similar surface pressures onto a monolayer of DSPE show an abrupt breakthrough event at a repeatable, material-dependent force. The breakthrough force for DSPE and MGDG is sizable, whereas the breakthrough force for DOPE is too small to measure accurately. Contact-mode AFM images on 1:1 mixed monolayers of DSPE/DOPE and MGDG/DOPE have a high topographic contrast at loads between the breakthrough force of each phase, and a low topographic contrast at loads above the breakthrough force of both phases. Frictional contrast is inverted and magnified at loads above the breakthrough force of both phases. These results emphasize the important role that surface forces and mechanics can play in imaging multicomponent biomembranes with AFM.

Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

DEFF Research Database (Denmark)

Rønnest, A. K.; Peters, Günther H.J.; Hansen, Flemming Yssing

2016-01-01

Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid...... compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have...... the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic...

Modeling the Effects of Lipid Composition on Stratum Corneum Bilayers Using Molecular Dynamics Simulations

Science.gov (United States)

Huzil, J. Torin; Sivaloganathan, Siv; Kohandel, Mohammad; Foldvari, Marianna

2011-11-01

The advancement of dermal and transdermal drug delivery requires the development of delivery systems that are suitable for large protein and nucleic acid-based therapeutic agents. However, a complete mechanistic understanding of the physical barrier properties associated with the epidermis, specifically the membrane structures within the stratum corneum, has yet to be developed. Here, we describe the assembly and computational modeling of stratum corneum lipid bilayers constructed from varying ratios of their constituent lipids (ceramide, free fatty acids and cholesterol) to determine if there is a difference in the physical properties of stratum corneum compositions.

Poly(aniline) nanowires in sol-gel coated ITO: A pH-responsive substrate for planar supported lipid bilayers

Science.gov (United States)

Ge, Chenhao; Orosz, Kristina S.; Armstrong, Neal R.; Saavedra, S. Scott

2011-01-01

Facilitated ion transport across an artificial lipid bilayer coupled to a solid substrate is a function common to several types of bioelectronic devices based on supported membranes, including biomimetic fuel cells and ion channel biosensors. Described here is fabrication of a pH-sensitive transducer composed of a porous sol-gel layer derivatized with poly(aniline) (PANI) nanowires grown from an underlying planar indium-tin oxide (ITO) electrode. The upper sol-gel surface is hydrophilic, smooth, and compatible with deposition of a planar supported lipid bilayer (PSLB) formed via vesicle fusion. Conducting tip AFM was used to show that the PANI wires are connected to the ITO, which convert this electrode into a potentiometric pH sensor. The response to changes in the pH of the buffer contacting the PANI nanowire/sol-gel/ITO electrode is blocked by the very low ion permeability of the overlying, fluid PSLB. The feasibility of using this assembly to monitor facilitated proton transport across the PSLB was demonstrated by doping the membrane with lipophilic ionophores that respond to a transmembrane pH gradient, which produced an apparent proton permeability several orders of magnitude greater than values measured for undoped lipid bilayers. PMID:21707069

Supported lipid bilayer on nanocrystalline diamond: dual optical and field-effect sensor for membrane disruption

Czech Academy of Sciences Publication Activity Database

Ang, P.K.; Loh, K.P.; Wohland, T.; Nesládek, Miloš; Van Hove, E.

2009-01-01

Roč. 19, č. 1 (2009), s. 109-116 ISSN 1616-301X Institutional research plan: CEZ:AV0Z10100520 Keywords : nanocrystalline diamond * biocompatibility * supported lipid bilayers * biosensors * solution gate field effect transistor Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 6.990, year: 2009

Influences of the Structure of Lipids on Thermal Stability of Lipid Membranes

International Nuclear Information System (INIS)

Hai Nan-Nan; Zhou Xin; Li Ming

2015-01-01

The binding free energy (BFE) of lipid to lipid bilayer is a critical factor to determine the thermal or mechanical stability of the bilayer. Although the molecular structure of lipids has significant impacts on BFE of the lipid, there lacks a systematic study on this issue. In this paper we use coarse-grained molecular dynamics simulation to investigate this problem for several typical phospholipids. We find that both the tail length and tail unsaturation can significantly affect the BFE of lipids but in opposite way, namely, BFE decreases linearly with increasing length, but increases linearly with addition of unsaturated bonds. Inspired by the specific structure of cholesterol which is a crucial component of biomembrane, we also find that introduction of carbo-ring-like structures to the lipid tail or to the bilayer may greatly enhance the stability of the bilayer. Our simulation also shows that temperature can influence the bilayer stability and this effect can be significant when the bilayer undergoes phase transition. These results may be helpful to the design of liposome or other self-assembled lipid systems. (paper)

Spatial orientation and electric-field-driven transport of hypericin inside of bilayer lipid membranes.

Science.gov (United States)

Strejčková, Alena; Staničová, Jana; Jancura, Daniel; Miškovský, Pavol; Bánó, Gregor

2013-02-07

Fluorescence experiments were carried out to investigate the interaction of hypericin (Hyp), a natural hydrophobic photosensitizer, with artificial bilayer lipid membranes. The spatial orientation of Hyp monomers incorporated in diphytanoyl phosphatidylcholine (DPhPC) membranes was determined by measuring the dependence of the Hyp fluorescence intensity on the angle of incidence of p- and s-polarized excitation laser beams. Inside of the membrane, Hyp monomers are preferentially located in the layers near the membrane/water interface and are oriented with the S(1) ← S(0) transition dipole moments perpendicular to the membrane surface. Transport of Hyp anions between the two opposite sides of the lipid bilayer was induced by applying rectangular electric field pulses to the membrane. The characteristic time for Hyp transport through the membrane center was evaluated by the analysis of the Hyp fluorescence signal during the voltage pulses. In the zero-voltage limit, the transport time approached 70 ms and gradually decreased with higher voltage applied to the membrane. In addition, our measurements indicated an apparent pK(a) constant of 8 for Hyp deprotonation in the membrane.

Perillyl alcohol: Dynamic interactions with the lipid bilayer and implications for long‐term inhalational chemotherapy for gliomas

DEFF Research Database (Denmark)

Orlando da Fonseca, Clovis; Khandelia, Himanshu; D’Alincourt Salazar, Marcela

2016-01-01

at the outer plasma membrane interface are critical for effective drug uptake. Amphipathic molecules such as perillyl alcohol (POH) have a high partition coefficient and generally lead to altered lipid acyl tail dynamics near the lipid-water interface, impacting the lipid bilayer structure and transport...... of patients with LGG halted disease progression with virtually no toxicity. Conclusion: Altogether, the results suggest that POH-induced alterations of the plasma membrane might be contributing to its therapeutic efficacy in preventing LGG progression....

Wafer-scale fabrication of glass-FEP-glass microfluidic devices for lipid bilayer experiments.

Science.gov (United States)

Bomer, Johan G; Prokofyev, Alexander V; van den Berg, Albert; Le Gac, Séverine

2014-12-07

We report a wafer-scale fabrication process for the production of glass-FEP-glass microdevices using UV-curable adhesive (NOA81) as gluing material, which is applied using a novel "spin & roll" approach. Devices are characterized for the uniformity of the gluing layer, presence of glue in the microchannels, and alignment precision. Experiments on lipid bilayers with electrophysiological recordings using a model pore-forming polypeptide are demonstrated.

Dispersion of fullerenes in phospholipid bilayers and the subsequent phase changes in the host bilayers

Energy Technology Data Exchange (ETDEWEB)

Jeng, U-S. [National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan (China)]. E-mail: usjeng@nsrrc.org.tw; Hsu, C.-H. [National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan (China); Lin, T.-L. [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Wu, C.-M. [Department of Chemical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Chen, H.-L. [Department of Chemical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Tai, L.-A. [Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Hwang, K.-C. [Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2005-02-28

We have studied the structure and phase transition characteristics of the fullerenes (C{sub 60})-embedded lipid bilayers. With small-angle neutron scattering (SANS), we have observed a degradation of bilayer ordering and a suppression effect on the phase transitions of the host vesicle bilayers of dipalmitoylphosphatidylcholine (DPPC), due to the embedment of fullerenes. The fullerene-embedded lipid system with substrate-oriented bilayers is also investigated using X-ray reflectivity and grazing incident small-angle X-ray scattering (GISAXS). In the depth direction, the multilamellar peaks observed in the X-ray reflectivity profile for the oriented DPPC/C{sub 60} bilayers reveal a larger head-to-head distance D{sub HH} of 50.6 A and a bilayer spacing D of 59.8 A, compared to the D{sub HH}=47.7 A and D=59.5 A for a pure DPPC membrane measured at the same conditions. Furthermore, the lipid head layers and water layers in the extracted electron density profile for the complex system are highly smeared, implying a fluctuating or corrugated structure in this zone. Correspondingly, GISAXS for the oriented DPPC/C{sub 60} membrane reveals stronger diffuse scatterings along the membrane plane than that for the pure DPPC system, indicating a higher in-plane correlation associated with the embedded fullerenes.

Comparative computational study of interaction of C60-fullerene and tris-malonyl-C60-fullerene isomers with lipid bilayer: relation to their antioxidant effect.

Directory of Open Access Journals (Sweden)

Marine E Bozdaganyan

Full Text Available Oxidative stress induced by excessive production of reactive oxygen species (ROS has been implicated in the etiology of many human diseases. It has been reported that fullerenes and some of their derivatives-carboxyfullerenes-exhibits a strong free radical scavenging capacity. The permeation of C60-fullerene and its amphiphilic derivatives-C3-tris-malonic-C60-fullerene (C3 and D3-tris-malonyl-C60-fullerene (D3-through a lipid bilayer mimicking the eukaryotic cell membrane was studied using molecular dynamics (MD simulations. The free energy profiles along the normal to the bilayer composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC for C60, C3 and D3 were calculated. We found that C60 molecules alone or in clusters spontaneously translocate to the hydrophobic core of the membrane and stay inside the bilayer during the whole period of simulation time. The incorporation of cluster of fullerenes inside the bilayer changes properties of the bilayer and leads to its deformation. In simulations of the tris-malonic fullerenes we discovered that both isomers, C3 and D3, adsorb at the surface of the bilayer but only C3 tends to be buried in the area of the lipid headgroups forming hydrophobic contacts with the lipid tails. We hypothesize that such position has implications for ROS scavenging mechanism in the specific cell compartments.

Lipid Microarray Biosensor for Biotoxin Detection.

Energy Technology Data Exchange (ETDEWEB)

Singh, Anup K.; Throckmorton, Daniel J.; Moran-Mirabal, Jose C.; Edel, Joshua B.; Meyer, Grant D.; Craighead, Harold G.

2006-05-01

We present the use of micron-sized lipid domains, patterned onto planar substrates and within microfluidic channels, to assay the binding of bacterial toxins via total internal reflection fluorescence microscopy (TIRFM). The lipid domains were patterned using a polymer lift-off technique and consisted of ganglioside-populated DSPC:cholesterol supported lipid bilayers (SLBs). Lipid patterns were formed on the substrates by vesicle fusion followed by polymer lift-off, which revealed micron-sized SLBs containing either ganglioside GT1b or GM1. The ganglioside-populated SLB arrays were then exposed to either Cholera toxin subunit B (CTB) or Tetanus toxin fragment C (TTC). Binding was assayed on planar substrates by TIRFM down to 1 nM concentration for CTB and 100 nM for TTC. Apparent binding constants extracted from three different models applied to the binding curves suggest that binding of a protein to a lipid-based receptor is strongly affected by the lipid composition of the SLB and by the substrate on which the bilayer is formed. Patterning of SLBs inside microfluidic channels also allowed the preparation of lipid domains with different compositions on a single device. Arrays within microfluidic channels were used to achieve segregation and selective binding from a binary mixture of the toxin fragments in one device. The binding and segregation within the microfluidic channels was assayed with epifluorescence as proof of concept. We propose that the method used for patterning the lipid microarrays on planar substrates and within microfluidic channels can be easily adapted to proteins or nucleic acids and can be used for biosensor applications and cell stimulation assays under different flow conditions. KEYWORDS. Microarray, ganglioside, polymer lift-off, cholera toxin, tetanus toxin, TIRFM, binding constant.4

Phase Behavior and Domain Size in Sphingomyelin-Containing Lipid Bilayers

Science.gov (United States)

Petruzielo, Robin S.; Heberle, Frederick A.; Drazba, Paul; Katsaras, John; Feigenson, Gerald W.

2013-01-01

Membrane raft size measurements are crucial to understanding the stability and functionality of rafts in cells. The challenge of accurately measuring raft size is evidenced by the disparate reports of domain sizes, which range from nanometers to microns for the ternary model membrane system sphingomyelin (SM)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (Chol). Using Förster resonance energy transfer (FRET) and differential scanning calorimetry (DSC), we established phase diagrams for porcine brain SM (bSM)/dioleoyl-sn-glycero-3-phosphocholine (DOPC)/Chol and bSM/POPC/Chol at 15 and 25°C. By combining two techniques with different spatial sensitivities, namely FRET and small-angle neutron scattering (SANS), we have significantly narrowed the uncertainty in domain size estimates for bSM/POPC/Chol mixtures. Compositional trends in FRET data revealed coexisting domains at 15 and 25°C for both mixtures, while SANS measurements detected no domain formation for bSM/POPC/Chol. Together these results indicate that liquid domains in bSM/POPC/Chol are between 2 and 7 nm in radius at 25°C: that is, domains must be on the order of the 2–6 nm Förster distance of the FRET probes, but smaller than the ~7 nm minimum cluster size detectable with SANS. However, for palmitoyl SM (PSM)/POPC/Chol at a similar composition, SANS detected coexisting liquid domains. This increase in domain size upon replacing the natural SM component (which consists of a mixture of chain lengths) with synthetic PSM, suggests a role for SM chain length in modulating raft size in vivo. PMID:23337475

Yeast lipids can phase separate into micrometer-scale membrane domains

DEFF Research Database (Denmark)

Klose, Christian; Ejsing, Christer S; Garcia-Saez, Ana J

2010-01-01

The lipid raft concept proposes that biological membranes have the potential to form functional domains based on a selective interaction between sphingolipids and sterols. These domains seem to be involved in signal transduction and vesicular sorting of proteins and lipids. Although there is bioc......The lipid raft concept proposes that biological membranes have the potential to form functional domains based on a selective interaction between sphingolipids and sterols. These domains seem to be involved in signal transduction and vesicular sorting of proteins and lipids. Although...... there is biochemical evidence for lipid raft-dependent protein and lipid sorting in the yeast Saccharomyces cerevisiae, direct evidence for an interaction between yeast sphingolipids and the yeast sterol ergosterol, resulting in membrane domain formation, is lacking. Here we show that model membranes formed from yeast...... total lipid extracts possess an inherent self-organization potential resulting in Ld-Lo phase coexistence at physiologically relevant temperature. Analyses of lipid extracts from mutants defective in sphingolipid metabolism as well as reconstitution of purified yeast lipids in model membranes of defined...

Engineering plant membranes using droplet interface bilayers.

Science.gov (United States)

Barlow, N E; Smpokou, E; Friddin, M S; Macey, R; Gould, I R; Turnbull, C; Flemming, A J; Brooks, N J; Ces, O; Barter, L M C

2017-03-01

Droplet interface bilayers (DIBs) have become widely recognised as a robust platform for constructing model membranes and are emerging as a key technology for the bottom-up assembly of synthetic cell-like and tissue-like structures. DIBs are formed when lipid-monolayer coated water droplets are brought together inside a well of oil, which is excluded from the interface as the DIB forms. The unique features of the system, compared to traditional approaches (e.g., supported lipid bilayers, black lipid membranes, and liposomes), is the ability to engineer multi-layered bilayer networks by connecting multiple droplets together in 3D, and the capability to impart bilayer asymmetry freely within these droplet architectures by supplying droplets with different lipids. Yet despite these achievements, one potential limitation of the technology is that DIBs formed from biologically relevant components have not been well studied. This could limit the reach of the platform to biological systems where bilayer composition and asymmetry are understood to play a key role. Herein, we address this issue by reporting the assembly of asymmetric DIBs designed to replicate the plasma membrane compositions of three different plant species; Arabidopsis thaliana , tobacco, and oats, by engineering vesicles with different amounts of plant phospholipids, sterols and cerebrosides for the first time. We show that vesicles made from our plant lipid formulations are stable and can be used to assemble asymmetric plant DIBs. We verify this using a bilayer permeation assay, from which we extract values for absolute effective bilayer permeation and bilayer stability. Our results confirm that stable DIBs can be assembled from our plant membrane mimics and could lead to new approaches for assembling model systems to study membrane translocation and to screen new agrochemicals in plants.

Interactions of Inertial Cavitation Bubbles with Stratum Corneum Lipid Bilayers during Low-Frequency Sonophoresis

OpenAIRE

Tezel, Ahmet; Mitragotri, Samir

2003-01-01

Interactions of acoustic cavitation bubbles with biological tissues play an important role in biomedical applications of ultrasound. Acoustic cavitation plays a particularly important role in enhancing transdermal transport of macromolecules, thereby offering a noninvasive mode of drug delivery (sonophoresis). Ultrasound-enhanced transdermal transport is mediated by inertial cavitation, where collapses of cavitation bubbles microscopically disrupt the lipid bilayers of the stratum corneum. In...

Influence of the state of phase of lipid bilayer on the exposure of glucose residues on the surface of liposomes.

Science.gov (United States)

Villalva, Denise Gradella; Giansanti, Luisa; Mauceri, Alessandro; Ceccacci, Francesca; Mancini, Giovanna

2017-11-01

The presence of carbohydrate-binding proteins (i.e. lectins) on the surface of various bacterial strains and their overexpression in some tumor tissues makes the use of glycosylated liposomes a promising approach for the specific drug delivery in antibacterial and anti-cancer therapies. However, the functionalization of liposome surface with sugar moieties by glycosylated amphiphiles does not ensure the binding of sugar-coated vesicles with lectins. In fact, the composition and properties of lipid bilayer play a pivotal role in the exposure of sugar residues and in the interaction with lectins. The influence of the length of the hydrophilic spacer that links the sugar to liposome surface and of the presence of saturated or unsaturated phospholipids in the lipid bilayer on the ability of glucosylated liposomes to interact with a model lectin, Concanavalin A, was investigated. Our results demonstrate that both the chain length and the prensece of unsaturation, parameters that strongly affect the fluidity of the lipid bilayer, affect agglutination. In particular, agglutination is favored when liposomes are in the gel phase within a defined range of temperature. Moreover, the obtained results confirm that the length of the PEG spacer, that influences both lipid organization and the exposure of sugar moieties to the bulk, plays a crucial role in liposome/lectin interaction. Copyright © 2017 Elsevier B.V. All rights reserved.

Microchemical device based on microscopic bilayer lipid membranes; Bisho 2 bunshimaku wo mochiiita maikuro kagaku debaisu

Energy Technology Data Exchange (ETDEWEB)

Yokoyama, H. [Electrotechnical Lab., Ibaraki (Japan)

1996-04-01

If an organism is regarded as a macromolecular system, the element device to construct the same is the molecular structure of nano meter scale formed by the functional protein existing in biomembranes. A lot of essential functions of organism such as the sense reception including vision, gustation, etc., photosynthesis, energy-substance production and so on are performed therein. In this paper, the structure, preparing process and the functions of the microchemical device using micro-bilipid membranes are described. The simulation of the sense receiving functions of organisms is tried by said microchemical device wherein, same as biomembranes, the base is bilayer lipid molecular membrane and the receptive protein for receiving signals from exterior and output molecules such as ion channels connected to said receptive protein and the like are incorporated in the membranes. Recently, it becomes possible to make a partial imaging of the bilayer lipid membranes fixed on porous membrane by the observation with scanning Maxwell-stress microscope. 4 refs., 3 figs.

Nitriles at Silica Interfaces Resemble Supported Lipid Bilayers.

Science.gov (United States)

Berne, Bruce J; Fourkas, John T; Walker, Robert A; Weeks, John D

2016-09-20

Nitriles are important solvents not just for bulk reactions but also for interfacial processes such as separations, heterogeneous catalysis, and electrochemistry. Although nitriles have a polar end and a lipophilic end, the cyano group is not hydrophilic enough for these substances to be thought of as prototypical amphiphiles. This picture is now changing, as research is revealing that at a silica surface nitriles can organize into structures that, in many ways, resemble lipid bilayers. This unexpected organization may be a key component of unique interfacial behavior of nitriles that make them the solvents of choice for so many applications. The first hints of this lipid-bilayer-like (LBL) organization of nitriles at silica interfaces came from optical Kerr effect (OKE) experiments on liquid acetonitrile confined in the pores of sol-gel glasses. The orientational dynamics revealed by OKE spectroscopy suggested that the confined liquid is composed of a relatively immobile sublayer of molecules that accept hydrogen bonds from the surface silanol groups and an interdigitated, antiparallel layer that is capable of exchanging into the centers of the pores. This picture of acetonitrile has been borne out by molecular dynamics simulations and vibrational sum-frequency generation (VSFG) experiments. Remarkably, these simulations further indicate that the LBL organization is repeated with increasing disorder at least 20 Å into the liquid from a flat silica surface. Simulations and VSFG and OKE experiments indicate that extending the alkyl chain to an ethyl group leads to the formation of even more tightly packed LBL organization featuring entangled alkyl tails. When the alkyl portion of the molecule is a bulky t-butyl group, packing constraints prevent well-ordered LBL organization of the liquid. In each case, the surface-induced organization of the liquid is reflected in its interfacial dynamics. Acetonitrile/water mixtures are favored solvent systems for separations

Alpha-helical hydrophobic polypeptides form proton-selective channels in lipid bilayers

Science.gov (United States)

Oliver, A. E.; Deamer, D. W.

1994-01-01

Proton translocation is important in membrane-mediated processes such as ATP-dependent proton pumps, ATP synthesis, bacteriorhodopsin, and cytochrome oxidase function. The fundamental mechanism, however, is poorly understood. To test the theoretical possibility that bundles of hydrophobic alpha-helices could provide a low energy pathway for ion translocation through the lipid bilayer, polyamino acids were incorporated into extruded liposomes and planar lipid membranes, and proton translocation was measured. Liposomes with incorporated long-chain poly-L-alanine or poly-L-leucine were found to have proton permeability coefficients 5 to 7 times greater than control liposomes, whereas short-chain polyamino acids had relatively little effect. Potassium permeability was not increased markedly by any of the polyamino acids tested. Analytical thin layer chromatography measurements of lipid content and a fluorescamine assay for amino acids showed that there were approximately 135 polyleucine or 65 polyalanine molecules associated with each liposome. Fourier transform infrared spectroscopy indicated that a major fraction of the long-chain hydrophobic peptides existed in an alpha-helical conformation. Single-channel recording in both 0.1 N HCl and 0.1 M KCl was also used to determine whether proton-conducting channels formed in planar lipid membranes (phosphatidylcholine/phosphatidylethanolamine, 1:1). Poly-L-leucine and poly-L-alanine in HCl caused a 10- to 30-fold increase in frequency of conductive events compared to that seen in KCl or by the other polyamino acids in either solution. This finding correlates well with the liposome observations in which these two polyamino acids caused the largest increase in membrane proton permeability but had little effect on potassium permeability. Poly-L-leucine was considerably more conductive than poly-L-alanine due primarily to larger event amplitudes and, to a lesser extent, a higher event frequency. Poly-L-leucine caused two

Optical stretching as a tool to investigate the mechanical properties of lipid bilayers.

Science.gov (United States)

Solmaz, Mehmet E; Sankhagowit, Shalene; Biswas, Roshni; Mejia, Camilo A; Povinelli, Michelle L; Malmstadt, Noah

2013-10-07

Measurements of lipid bilayer bending modulus by various techniques produce widely divergent results. We attempt to resolve some of this ambiguity by measuring bending modulus in a system that can rapidly process large numbers of samples, yielding population statistics. This system is based on optical stretching of giant unilamellar vesicles (GUVs) in a microfluidic dual-beam optical trap (DBOT). The microfluidic DBOT system is used here to measure three populations of GUVs with distinct lipid compositions. We find that gel-phase membranes are significantly stiffer than liquid-phase membranes, consistent with previous reports. We also find that the addition of cholesterol does not alter the bending modulus of membranes composed of a monounsaturated phospholipid.

Molecular Interaction of a New Antibacterial Polymer with a Supported Lipid Bilayer Measured by an in situ Label-Free Optical Technique

Directory of Open Access Journals (Sweden)

Robert Horvath

2013-05-01

Full Text Available The interaction of the antibacterial polymer–branched poly(ethylene imine substituted with quaternary ammonium groups, PEO and alkyl chains, PEI25QI5J5A815–with a solid supported lipid bilayer was investigated using surface sensitive optical waveguide spectroscopy. The analysis of the optogeometrical parameters was extended developing a new composite layer model in which the structural and optical anisotropy of the molecular layers was taken into consideration. Following in situ the change of optical birefringence we were able to determine the composition of the lipid/polymer surface layer as well as the displacement of lipid bilayer by the antibacterial polymer without using additional labeling. Comparative assessment of the data of layer thickness and optical anisotropy helps to reveal the molecular mechanism of antibacterial effect of the polymer investigated.

Evaluating Force Fields for the Computational Prediction of Ionized Arginine and Lysine Side-Chains Partitioning into Lipid Bilayers and Octanol.

Science.gov (United States)

Sun, Delin; Forsman, Jan; Woodward, Clifford E

2015-04-14

Abundant peptides and proteins containing arginine (Arg) and lysine (Lys) amino acids can apparently permeate cell membranes with ease. However, the mechanisms by which these peptides and proteins succeed in traversing the free energy barrier imposed by cell membranes remain largely unestablished. Precise thermodynamic studies (both theoretical and experimental) on the interactions of Arg and Lys residues with model lipid bilayers can provide valuable clues to the efficacy of these cationic peptides and proteins. We have carried out molecular dynamics simulations to calculate the interactions of ionized Arg and Lys side-chains with the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer for 10 widely used lipid/protein force fields: CHARMM36/CHARMM36, SLIPID/AMBER99SB-ILDN, OPLS-AA/OPLS-AA, Berger/OPLS-AA, Berger/GROMOS87, Berger/GROMOS53A6, GROMOS53A6/GROMOS53A6, nonpolarizable MARTINI, polarizable MARTINI, and BMW MARTINI. We performed umbrella sampling simulations to obtain the potential of mean force for Arg and Lys side-chains partitioning from water to the bilayer interior. We found significant differences between the force fields, both for the interactions between side-chains and bilayer surface, as well as the free energy cost for placing the side-chain at the center of the bilayer. These simulation results were compared with the Wimley-White interfacial scale. We also calculated the free energy cost for transferring ionized Arg and Lys side-chains from water to both dry and wet octanol. Our simulations reveal rapid diffusion of water molecules into octanol whereby the equilibrium mole fraction of water in the wet octanol phase was ∼25%. Surprisingly, our free energy calculations found that the high water content in wet octanol lowered the water-to-octanol partitioning free energies for cationic residues by only 0.6 to 0.7 kcal/mol.

Alpha-tocopherol inhibits pore formation in oxidized bilayers

NARCIS (Netherlands)

Boonnoy, P.; Karttunen, M.; Wong-Ekkabut, J.

2017-01-01

In biological membranes, alpha-tocopherols (α-toc; vitamin E) protect polyunsaturated lipids from free radicals. Although the interactions of α-toc with non-oxidized lipid bilayers have been studied, their effects on oxidized bilayers remain unknown. In this study, atomistic molecular dynamics (MD)

Compositional and structural characterization of monolayers and bilayers composed of native pulmonary surfactant from wild type mice

DEFF Research Database (Denmark)

Bernardino de la Serna, Jorge; Hansen, Soren; Berzina, Zane

2013-01-01

spectrometry experiments were also performed in order to obtain relevant information on the lipid composition of this material. Bilayers composed of mice pulmonary surfactant showed coexistence of distinct domains at room temperature, with morphologies and lateral packing resembling the coexistence of liquid...

Fabrication and characterization of an integrated ionic device from suspended polypyrrole and alamethicin-reconstituted lipid bilayer membranes

International Nuclear Information System (INIS)

Northcutt, Robert; Sundaresan, Vishnu-Baba

2012-01-01

Conducting polymers are electroactive materials that undergo conformal relaxation of the polymer backbone in the presence of an electrical field through ion exchange with solid or aqueous electrolytes. This conformal relaxation and the associated morphological changes make conducting polymers highly suitable for actuation and sensing applications. Among smart materials, bioderived active materials also use ion transport for sensing and actuation functions via selective ion transport. The transporter proteins extracted from biological cell membranes and reconstituted into a bilayer lipid membrane in bioderived active materials regulate ion transport for engineering functions. The protein transporter reconstituted in the bilayer lipid membrane is referred to as the bioderived membrane and serves as the active component in bioderived active materials. Inspired by the similarities in the physics of transduction in conducting polymers and bioderived active materials, an integrated ionic device is formed from the bioderived membrane and the conducting polymer membrane. This ionic device is fabricated into a laminated thin-film membrane and a common ion that can be processed by the bioderived and the conducting polymer membranes couple the ionic function of these two membranes. An integrated ionic device, fabricated from polypyrrole (PPy) doped with sodium dodecylbenzenesulfonate (NaDBS) and an alamethicin-reconstituted DPhPC bilayer lipid membrane, is presented in this paper. A voltage-gated sodium current regulates the electrochemical response in the PPy(DBS) layer. The integrated device is fabricated on silicon-based substrates through microfabrication, electropolymerization, and vesicle fusion, and ionic activity is characterized through electrochemical measurements. (paper)

Alamethicin in lipid bilayers: combined use of X-ray scattering and MD simulations.

Science.gov (United States)

Pan, Jianjun; Tieleman, D Peter; Nagle, John F; Kucerka, Norbert; Tristram-Nagle, Stephanie

2009-06-01

We study fully hydrated bilayers of two di-monounsaturated phospholipids diC18:1PC (DOPC) and diC22:1PC with varying amounts of alamethicin (Alm). We combine the use of X-ray diffuse scattering and molecular dynamics simulations to determine the orientation of alamethicin in model lipids. Comparison of the experimental and simulated form factors shows that Alm helices are inserted transmembrane at high humidity and high concentrations, in agreement with earlier results. The X-ray scattering data and the MD simulations agree that membrane thickness changes very little up to 1/10 Alm/DOPC. In contrast, the X-ray data indicate that the thicker diC22:1PC membrane thins with added Alm, a total decrease in thickness of 4 A at 1/10 Alm/diC22:1PC. The different effect of Alm on the thickness changes of the two bilayers is consistent with Alm having a hydrophobic thickness close to the hydrophobic thickness of 27 A for DOPC; Alm is then mismatched with the 7 A thicker diC22:1PC bilayer. The X-ray data indicate that Alm decreases the bending modulus (K(C)) by a factor of approximately 2 in DOPC and a factor of approximately 10 in diC22:1PC membranes (P/L approximately 1/10). The van der Waals and fluctuational interactions between bilayers are also evaluated through determination of the anisotropic B compressibility modulus.

Conformational Plasticity of the Influenza A M2 Transmembrane Helix in Lipid Bilayers Under Varying pH, Drug Binding and Membrane Thickness

Science.gov (United States)

Hu, Fanghao; Luo, Wenbin; Cady, Sarah D.; Hong, Mei

2010-01-01

Membrane proteins change their conformations to respond to environmental cues, thus conformational plasticity is important for function. The influenza A M2 protein forms an acid-activated proton channel important for the virus lifecycle. Here we have used solid-state NMR spectroscopy to examine the conformational plasticity of membrane-bound transmembrane domain of M2 (M2TM). 13C and 15N chemical shifts indicate coupled conformational changes of several pore-facing residues due to changes in bilayer thickness, drug binding and pH. The structural changes are attributed to the formation of a well-defined helical kink at G34 in the drug-bound state and in thick lipid bilayers, non-ideal backbone conformation of the secondary-gate residue V27 in the presence of drug, and non-ideal conformation of the proton-sensing residue H37 at high pH. The chemical shifts constrained the (ϕ, ψ) torsion angles for three basis states, the equilibrium among which explains the multiple resonances per site in the NMR spectra under different combinations of bilayer thickness, drug binding and pH conditions. Thus, conformational plasticity is important for the proton conduction and inhibition of M2TM. The study illustrates the utility of NMR chemical shifts for probing the structural plasticity and folding of membrane proteins. PMID:20883664

Membrane and Protein Interactions of the Pleckstrin Homology Domain Superfamily

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Marc Lenoir

2015-10-01

Full Text Available The human genome encodes about 285 proteins that contain at least one annotated pleckstrin homology (PH domain. As the first phosphoinositide binding module domain to be discovered, the PH domain recruits diverse protein architectures to cellular membranes. PH domains constitute one of the largest protein superfamilies, and have diverged to regulate many different signaling proteins and modules such as Dbl homology (DH and Tec homology (TH domains. The ligands of approximately 70 PH domains have been validated by binding assays and complexed structures, allowing meaningful extrapolation across the entire superfamily. Here the Membrane Optimal Docking Area (MODA program is used at a genome-wide level to identify all membrane docking PH structures and map their lipid-binding determinants. In addition to the linear sequence motifs which are employed for phosphoinositide recognition, the three dimensional structural features that allow peripheral membrane domains to approach and insert into the bilayer are pinpointed and can be predicted ab initio. The analysis shows that conserved structural surfaces distinguish which PH domains associate with membrane from those that do not. Moreover, the results indicate that lipid-binding PH domains can be classified into different functional subgroups based on the type of membrane insertion elements they project towards the bilayer.

Membrane and Protein Interactions of the Pleckstrin Homology Domain Superfamily.

Science.gov (United States)

Lenoir, Marc; Kufareva, Irina; Abagyan, Ruben; Overduin, Michael

2015-10-23

The human genome encodes about 285 proteins that contain at least one annotated pleckstrin homology (PH) domain. As the first phosphoinositide binding module domain to be discovered, the PH domain recruits diverse protein architectures to cellular membranes. PH domains constitute one of the largest protein superfamilies, and have diverged to regulate many different signaling proteins and modules such as Dbl homology (DH) and Tec homology (TH) domains. The ligands of approximately 70 PH domains have been validated by binding assays and complexed structures, allowing meaningful extrapolation across the entire superfamily. Here the Membrane Optimal Docking Area (MODA) program is used at a genome-wide level to identify all membrane docking PH structures and map their lipid-binding determinants. In addition to the linear sequence motifs which are employed for phosphoinositide recognition, the three dimensional structural features that allow peripheral membrane domains to approach and insert into the bilayer are pinpointed and can be predicted ab initio. The analysis shows that conserved structural surfaces distinguish which PH domains associate with membrane from those that do not. Moreover, the results indicate that lipid-binding PH domains can be classified into different functional subgroups based on the type of membrane insertion elements they project towards the bilayer.

Lipid self-assembly and lectin-induced reorganization of the plasma membrane.

Science.gov (United States)

Sych, Taras; Mély, Yves; Römer, Winfried

2018-05-26

The plasma membrane represents an outstanding example of self-organization in biology. It plays a vital role in protecting the integrity of the cell interior and regulates meticulously the import and export of diverse substances. Its major building blocks are proteins and lipids, which self-assemble to a fluid lipid bilayer driven mainly by hydrophobic forces. Even if the plasma membrane appears-globally speaking-homogeneous at physiological temperatures, the existence of specialized nano- to micrometre-sized domains of raft-type character within cellular and synthetic membrane systems has been reported. It is hypothesized that these domains are the origin of a plethora of cellular processes, such as signalling or vesicular trafficking. This review intends to highlight the driving forces of lipid self-assembly into a bilayer membrane and the formation of small, transient domains within the plasma membrane. The mechanisms of self-assembly depend on several factors, such as the lipid composition of the membrane and the geometry of lipids. Moreover, the dynamics and organization of glycosphingolipids into nanometre-sized clusters will be discussed, also in the context of multivalent lectins, which cluster several glycosphingolipid receptor molecules and thus create an asymmetric stress between the two membrane leaflets, leading to tubular plasma membrane invaginations.This article is part of the theme issue 'Self-organization in cell biology'. © 2018 The Author(s).

The Integrin Receptor in Biologically Relevant Bilayers

DEFF Research Database (Denmark)

Kalli, Antreas C.; Róg, Tomasz; Vattulainen, Ilpo

2017-01-01

/talin complex was inserted in biologically relevant bilayers that resemble the cell plasma membrane containing zwitterionic and charged phospholipids, cholesterol and sphingolipids to study the dynamics of the integrin receptor and its effect on bilayer structure and dynamics. The results of this study...... demonstrate the dynamic nature of the integrin receptor and suggest that the presence of the integrin receptor alters the lipid organization between the two leaflets of the bilayer. In particular, our results suggest elevated density of cholesterol and of phosphatidylserine lipids around the integrin....../talin complex and a slowing down of lipids in an annulus of ~30 Å around the protein due to interactions between the lipids and the integrin/talin F2–F3 complex. This may in part regulate the interactions of integrins with other related proteins or integrin clustering thus facilitating signal transduction...

Organization of fluorescent cholesterol analogs in lipid bilayers - lessons from cyclodextrin extraction.

Science.gov (United States)

Milles, Sigrid; Meyer, Thomas; Scheidt, Holger A; Schwarzer, Roland; Thomas, Lars; Marek, Magdalena; Szente, Lajos; Bittman, Robert; Herrmann, Andreas; Günther Pomorski, Thomas; Huster, Daniel; Müller, Peter

2013-08-01

To characterize the structure and dynamics of cholesterol in membranes, fluorescent analogs of the native molecule have widely been employed. The cholesterol content in membranes is in general manipulated by using water-soluble cyclodextrins. Since the interactions between cyclodextrins and fluorescent-labeled cholesterol have not been investigated in detail so far, we have compared the cyclodextrin-mediated membrane extraction of three different fluorescent cholesterol analogs (one bearing a NBD and two bearing BODIPY moieties). Extraction of these analogs was followed by measuring the Förster resonance energy transfer between a rhodamine moiety linked to phosphatidylethanolamine and the labeled cholesterol. The extraction kinetics revealed that the analogs are differently extracted from membranes. We examined the orientation of the analogs within the membrane and their influence on lipid condensation using NMR and EPR spectroscopies. Our data indicate that the extraction of fluorescent sterols from membranes is determined by several parameters, including their impact on lipid order, their hydrophobicity, their intermolecular interactions with surrounding lipids, their orientation within the bilayer, and their affinity with the exogenous acceptor. Copyright © 2013 Elsevier B.V. All rights reserved.

Interaction of elaiophylin with model bilayer membrane

Science.gov (United States)

Genova, J.; Dencheva-Zarkova, M.

2017-01-01

Elaiophylin is a new macrodiolide antibiotic, which is produced by the Streptomyces strains [1]. It displays biological activities against Gram-positive bacteria and fungi. The mode of action of this antibiotic has been attributed to an alteration of the membrane permeability. When this antibiotic is inserted into the bilayer membranes destabilization of the membrane and formation of ion-penetrable channels is observed. The macrodiolide antibiotic forms stable cation selective ion channels in synthetic lipid bilayer membranes. The aim of this work was to study the interactions of Elaiophylin with model bilayer membranes and to get information on the mechanical properties of lipid bilayers in presence of this antibiotic. Patch-clamp technique [2] were used in the study

Potential and limitations of S-layers as support for planar lipid bilayers

International Nuclear Information System (INIS)

Kiene, E.

2011-01-01

A huge step in the development of life was most certainly the formation of lipid membranes and the resulting possibility for generating confined volumes, structurally discrete from the environment. Yet, communication had to be maintained with the outside world, so these membrane borders were populated with functional units, like membrane receptors and transporters, enabling the exchange of material, energy and information. Therefore, from a scientific point of view, the requirement for analysis platforms for membrane proteins incorporated into model membrane scaffolds emerged. The membrane systems hosting arbitrary membrane proteins are desired to unite the features of stability and fluidity and to provide a quasi natural environment for the membrane proteins in order to maintain their structure and function. In the current state of the art there are hardly any relevant fluid membrane models, which is why in this project a prokaryotic protein-lipid architecture was mimicked as a promising supportive system for biological membranes. A large number of bacteria and archaea envelope their outer cell membrane with a proteinaceous lattice, the so-called surface- or S-layer. The present work deals with S-layer protein lattices as a support for anchored lipid bilayers. S-layer proteins show the intrinsic ability to self-assemble into periodically structured, two-dimensional patterns with a porous character. Genetic or chemical modification of the proteinaceous crystal layers can provide regularly spread binding moieties for functionalised lipids as components of a lipid membrane. In this project, a wildtype S-layer (SbpA from L. sphaericus exhibiting p4 lattice symmetry) was chemically activated to provide anchors for amino-functionalised lipids; and in a genetic approach a recombinant, HIS-tagged derivative was used for attracting Ni-functionalised lipids. The latter method seemed a more elegant way of lipid binding, since the anchoring regions were more regularly spread

Membrane-sculpting BAR domains generate stable lipid microdomains

DEFF Research Database (Denmark)

Zhao, Hongxia; Michelot, Alphée; Koskela, Essi V.

2013-01-01

Bin-Amphiphysin-Rvs (BAR) domain proteins are central regulators of many cellular processes involving membrane dynamics. BAR domains sculpt phosphoinositide-rich membranes to generate membrane protrusions or invaginations. Here, we report that, in addition to regulating membrane geometry, BAR...... domains can generate extremely stable lipid microdomains by "freezing" phosphoinositide dynamics. This is a general feature of BAR domains, because the yeast endocytic BAR and Fes/CIP4 homology BAR (F-BAR) domains, the inverse BAR domain of Pinkbar, and the eisosomal BAR protein Lsp1 induced...... phosphoinositide clustering and halted lipid diffusion, despite differences in mechanisms of membrane interactions. Lsp1 displays comparable low diffusion rates in vitro and in vivo, suggesting that BAR domain proteins also generate stable phosphoinositide microdomains in cells. These results uncover a conserved...

The action of polyene antibiotics on lipid bilayer membranes in the presence of several cations and anions

NARCIS (Netherlands)

Zutphen, H. van; Demel, R.A.; Norman, A.W.; Deenen, L.L.M. van

1971-01-01

1. 1. Filipin complex, filipin II, filipin III, nystatin, etruscomycin, and pimaricin at concentrations of 10−5 M were able to disrupt bimolecular lipid films containing lecithin and cholesterol in a 1:1 molar ratio. 2. 2. The above antibiotics were not able to disrupt lecithin bilayer

Systematic implicit solvent coarse-graining of bilayer membranes: lipid and phase transferability of the force field

Energy Technology Data Exchange (ETDEWEB)

Wang Zunjing; Deserno, Markus, E-mail: zwang@cmu.ed, E-mail: deserno@andrew.cmu.ed [Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States)

2010-09-15

We study the lipid and phase transferability of our recently developed systematically coarse-grained solvent-free membrane model. The force field was explicitly parameterized to describe a fluid 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer at 310 K with correct structure and area per lipid, while gaining at least three orders of magnitude in computational efficiency (see Wang and Deserno 2010 J. Phys. Chem. B 114 11207-20). Here, we show that exchanging CG tails, without any subsequent re-parameterization, creates reliable models of 1,2-dioleoylphosphatidylcholine (DOPC) and 1,2-dipalmitoylphosphatidylcholine (DPPC) lipids in terms of structure and area per lipid. Furthermore, all CG lipids undergo a liquid-gel transition upon cooling, with characteristics like those observed in experiments and all-atom simulations during phase transformation. These studies suggest a promising transferability of our force field parameters to different lipid species and thermodynamic state points, properties that are a prerequisite for even more complex systems, such as mixtures.

Systematic implicit solvent coarse-graining of bilayer membranes: lipid and phase transferability of the force field

International Nuclear Information System (INIS)

Wang Zunjing; Deserno, Markus

2010-01-01

We study the lipid and phase transferability of our recently developed systematically coarse-grained solvent-free membrane model. The force field was explicitly parameterized to describe a fluid 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer at 310 K with correct structure and area per lipid, while gaining at least three orders of magnitude in computational efficiency (see Wang and Deserno 2010 J. Phys. Chem. B 114 11207-20). Here, we show that exchanging CG tails, without any subsequent re-parameterization, creates reliable models of 1,2-dioleoylphosphatidylcholine (DOPC) and 1,2-dipalmitoylphosphatidylcholine (DPPC) lipids in terms of structure and area per lipid. Furthermore, all CG lipids undergo a liquid-gel transition upon cooling, with characteristics like those observed in experiments and all-atom simulations during phase transformation. These studies suggest a promising transferability of our force field parameters to different lipid species and thermodynamic state points, properties that are a prerequisite for even more complex systems, such as mixtures.

Lipid Bilayer Membrane in a Silicon Based Micron Sized Cavity Accessed by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy.

Science.gov (United States)

Khan, Muhammad Shuja; Dosoky, Noura Sayed; Patel, Darayas; Weimer, Jeffrey; Williams, John Dalton

2017-07-05

Supported lipid bilayers (SLBs) are widely used in biophysical research to probe the functionality of biological membranes and to provide diagnoses in high throughput drug screening. Formation of SLBs at below phase transition temperature ( Tm ) has applications in nano-medicine research where low temperature profiles are required. Herein, we report the successful production of SLBs at above-as well as below-the Tm of the lipids in an anisotropically etched, silicon-based micro-cavity. The Si-based cavity walls exhibit controlled temperature which assist in the quick and stable formation of lipid bilayer membranes. Fusion of large unilamellar vesicles was monitored in real time in an aqueous environment inside the Si cavity using atomic force microscopy (AFM), and the lateral organization of the lipid molecules was characterized until the formation of the SLBs. The stability of SLBs produced was also characterized by recording the electrical resistance and the capacitance using electrochemical impedance spectroscopy (EIS). Analysis was done in the frequency regime of 10 -2 -10⁵ Hz at a signal voltage of 100 mV and giga-ohm sealed impedance was obtained continuously over four days. Finally, the cantilever tip in AFM was utilized to estimate the bilayer thickness and to calculate the rupture force at the interface of the tip and the SLB. We anticipate that a silicon-based, micron-sized cavity has the potential to produce highly-stable SLBs below their Tm . The membranes inside the Si cavity could last for several days and allow robust characterization using AFM or EIS. This could be an excellent platform for nanomedicine experiments that require low operating temperatures.

The PH Domain of PDK1 Exhibits a Novel, Phospho-Regulated Monomer-Dimer Equilibrium With Important Implications for Kinase Domain Activation: Single Molecule and Ensemble Studies†

Science.gov (United States)

Ziemba, Brian P.; Pilling, Carissa; Calleja, Véronique; Larijani, Banafshé; Falke, Joseph J.

2013-01-01

Phosphoinositide-Dependent Kinase-1 (PDK1) is an essential master kinase recruited to the plasma membrane by the binding of its C-terminal PH domain to the signaling lipid phosphatidylinositol-3,4-5-trisphosphate (PIP3). Membrane binding leads to PDK1 phospho-activation, but despite the central role of PDK1 in signaling and cancer biology this activation mechanism remains poorly understood. PDK1 has been shown to exist as a dimer in cells, and one crystal structure of its isolated PH domain exhibits a putative dimer interface. It has been proposed that phosphorylation of PH domain residue T513 (or the phospho-mimetic T513E mutation) may regulate a novel PH domain dimer-monomer equilibrium, thereby converting an inactive PDK1 dimer to an active monomer. However, the oligomeric state(s) of the PH domain on the membrane have not yet been determined, nor whether a negative charge at position 513 is sufficient to regulate its oligomeric state. The present study investigates the binding of purified WT and T513E PDK1 PH domains to lipid bilayers containing the PIP3 target lipid, using both single molecule and ensemble measurements. Single molecule analysis of the brightness of fluorescent PH domain shows that the PIP3-bound WT PH domain on membranes is predominantly dimeric, while the PIP3-bound T513E PH domain is monomeric, demonstrating that negative charge at the T513 position is sufficient to dissociate the PH domain dimer and is thus likely to play a central role in PDK1 monomerization and activation. Single molecule analysis of 2-D diffusion of PH domain-PIP3 complexes reveals that the dimeric WT PH domain diffuses at the same rate a single lipid molecule, indicating that only one of its two PIP3 binding sites is occupied and there is little protein penetration into the bilayer as observed for other PH domains. The 2-D diffusion of T513E PH domain is slower, suggesting the negative charge disrupts local structure in a way that enables greater protein insertion into

Assessing the nature of lipid raft membranes

DEFF Research Database (Denmark)

Niemelä, Perttu S; Ollila, Samuli; Hyvönen, Marja T

2007-01-01

of highly ordered lateral domains rich in sphingomyelin and cholesterol (CHOL). These domains, called functional lipid rafts, have been suggested to take part in a variety of dynamic cellular processes such as membrane trafficking, signal transduction, and regulation of the activity of membrane proteins......-scale simulations to elucidate the properties of ternary raft mixtures with CHOL, palmitoylsphingomyelin (PSM), and palmitoyloleoylphosphatidylcholine. We simulate two bilayers of 1,024 lipids for 100 ns in the liquid-ordered phase and one system of the same size in the liquid-disordered phase. The studies provide...... heterogeneity more difficult. The findings reveal aspects of the role of favored (specific) lipid-lipid interactions within rafts and clarify the prominent role of CHOL in altering the properties of the membrane locally in its neighborhood. Also, we show that the presence of PSM and CHOL in rafts leads...

Calculations of the electrostatic potential adjacent to model phospholipid bilayers.

Science.gov (United States)

Peitzsch, R M; Eisenberg, M; Sharp, K A; McLaughlin, S

1995-03-01

We used the nonlinear Poisson-Boltzmann equation to calculate electrostatic potentials in the aqueous phase adjacent to model phospholipid bilayers containing mixtures of zwitterionic lipids (phosphatidylcholine) and acidic lipids (phosphatidylserine or phosphatidylglycerol). The aqueous phase (relative permittivity, epsilon r = 80) contains 0.1 M monovalent salt. When the bilayers contain equipotential surfaces are discrete domes centered over the negatively charged lipids and are approximately twice the value calculated using Debye-Hückel theory. When the bilayers contain > 25% acidic lipid, the -25 mV equipotential profiles are essentially flat and agree well with the values calculated using Gouy-Chapman theory. When the bilayers contain 100% acidic lipid, all of the equipotential surfaces are flat and agree with Gouy-Chapman predictions (including the -100 mV surface, which is located only 1 A from the outermost atoms). Even our model bilayers are not simple systems: the charge on each lipid is distributed over several atoms, these partial charges are non-coplanar, there is a 2 A ion-exclusion region (epsilon r = 80) adjacent to the polar headgroups, and the molecular surface is rough. We investigated the effect of these four factors using smooth (or bumpy) epsilon r = 2 slabs with embedded point charges: these factors had only minor effects on the potential in the aqueous phase.

Scattering Studies of Hydrophobic Monomers in Liposomal Bilayers: An Expanding Shell Model of Monomer Distribution

International Nuclear Information System (INIS)

Richter, Andrew; Dergunov, Sergey; Ganus, Bill; Thomas, Zachary; Pingali, Sai Venkatesh; Urban, Volker S.; Liu, Yun; Porcar, Lionel; Pinkhassik, Eugene

2011-01-01

Hydrophobic monomers partially phase separate from saturated lipids when loaded into lipid bilayers in amounts exceeding a 1:1 monomer/lipid molar ratio. This conclusion is based on the agreement between two independent methods of examining the structure of monomer-loaded bilayers. Complete phase separation of monomers from lipids would result in an increase in bilayer thickness and a slight increase in the diameter of liposomes. A homogeneous distribution of monomers within the bilayer would not change the bilayer thickness and would lead to an increase in the liposome diameter. The increase in bilayer thickness, measured by the combination of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS), was approximately half of what was predicted for complete phase separation. The increase in liposome diameter, measured by dynamic light scattering (DLS), was intermediate between values predicted for a homogeneous distribution and complete phase separation. Combined SANS, SAXS, and DLS data suggest that at a 1.2 monomer/lipid ratio approximately half of the monomers are located in an interstitial layer sandwiched between lipid sheets. These results expand our understanding of using self-assembled bilayers as scaffolds for the directed covalent assembly of organic nanomaterials. In particular, the partial phase separation of monomers from lipids corroborates the successful creation of nanothin polymer materials with uniform imprinted nanopores. Pore-forming templates do not need to span the lipid bilayer to create a pore in the bilayer-templated films.

The ring structure and organization of light harvesting 2 complexes in a reconstituted lipid bilayer, resolved by atomic force microscopy.

Science.gov (United States)

Stamouli, Amalia; Kafi, Sidig; Klein, Dionne C G; Oosterkamp, Tjerk H; Frenken, Joost W M; Cogdell, Richard J; Aartsma, Thijs J

2003-04-01

The main function of the transmembrane light-harvesting complexes in photosynthetic organisms is the absorption of a light quantum and its subsequent rapid transfer to a reaction center where a charge separation occurs. A combination of freeze-thaw and dialysis methods were used to reconstitute the detergent-solubilized Light Harvesting 2 complex (LH2) of the purple bacterium Rhodopseudomonas acidophila strain 10050 into preformed egg phosphatidylcholine liposomes, without the need for extra chemical agents. The LH2-containing liposomes opened up to a flat bilayer, which were imaged with tapping and contact mode atomic force microscopy under ambient and physiological conditions, respectively. The LH2 complexes were packed in quasicrystalline domains. The endoplasmic and periplasmic sides of the LH2 complexes could be distinguished by the difference in height of the protrusions from the lipid bilayer. The results indicate that the complexes entered in intact liposomes. In addition, it was observed that the most hydrophilic side, the periplasmic, enters first in the membrane. In contact mode the molecular structure of the periplasmic side of the transmembrane pigment-protein complex was observed. Using Föster's theory for describing the distance dependent energy transfer, we estimate the dipole strength for energy transfer between two neighboring LH2s, based on the architecture of the imaged unit cell.

A lipid binding domain in sphingosine kinase 2

International Nuclear Information System (INIS)

Don, Anthony S.; Rosen, Hugh

2009-01-01

The lipid second messenger sphingosine 1-phosphate (S1P) is a critical mediator of cellular proliferation and survival signals, and is essential for vasculogenesis and neurogenesis. S1P formation is catalysed by sphingosine kinases 1 and 2 (Sphk1 and Sphk2). We have found that the endogenous glycolipid sulfatide (3-O-sulfogalactosylceramide) binds to and inhibits the activity of Sphk2 and the closely related ceramide kinase (Cerk), but not Sphk1. Using sulfatide as a probe, we mapped the lipid binding domain to the N-terminus of Sphk2 (residues 1-175), a region of sequence that is absent in Sphk1, but aligns with a pleckstrin homology domain in Cerk. Accordingly, Sphk2 bound to phosphatidylinositol monophosphates but not to abundant cellular phospholipids. Deleting the N-terminal domain reduced Sphk2 membrane localisation in cells. We have therefore identified a lipid binding domain in Sphk2 that is important for the enzyme's sub-cellular localisation.

Size and mobility of lipid domains tuned by geometrical constraints.

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Schütte, Ole M; Mey, Ingo; Enderlein, Jörg; Savić, Filip; Geil, Burkhard; Janshoff, Andreas; Steinem, Claudia

2017-07-25

In the plasma membrane of eukaryotic cells, proteins and lipids are organized in clusters, the latter ones often called lipid domains or "lipid rafts." Recent findings highlight the dynamic nature of such domains and the key role of membrane geometry and spatial boundaries. In this study, we used porous substrates with different pore radii to address precisely the extent of the geometric constraint, permitting us to modulate and investigate the size and mobility of lipid domains in phase-separated continuous pore-spanning membranes (PSMs). Fluorescence video microscopy revealed two types of liquid-ordered ( l o ) domains in the freestanding parts of the PSMs: ( i ) immobile domains that were attached to the pore rims and ( ii ) mobile, round-shaped l o domains within the center of the PSMs. Analysis of the diffusion of the mobile l o domains by video microscopy and particle tracking showed that the domains' mobility is slowed down by orders of magnitude compared with the unrestricted case. We attribute the reduced mobility to the geometric confinement of the PSM, because the drag force is increased substantially due to hydrodynamic effects generated by the presence of these boundaries. Our system can serve as an experimental test bed for diffusion of 2D objects in confined geometry. The impact of hydrodynamics on the mobility of enclosed lipid domains can have great implications for the formation and lateral transport of signaling platforms.

Membranes linked by trans-SNARE complexes require lipids prone to non-bilayer structure for progression to fusion.

Science.gov (United States)

Zick, Michael; Stroupe, Christopher; Orr, Amy; Douville, Deborah; Wickner, William T

2014-01-01

Like other intracellular fusion events, the homotypic fusion of yeast vacuoles requires a Rab GTPase, a large Rab effector complex, SNARE proteins which can form a 4-helical bundle, and the SNARE disassembly chaperones Sec17p and Sec18p. In addition to these proteins, specific vacuole lipids are required for efficient fusion in vivo and with the purified organelle. Reconstitution of vacuole fusion with all purified components reveals that high SNARE levels can mask the requirement for a complex mixture of vacuole lipids. At lower, more physiological SNARE levels, neutral lipids with small headgroups that tend to form non-bilayer structures (phosphatidylethanolamine, diacylglycerol, and ergosterol) are essential. Membranes without these three lipids can dock and complete trans-SNARE pairing but cannot rearrange their lipids for fusion. DOI: http://dx.doi.org/10.7554/eLife.01879.001.

Nanodiscs for immobilization of lipid bilayers and membrane receptors: kinetic analysis of cholera toxin binding to a glycolipid receptor

DEFF Research Database (Denmark)

Borch, Jonas; Torta, Federico; Sligar, Stephen G

2008-01-01

nanodiscs and their incorporated membrane receptors can be attached to surface plasmon resonance sensorchips and used to measure the kinetics of the interaction between soluble molecules and membrane receptors inserted in the bilayer of nanodiscs. Cholera toxin and its glycolipid receptor G(M1) constitute...... a system that can be considered a paradigm for interactions of soluble proteins with membrane receptors. In this work, we have investigated different technologies for capturing nanodiscs containing the glycolipid receptor G(M1) in lipid bilayers, enabling measurements of binding of its soluble interaction...

The PH domain of phosphoinositide-dependent kinase-1 exhibits a novel, phospho-regulated monomer-dimer equilibrium with important implications for kinase domain activation: single-molecule and ensemble studies.

Science.gov (United States)

Ziemba, Brian P; Pilling, Carissa; Calleja, Véronique; Larijani, Banafshé; Falke, Joseph J

2013-07-16

Phosphoinositide-dependent kinase-1 (PDK1) is an essential master kinase recruited to the plasma membrane by the binding of its C-terminal PH domain to the signaling lipid phosphatidylinositol-3,4,5-trisphosphate (PIP3). Membrane binding leads to PDK1 phospho-activation, but despite the central role of PDK1 in signaling and cancer biology, this activation mechanism remains poorly understood. PDK1 has been shown to exist as a dimer in cells, and one crystal structure of its isolated PH domain exhibits a putative dimer interface. It has been proposed that phosphorylation of PH domain residue T513 (or the phospho-mimetic T513E mutation) may regulate a novel PH domain dimer-monomer equilibrium, thereby converting an inactive PDK1 dimer to an active monomer. However, the oligomeric states of the PH domain on the membrane have not yet been determined, nor whether a negative charge at position 513 is sufficient to regulate its oligomeric state. This study investigates the binding of purified wild-type (WT) and T513E PDK1 PH domains to lipid bilayers containing the PIP3 target lipid, using both single-molecule and ensemble measurements. Single-molecule analysis of the brightness of the fluorescent PH domain shows that the PIP3-bound WT PH domain on membranes is predominantly dimeric while the PIP3-bound T513E PH domain is monomeric, demonstrating that negative charge at the T513 position is sufficient to dissociate the PH domain dimer and is thus likely to play a central role in PDK1 monomerization and activation. Single-molecule analysis of two-dimensional (2D) diffusion of PH domain-PIP3 complexes reveals that the dimeric WT PH domain diffuses at the same rate as a single lipid molecule, indicating that only one of its two PIP3 binding sites is occupied and there is little penetration of the protein into the bilayer as observed for other PH domains. The 2D diffusion of T513E PH domain is slower, suggesting the negative charge disrupts local structure in a way that allows

Functional reconstitution of rhodopsin into tubular lipid bilayers supported by nanoporous media.

Science.gov (United States)

Soubias, Olivier; Polozov, Ivan V; Teague, Walter E; Yeliseev, Alexei A; Gawrisch, Klaus

2006-12-26

We report on a novel reconstitution method for G-protein-coupled receptors (GPCRs) that yields detergent-free, single, tubular membranes in porous anodic aluminum oxide (AAO) filters at concentrations sufficient for structural studies by solid-state NMR. The tubular membranes line the inner surface of pores that traverse the filters, permitting easy removal of detergents during sample preparation as well as delivery of ligands for functional studies. Reconstitution of bovine rhodopsin into AAO filters did not interfere with rhodopsin function. Photoactivation of rhodopsin in AAO pores, monitored by UV-vis spectrophotometry, was indistinguishable from rhodopsin in unsupported unilamellar liposomes. The rhodopsin in AAO pores is G-protein binding competent as shown by a [35S]GTPgammaS binding assay. The lipid-rhodopsin interaction was investigated by 2H NMR on sn-1- or sn-2-chain perdeuterated 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phospholine as a matrix lipid. Rhodopsin incorporation increased mosaic spread of bilayer orientations and contributed to spectral density of motions with correlation times in the range of nano- to microseconds, detected as a significant reduction in spin-spin relaxation times. The change in lipid chain order parameters due to interaction with rhodopsin was insignificant.

Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene Cores on Self-Assembly Behavior. Part 2: Domain Formation by Self-Assembly in Lipid Bilayer Membranes

Directory of Open Access Journals (Sweden)

Stefan Werner

2017-09-01

Full Text Available Supramolecular self-assembly of membrane constituents within a phospholipid bilayer creates complex functional platforms in biological cells that operate in intracellular signaling, trafficking and membrane remodeling. Synthetic polyphilic compounds of macromolecular or small size can be incorporated into artificial phospholipid bilayers. Featuring three or four moieties of different philicities, they reach beyond ordinary amphiphilicity and open up avenues to new functions and interaction concepts. Here, we have incorporated a series of X-shaped bolapolyphiles into DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayers of giant unilamellar vesicles. The bolapolyphiles consist of a rod-like oligo(phenylene ethynylene (OPE core, hydrophilic glycerol-based headgroups with or without oligo(ethylene oxide expansions at both ends and two lateral alkyl chains attached near the center of the OPE core. In the absence of DPPC and water, the compounds showed thermotropic liquid-crystalline behavior with a transition between polyphilic and amphiphilic assembly (see part 1 in this issue. In DPPC membranes, various trends in the domain morphologies were observed upon structure variations, which entailed branched alkyl chains of various sizes, alkyl chain semiperfluorination and size expansion of the headgroups. Observed effects on domain morphology are interpreted in the context of the bulk behavior (part 1 and of a model that was previously developed based on spectroscopic and physicochemical data.

Adsorption and Orientation of Human Islet Amyloid Polypeptide (hIAPP Monomer at Anionic Lipid Bilayers: Implications for Membrane-Mediated Aggregation

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Guanghong Wei

2013-03-01

Full Text Available Protein misfolding and aggregation cause serious degenerative diseases, such as Alzheimer’s and type II diabetes. Human islet amyloid polypeptide (hIAPP is the major component of amyloid deposits found in the pancreas of type II diabetic patients. Increasing evidence suggests that β-cell death is related to the interaction of hIAPP with the cellular membrane, which accelerates peptide aggregation. In this study, as a first step towards understanding the membrane-mediated hIAPP aggregation, we investigate the atomic details of the initial step of hIAPP-membrane interaction, including the adsorption orientation and conformation of hIAPP monomer at an anionic POPG lipid bilayer by performing all-atom molecular dynamics simulations. We found that hIAPP monomer is quickly adsorbed to bilayer surface, and the adsorption is initiated from the N-terminal residues driven by strong electrostatic interactions of the positively-charged residues K1 and R11 with negatively-charged lipid headgroups. hIAPP binds parallel to the lipid bilayer surface as a stable helix through residues 7–22, consistent with previous experimental study. Remarkably, different simulations lead to the same binding orientation stabilized by electrostatic and H-bonding interactions, with residues R11, F15 and S19 oriented towards membrane and hydrophobic residues L12, A13, L16 and V17 exposed to solvent. Implications for membrane-mediated hIAPP aggregation are discussed.

Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling

International Nuclear Information System (INIS)

Pera, H.; Kleijn, J. M.; Leermakers, F. A. M.

2014-01-01

To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus k c and k ¯ and the preferred monolayer curvature J 0 m , and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of k c and the area compression modulus k A are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for k ¯ and J 0 m can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both k ¯ and J 0 m change sign with relevant parameter changes. Although typically k ¯ 0 m ≫0, especially at low ionic strengths. We anticipate that these changes lead to unstable membranes as these become vulnerable to pore formation or disintegration into lipid disks

SH2 Domains Serve as Lipid-Binding Modules for pTyr-Signaling Proteins.

Science.gov (United States)

Park, Mi-Jeong; Sheng, Ren; Silkov, Antonina; Jung, Da-Jung; Wang, Zhi-Gang; Xin, Yao; Kim, Hyunjin; Thiagarajan-Rosenkranz, Pallavi; Song, Seohyeon; Yoon, Youngdae; Nam, Wonhee; Kim, Ilshin; Kim, Eui; Lee, Dong-Gyu; Chen, Yong; Singaram, Indira; Wang, Li; Jang, Myoung Ho; Hwang, Cheol-Sang; Honig, Barry; Ryu, Sungho; Lorieau, Justin; Kim, You-Me; Cho, Wonhwa

2016-04-07

The Src-homology 2 (SH2) domain is a protein interaction domain that directs myriad phosphotyrosine (pY)-signaling pathways. Genome-wide screening of human SH2 domains reveals that ∼90% of SH2 domains bind plasma membrane lipids and many have high phosphoinositide specificity. They bind lipids using surface cationic patches separate from pY-binding pockets, thus binding lipids and the pY motif independently. The patches form grooves for specific lipid headgroup recognition or flat surfaces for non-specific membrane binding and both types of interaction are important for cellular function and regulation of SH2 domain-containing proteins. Cellular studies with ZAP70 showed that multiple lipids bind its C-terminal SH2 domain in a spatiotemporally specific manner and thereby exert exquisite spatiotemporal control over its protein binding and signaling activities in T cells. Collectively, this study reveals how lipids control SH2 domain-mediated cellular protein-protein interaction networks and suggest a new strategy for therapeutic modulation of pY-signaling pathways. Copyright © 2016 Elsevier Inc. All rights reserved.

A new look at lipid-membrane structure in relation to drug research

DEFF Research Database (Denmark)

Mouritsen, Ole G.; Jørgensen, Kent

1998-01-01

Lipid-bilayer membranes are key objects in drug research in relation to (i) interaction of drugs with membrane-bound receptors, (ii) drug targeting, penetration, and permeation of cell membranes, and (iii) use of liposomes in micro-encapsulation technologies for drug delivery. Rational design...... of new drugs and drug-delivery systems therefore requries insight into the physical properties of lipid-bilayer membranes. This mini-review provides a perspective on the current view of lipid-bilayer structure and dynamics based on information obtained from a variety of recent experimental...... and theoretical studies. Special attention is paid to trans-bilayer structure, lateral molecular organization of the lipid bilayer, lipid-mediated protein assembly, and lipid-bilayer permeability. It is argued that lipids play a major role in lipid membrane-organization and functionality....

Single channel planar lipid bilayer recordings of the melittin variant MelP5.

Science.gov (United States)

Fennouri, Aziz; Mayer, Simon Finn; Schroeder, Thomas B H; Mayer, Michael

2017-10-01

MelP5 is a 26 amino acid peptide derived from melittin, the main active constituent of bee venom, with five amino acid replacements. The pore-forming activity of MelP5 in lipid membranes is attracting attention because MelP5 forms larger pores and induces dye leakage through liposome membranes at a lower concentration than melittin. Studies of MelP5 have so far focused on ensemble measurements of membrane leakage and impedance; here we extend this characterization with an electrophysiological comparison between MelP5 and melittin using planar lipid bilayer recordings. These experiments reveal that MelP5 pores in lipid membranes composed of 3:1 phosphatidylcholine:cholesterol consist of an average of 10 to 12 monomers compared to an average of 3 to 9 monomers for melittin. Both peptides form transient pores with dynamically varying conductance values similar to previous findings for melittin, but MelP5 occasionally also forms stable, well-defined pores with single channel conductance values that vary greatly and range from 50 to 3000pS in an electrolyte solution containing 100mM KCl. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Nanobioarchitectures based on chlorophyll photopigment, artificial lipid bilayers and carbon nanotubes

Directory of Open Access Journals (Sweden)

Marcela Elisabeta Barbinta-Patrascu

2014-12-01

Full Text Available In the last decade, building biohybrid materials has gained considerable interest in the field of nanotechnology. This paper describes an original design for bionanoarchitectures with interesting properties and potential bioapplications. Multilamellar lipid vesicles (obtained by hydration of a dipalmitoyl phosphatidylcholine thin film with and without cholesterol were labelled with a natural photopigment (chlorophyll a, which functioned as a sensor to detect modifications in the artificial lipid bilayers. These biomimetic membranes were used to build non-covalent structures with single-walled carbon nanotubes. Different biophysical methods were employed to characterize these biohybrids such as: UV–vis absorption and emission spectroscopy, zeta potential measurements, AFM and chemiluminescence techniques. The designed, carbon-based biohybrids exhibited good physical stability, good antioxidant and antimicrobial properties, and could be used as biocoating materials. As compared to the cholesterol-free samples, the cholesterol-containing hybrid structures demonstrated better stability (i.e., their zeta potential reached the value of −36.4 mV, more pronounced oxygen radical scavenging ability (affording an antioxidant activity of 73.25% and enhanced biocidal ability, offering inhibition zones of 12.4, 11.3 and 10.2 mm in diameter, against Escherichia coli, Staphylococcus aureus and Enterococcus faecalis, respectively.

Structural interactions between lipids, water and S1-S4 voltage-sensing domains.

Science.gov (United States)

Krepkiy, Dmitriy; Gawrisch, Klaus; Swartz, Kenton J

2012-11-02

Membrane proteins serve crucial signaling and transport functions, yet relatively little is known about their structures in membrane environments or how lipids interact with these proteins. For voltage-activated ion channels, X-ray structures suggest that the mobile voltage-sensing S4 helix would be exposed to the membrane, and functional studies reveal that lipid modification can profoundly alter channel activity. Here, we use solid-state NMR to investigate structural interactions of lipids and water with S1-S4 voltage-sensing domains and to explore whether lipids influence the structure of the protein. Our results demonstrate that S1-S4 domains exhibit extensive interactions with lipids and that these domains are heavily hydrated when embedded in a membrane. We also find evidence for preferential interactions of anionic lipids with S1-S4 domains and that these interactions have lifetimes on the timescale of ≤ 10(-3)s. Arg residues within S1-S4 domains are well hydrated and are positioned in close proximity to lipids, exhibiting local interactions with both lipid headgroups and acyl chains. Comparative studies with a positively charged lipid lacking a phosphodiester group reveal that this lipid modification has only modest effects on the structure and hydration of S1-S4 domains. Taken together, our results demonstrate that Arg residues in S1-S4 voltage-sensing domains reside in close proximity to the hydrophobic interior of the membrane yet are well hydrated, a requirement for carrying charge and driving protein motions in response to changes in membrane voltage. Published by Elsevier Ltd.

Plant lipid environment and membrane enzymes: the case of the plasma membrane H+-ATPase.

Science.gov (United States)

Morales-Cedillo, Francisco; González-Solís, Ariadna; Gutiérrez-Angoa, Lizbeth; Cano-Ramírez, Dora Luz; Gavilanes-Ruiz, Marina

2015-04-01

Several lipid classes constitute the universal matrix of the biological membranes. With their amphipathic nature, lipids not only build the continuous barrier that confers identity to every cell and organelle, but they are also active actors that modulate the activity of the proteins immersed in the lipid bilayer. The plasma membrane H(+)-ATPase, an enzyme from plant cells, is an excellent example of a transmembrane protein whose activity is influenced by the hydrophilic compartments at both sides of the membrane and by the hydrophobic domains of the lipid bilayer. As a result, an extensive documentation of the effect of numerous amphiphiles in the enzyme activity can be found. Detergents, membrane glycerolipids, and sterols can produce activation or inhibition of the enzyme activity. In some cases, these effects are associated with the lipids of the membrane bulk, but in others, a direct interaction of the lipid with the protein is involved. This review gives an account of reports related to the action of the membrane lipids on the H(+)-ATPase activity.

Lipid nanoparticle interactions and assemblies

Science.gov (United States)

Preiss, Matthew Ryan

Novel liposome-nanoparticle assemblies (LNAs) provide a biologically inspired route for designing multifunctional bionanotheranostics. LNAs combine the benefits of lipids and liposomes to encapsulate, transport, and protect hydrophilic and hydrophobic therapeutics with functional nanoparticles. Functional nanoparticles endow LNAs with additional capabilities, including the ability to target diseases, triggered drug release, controlled therapeutic output, and diagnostic capabilities to produce a drug delivery system that can effectively and efficiently deliver therapeutics while reducing side effects. Not only could LNAs make existing drugs better, they could also provide an avenue to allow once promising non-approved drugs (rejected due to harmful side effects, inadequate pharmacokinetics, and poor efficacy) to be safely used through targeted and controlled delivery directly to the diseased site. LNAs have the potential to be stimuli responsive, delivering drugs on command by external (ultrasound, RF heating, etc.) or internal (pH, blood sugar, heart rate, etc.) stimuli. Individually, lipids and nanoparticles have been clinically approved for therapy, such as Doxil (a liposomal doxorubicin for cancer treatment), and diagnosis, such as Feridex (an iron oxide nanoparticle an MRI contrast enhancement agent for liver tumors). In order to engineer these multifunctional LNAs for theranostic applications, the interactions between nanoparticles and lipids must be better understood. This research sought to explore the formation, design, structures, characteristics, and functions of LNAs. To achieve this goal, different types of LNAs were formed, specifically magnetoliposomes, bilayer decorated LNAs (DLNAs), and lipid-coated magnetic nanoparticles (LMNPs). A fluorescent probe was embedded in the lipid bilayer of magnetoliposomes allowing the local temperature and membrane fluidity to be observed. When subjected to an electromagnetic field that heated the encapsulated iron

Lipid bilayer membranes: Missing link in the comprehension of synovial lubrication?

Science.gov (United States)

Packard, Ross; Cowley, Leonie; Dubief, Yves

2010-03-01

The human body hosts an extremely efficient tribological system in its synovial joints that operate under very low friction and virtually no wear. It has long been assumed that the higher molecular weight molecules present in the synovial fluid (hyaluronic acid, lubricin) are solely responsible for the mechanical properties of joint. Smaller components, unsaturated phospholipids, have a virtually an undefined role, most probably because of the cancellation of their amphiphilic properties ex vivo caused by oxidation. Using experimental observations of multilamellar arrangements in synovial joints, we formulate the assumption that self-assembling structures provide the anisotropy necessary to synovial fluid to resist drainage under normal compression. Our molecular dynamics simulations demonstrate the tremendous mechanical properties of lipid bilayers and also highlight their weakening consistent with modifications resulting from injuries or joint prosthesis.

Multiscale Simulations Suggest a Mechanism for the Association of the Dok7 PH Domain with PIP-Containing Membranes.

Directory of Open Access Journals (Sweden)

Amanda Buyan

2016-07-01

Full Text Available Dok7 is a peripheral membrane protein that is associated with the MuSK receptor tyrosine kinase. Formation of the Dok7/MuSK/membrane complex is required for the activation of MuSK. This is a key step in the complex exchange of signals between neuron and muscle, which lead to neuromuscular junction formation, dysfunction of which is associated with congenital myasthenic syndromes. The Dok7 structure consists of a Pleckstrin Homology (PH domain and a Phosphotyrosine Binding (PTB domain. The mechanism of the Dok7 association with the membrane remains largely unknown. Using multi-scale molecular dynamics simulations we have explored the formation of the Dok7 PH/membrane complex. Our simulations indicate that the PH domain of Dok7 associates with membranes containing phosphatidylinositol phosphates (PIPs via interactions of the β1/β2, β3/β4, and β5/β6 loops, which together form a positively charged surface on the PH domain and interact with the negatively charged headgroups of PIP molecules. The initial encounter of the Dok7 PH domain is followed by formation of additional interactions with the lipid bilayer, and especially with PIP molecules, which stabilizes the Dok7 PH/membrane complex. We have quantified the binding of the PH domain to the model bilayers by calculating a density landscape for protein/membrane interactions. Detailed analysis of the PH/PIP interactions reveal both a canonical and an atypical site to be occupied by the anionic lipid. PH domain binding leads to local clustering of PIP molecules in the bilayer. Association of the Dok7 PH domain with PIP lipids is therefore seen as a key step in localization of Dok7 to the membrane and formation of a complex with MuSK.

Neutron scattering to study membrane systems: from lipid vesicles to living cells.

Energy Technology Data Exchange (ETDEWEB)

Nickels, Jonathan D. [ORNL; Chatterjee, Sneha [ORNL; Stanley, Christopher B. [ORNL; Qian, Shuo [ORNL; Cheng, Xiaolin [ORNL; Myles, Dean A A [ORNL; Standaert, Robert F. [ORNL; Elkins, James G. [ORNL; Katsaras, John [ORNL

2017-03-01

The existence and role of lateral lipid organization in biological membranes has been studied and contested for more than 30 years. Lipid domains, or rafts, are hypothesized as scalable compartments in biological membranes, providing appropriate physical environments to their resident membrane proteins. This implies that lateral lipid organization is associated with a range of biological functions, such as protein co-localization, membrane trafficking, and cell signaling, to name just a few. Neutron scattering techniques have proven to be an excellent tool to investigate these structural features in model lipids, and more recently, in living cells. I will discuss our recent work using neutrons to probe the structure and mechanical properties in model lipid systems and our current efforts in using neutrons to probe the structure and organization of the bilayer in a living cell. These efforts in living cells have used genetic and biochemical strategies to generate a large neutron scattering contrast, making the membrane visible. I will present our results showing in vivo bilayer structure and discuss the outlook for this approach.

Reversible tuning of the wettability on a silver mesodendritic surface by the formation and disruption of lipid-like bilayers

Science.gov (United States)

Gao, Yuanji; Xia, Bing; Liu, Jie; Ding, Lisheng; Li, Bangjing; Zhou, Yan

2015-02-01

This study reported a smart, easy to apply, flexible and green strategy for obtaining a biomimic micro-nanostructures. 1-Mercapto-12-(p-nitrophenoxy) dodecane (MPND) and n-dodecanethiol were used to form low surface energy film on a silver mesodendritic structure coated zinc substrate. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize surface morphology and mesocrystal structures. Noncovalently linked sodium nonanoyloxy benzene sulfonate (NOBS) was used to form "lipid-like bilayers" on the surface, making it possible for the surface to switch its surface wettability reversibly. The water contact angle (CA) on the constructed surface varies from 168 ± 2° (before processed by NOBS) to 55 ± 2° (after processed by NOBS). This phenomenon can be explained by the formation and disruption of "lipid-like bilayers" to affect the wettability of the surface. This work is of great scientific interests and may provide insights into the design of novel functional devices that are relevant to surface wettability, such as microfluidic devices and sensors.

Proton and carbon-13 nuclear magnetic resonance studies of the effects of retinal on the dynamic structure and stability of lipid bilayer

International Nuclear Information System (INIS)

Inoue, Yoshio; Hanafusa, Yoshito; Toda, Masakazu; Chujo, Riichiro

1982-01-01

The effects of retinal and vitamin A on the dynamic structure and stability of hen egg yolk lecithin bilayers have been studied by means of carbon-13 and proton NMR spectroscopies. 13 C spin-lattice relaxation and paramagnetic ion permeability studies on lecithin bilayers indicate a marked decrease in flexibility of the lipid acyl chain and a breakdown of membrane impermeableness to ion by the intercalated all-trans- and 11-cis-retinal, whereas the effect of incorporated vitamin A on the fluidity of bilayers is small and its impermeableness to ion remains effective even in the presence of higher concentration of vitamin A. The experimental results are discussed in connection with the mechanism of the permeability change in photoreceptive disk membrane. (author)

Lipid Configurations from Molecular Dynamics Simulations

DEFF Research Database (Denmark)

Pezeshkian, Weria; Khandelia, Himanshu; Marsh, Derek

2018-01-01

of dihedral angles in palmitoyl-oleoyl phosphatidylcholine from molecular dynamics simulations of hydrated fluid bilayer membranes. We compare results from the widely used lipid force field of Berger et al. with those from the most recent C36 release of the CHARMM force field for lipids. Only the CHARMM force......The extent to which current force fields faithfully reproduce conformational properties of lipids in bilayer membranes, and whether these reflect the structural principles established for phospholipids in bilayer crystals, are central to biomembrane simulations. We determine the distribution...

Exploring the raft-hypothesis by probing planar bilayer patches of free-standing giant vesicles at nanoscale resolution, with and without Na,K-ATPase

DEFF Research Database (Denmark)

Bhartia, Tripta; Cornelius, Flemming; Ipsen, J. H.

2016-01-01

The structure of functional lipid domains (rafts) in biological membranes has for long time been unresolved due to their small length scales and transient nature. These cooperative properties of the lipid bilayer matrix are modelled by free-standing giant unilammellar vesicles (GUVs) with well...... mixtures of DOPC/DPPC/cholesterol with and without Na,K-ATPase (NKA), a transmembrane protein known to be associated with rafts. Two mechanisms of domain formation are revealed: 1) close to lo/ld phase coexistence, domains in size up to 100 nm appear as thermally induced droplet fluctuations, 2) NKA shows...... interfacial activity and cluster in lo/ld micro-emulsion droplets. Some perspectives for the application of the techniques and the understanding of the nature of raft domains are outlined....

PEGylated Lipid bilayer coated mesoporous silica nanoparticles for co-delivery of paclitaxel and curcumin: Design, characterization and its cytotoxic effect.

Science.gov (United States)

Lin, Jiahao; Cai, Qiang; Tang, Yinian; Xu, Yanjun; Wang, Qian; Li, Tingting; Xu, Huihao; Wang, Shuaiyu; Fan, Kai; Liu, Zhongjie; Jin, Yipeng; Lin, Degui

2018-01-30

Highly ordered mesoporous silica nanoparticles (MSNs) with pore diameter of 2.754nm and particle size of 115±15nm were prepared with etching method. Homogeneous PEGylated lipid bilayer with 10-15nm thickness was coated around the surface of MSNs using film hydration method. Systematic optimization and characterization of co-encapsulation process of paclitaxel (Tax) and curcumin (Cur) into PEGylated lipid bilayer coated mesoporous silica nanoparticles (PLMSNs) were performed carrying out single factor test, associated with Box-Behnken Design. The concentration of encapsulated drugs was measured by reversed phase high performance liquid chromatography (RP-HPLC) method. Optimal factor settings were as follows: 50mg MSNs, ratio of MSNs to lipid (w/w)=1:1.11, and ratio of lipid to CHO (w/w)=3.93:1. The average experimental EE Tax , EE Cur and stability score value were (77.48±2.73) %, (30.70±3.56) % and 4 point respectively based on the conditions mentioned above. Morphology determination of Tax-Cur-PLMSNs revealed that the composite nanoparticles were spherical particals with uniform dispersion. In vitro release experiment indicated that PLMSNs improved dissolution of Tax compared to Tax powder suspension and exhibited sustained release property. Tax-Cur-PLMSNs manifested definite and persistently promoted cytotoxic effect against canine breast cancer cells. This prolonged and enhanced activity of Tax-Cur-PLMSNs might contribute to its sustained release effect. Copyright © 2017. Published by Elsevier B.V.

Molecular dynamics study of lipid bilayers modeling the plasma membranes of mouse hepatocytes and hepatomas.

Science.gov (United States)

Andoh, Yoshimichi; Aoki, Noriyuki; Okazaki, Susumu

2016-02-28

Molecular dynamics (MD) calculations of lipid bilayers modeling the plasma membranes of normal mouse hepatocytes and hepatomas in water have been performed under physiological isothermal-isobaric conditions (310.15 K and 1 atm). The changes in the membrane properties induced by hepatic canceration were investigated and were compared with previous MD calculations included in our previous study of the changes in membrane properties induced by murine thymic canceration. The calculated model membranes for normal hepatocytes and hepatomas comprised 23 and 24 kinds of lipids, respectively. These included phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophospholipids, and cholesterol. We referred to previously published experimental values for the mole fraction of the lipids adopted in the present calculations. The calculated structural and dynamic properties of the membranes such as lateral structure, order parameters, lateral self-diffusion constants, and rotational correlation times all showed that hepatic canceration causes plasma membranes to become more ordered laterally and less fluid. Interestingly, this finding contrasts with the less ordered structure and increased fluidity of plasma membranes induced by thymic canceration observed in our previous MD study.

Antimicrobial peptides at work: interaction of myxinidin and its mutant WMR with lipid bilayers mimicking the P. aeruginosa and E. coli membranes

Science.gov (United States)

Lombardi, Lucia; Stellato, Marco Ignazio; Oliva, Rosario; Falanga, Annarita; Galdiero, Massimiliano; Petraccone, Luigi; D'Errico, Geradino; de Santis, Augusta; Galdiero, Stefania; Del Vecchio, Pompea

2017-03-01

Antimicrobial peptides are promising candidates as future therapeutics in order to face the problem of antibiotic resistance caused by pathogenic bacteria. Myxinidin is a peptide derived from the hagfish mucus displaying activity against a broad range of bacteria. We have focused our studies on the physico-chemical characterization of the interaction of myxinidin and its mutant WMR, which contains a tryptophan residue at the N-terminus and four additional positive charges, with two model biological membranes (DOPE/DOPG 80/20 and DOPE/DOPG/CL 65/23/12), mimicking respectively Escherichia coli and Pseudomonas aeruginosa membrane bilayers. All our results have coherently shown that, although both myxinidin and WMR interact with the two membranes, their effect on membrane microstructure and stability are different. We further have shown that the presence of cardiolipin plays a key role in the WMR-membrane interaction. Particularly, WMR drastically perturbs the DOPE/DOPG/CL membrane stability inducing a segregation of anionic lipids. On the contrary, myxinidin is not able to significantly perturb the DOPE/DOPG/CL bilayer whereas interacts better with the DOPE/DOPG bilayer causing a significant perturbing effect of the lipid acyl chains. These findings are fully consistent with the reported greater antimicrobial activity of WMR against P. aeruginosa compared with myxinidin.

Electron density analysis of the effects of sugars on the structure of lipid bilayers at low hydration - a preliminary study

Energy Technology Data Exchange (ETDEWEB)

Lenné, T.; Kent, B.; Koster, K.L.; Garvey, C.J.; Bryant, G. (ANSTO); (USD); (ANU); (RMIT)

2012-02-06

Small angle X-ray scattering is used to study the effects of sugars on membranes during dehydration. Previous work has shown that the bilayer and chain-chain repeat spacings of DPPC bilayers are relatively unaffected by the presence of sugars. In this work we present a preliminary analysis of the electron density profiles of DPPC in the presence of sugars at low hydration. The difficulties of determining the correct phasing are discussed. Sugars and other small solutes have been shown to have an important role in improving the tolerance of a range of species to desiccation and freezing. In particular it has been shown that sugars can stabilize membranes in the fluid membrane phase during dehydration, and in the fully dehydrated state. Equivalently, at a particular hydration, the presence of sugars lowers the transition temperature between the fluid and gel phases. There are two competing models for explaining the effects of sugars on membrane phase transition temperatures. One, designated the water replacement hypothesis (WRH) states that sugars hydrogen bond to phospholipid headgroups, thus hindering the fluid-gel phase transition. One version of this model suggests that certain sugars (such as trehalose) achieve the measured effects by inserting between the phospholipid head groups. An alternative model explains the observed effects of sugars in terms of the sugars effect on the hydration repulsion that develops between opposing membranes during dehydration. The hydration repulsion leads to a lateral compressive stress in the bilayer which squeezes adjacent lipids more closely together, resulting in a transition to the gel phase. When sugars are present, their osmotic and volumetric effects reduce the hydration repulsion, reduce the compressive stress in the membranes, and therefore tend to maintain the average lateral separation between lipids. This model is called the hydration forces explanation (HFE). We recently showed that neither mono- nor di

TrackArt: the user friendly interface for single molecule tracking data analysis and simulation applied to complex diffusion in mica supported lipid bilayers.

Science.gov (United States)

Matysik, Artur; Kraut, Rachel S

2014-05-01

Single molecule tracking (SMT) analysis of fluorescently tagged lipid and protein probes is an attractive alternative to ensemble averaged methods such as fluorescence correlation spectroscopy (FCS) or fluorescence recovery after photobleaching (FRAP) for measuring diffusion in artificial and plasma membranes. The meaningful estimation of diffusion coefficients and their errors is however not straightforward, and is heavily dependent on sample type, acquisition method, and equipment used. Many approaches require advanced computing and programming skills for their implementation. Here we present TrackArt software, an accessible graphic interface for simulation and complex analysis of multiple particle paths. Imported trajectories can be filtered to eliminate spurious or corrupted tracks, and are then analyzed using several previously described methodologies, to yield single or multiple diffusion coefficients, their population fractions, and estimated errors. We use TrackArt to analyze the single-molecule diffusion behavior of a sphingolipid analog SM-Atto647N, in mica supported DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) bilayers. Fitting with a two-component diffusion model confirms the existence of two separate populations of diffusing particles in these bilayers on mica. As a demonstration of the TrackArt workflow, we characterize and discuss the effective activation energies required to increase the diffusion rates of these populations, obtained from Arrhenius plots of temperature-dependent diffusion. Finally, TrackArt provides a simulation module, allowing the user to generate models with multiple particle trajectories, diffusing with different characteristics. Maps of domains, acting as impermeable or permeable obstacles for particles diffusing with given rate constants and diffusion coefficients, can be simulated or imported from an image. Importantly, this allows one to use simulated data with a known diffusion behavior as a comparison for results

Communication: Orientational self-ordering of spin-labeled cholesterol analogs in lipid bilayers in diluted conditions

Energy Technology Data Exchange (ETDEWEB)

Kardash, Maria E.; Dzuba, Sergei A., E-mail: dzuba@kinetics.nsc.ru [Voevodsky Institute of Chemical Kinetics and Combustion, 630090 Novosibirsk, Russia, and Novosibirsk State University, 630090 Novosibirsk (Russian Federation)

2014-12-07

Lipid-cholesterol interactions are responsible for different properties of biological membranes including those determining formation in the membrane of spatial inhomogeneities (lipid rafts). To get new information on these interactions, electron spin echo (ESE) spectroscopy, which is a pulsed version of electron paramagnetic resonance (EPR), was applied to study 3β-doxyl-5α-cholestane (DCh), a spin-labeled analog of cholesterol, in phospholipid bilayer consisted of equimolecular mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phosphocholine. DCh concentration in the bilayer was between 0.1 mol.% and 4 mol.%. For comparison, a reference system containing a spin-labeled 5-doxyl-stearic acid (5-DSA) instead of DCh was studied as well. The effects of “instantaneous diffusion” in ESE decay and in echo-detected (ED) EPR spectra were explored for both systems. The reference system showed good agreement with the theoretical prediction for the model of spin labels of randomly distributed orientations, but the DCh system demonstrated remarkably smaller effects. The results were explained by assuming that neighboring DCh molecules are oriented in a correlative way. However, this correlation does not imply the formation of clusters of cholesterol molecules, because conventional continuous wave EPR spectra did not show the typical broadening due to aggregation of spin labels and the observed ESE decay was not faster than in the reference system. So the obtained data evidence that cholesterol molecules at low concentrations in biological membranes can interact via large distances of several nanometers which results in their orientational self-ordering.

New cytotoxic butyltin complexes with 2-sulfobenzoic acid: Molecular interaction with lipid bilayers and DNA as well as in vitro anticancer activity

Czech Academy of Sciences Publication Activity Database

Pruchnik, H.; Kral, Teresa; Poradowski, D.; Drynda, A.; Obmińska-Mrukowicz, B.; Hof, Martin

2016-01-01

Roč. 243, JAN 2016 (2016), s. 107-118 ISSN 0009-2797 R&D Projects: GA ČR GBP208/12/G016 Institutional support: RVO:61388955 Keywords : Butyltin 2-sulfobenzoates * Antitumor activity * Lipid bilayer Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.143, year: 2016

Effect of the aminoacid composition of model α-helical peptides on the physical properties of lipid bilayers and peptide conformation: a molecular dynamics simulation

Czech Academy of Sciences Publication Activity Database

Melicherčík, Milan; Holúbeková, A.; Hianik, T.; Urban, J.

2013-01-01

Roč. 19, č. 11 (2013), s. 4723-4730 ISSN 1610-2940 Institutional support: RVO:67179843 Keywords : Bilayer lipid membranes * Helical peptides * Molecular dynamics simulations * Phase transitions Subject RIV: BO - Biophysics Impact factor: 1.867, year: 2013

Surface coating of siRNA-peptidomimetic nano-self-assemblies with anionic lipid bilayers: enhanced gene silencing and reduced adverse effects in vitro

Science.gov (United States)

Zeng, Xianghui; de Groot, Anne Marit; Sijts, Alice J. A. M.; Broere, Femke; Oude Blenke, Erik; Colombo, Stefano; van Eden, Willem; Franzyk, Henrik; Nielsen, Hanne Mørck; Foged, Camilla

2015-11-01

Cationic vectors have demonstrated the potential to facilitate intracellular delivery of therapeutic oligonucleotides. However, enhanced transfection efficiency is usually associated with adverse effects, which also proves to be a challenge for vectors based on cationic peptides. In this study a series of proteolytically stable palmitoylated α-peptide/β-peptoid peptidomimetics with a systematically varied number of repeating lysine and homoarginine residues was shown to self-assemble with small interfering RNA (siRNA). The resulting well-defined nanocomplexes were coated with anionic lipids giving rise to net anionic liposomes. These complexes and the corresponding liposomes were optimized towards efficient gene silencing and low adverse effects. The optimal anionic liposomes mediated a high silencing effect, which was comparable to that of the control (cationic Lipofectamine 2000), and did not display any noticeable cytotoxicity and immunogenicity in vitro. In contrast, the corresponding nanocomplexes mediated a reduced silencing effect with a more narrow safety window. The surface coating with anionic lipid bilayers led to partial decomplexation of the siRNA-peptidomimetic nanocomplex core of the liposomes, which facilitated siRNA release. Additionally, the optimal anionic liposomes showed efficient intracellular uptake and endosomal escape. Therefore, these findings suggest that a more efficacious and safe formulation can be achieved by surface coating of the siRNA-peptidomimetic nano-self-assemblies with anionic lipid bilayers.Cationic vectors have demonstrated the potential to facilitate intracellular delivery of therapeutic oligonucleotides. However, enhanced transfection efficiency is usually associated with adverse effects, which also proves to be a challenge for vectors based on cationic peptides. In this study a series of proteolytically stable palmitoylated α-peptide/β-peptoid peptidomimetics with a systematically varied number of repeating lysine

Diffusion and spectroscopy of water and lipids in fully hydrated dimyristoylphosphatidylcholine bilayer membranes

International Nuclear Information System (INIS)

Yang, J.; Martí, J.; Calero, C.

2014-01-01

Microscopic structure and dynamics of water and lipids in a fully hydrated dimyristoylphosphatidylcholine phospholipid lipid bilayer membrane in the liquid-crystalline phase have been analyzed with all-atom molecular dynamics simulations based on the recently parameterized CHARMM36 force field. The diffusive dynamics of the membrane lipids and of its hydration water, their reorientational motions as well as their corresponding spectral densities, related to the absorption of radiation, have been considered for the first time using the present force field. In addition, structural properties such as density and pressure profiles, a deuterium-order parameter, surface tension, and the extent of water penetration in the membrane have been analyzed. Molecular self-diffusion, reorientational motions, and spectral densities of atomic species reveal a variety of time scales playing a role in membrane dynamics. The mechanisms of lipid motion strongly depend on the time scale considered, from fast ballistic translation at the scale of picoseconds (effective diffusion coefficients of the order of 10 −5 cm 2 /s) to diffusive flow of a few lipids forming nanodomains at the scale of hundreds of nanoseconds (diffusion coefficients of the order of 10 −8 cm 2 /s). In the intermediate regime of sub-diffusion, collisions with nearest neighbors prevent the lipids to achieve full diffusion. Lipid reorientations along selected directions agree well with reported nuclear magnetic resonance data and indicate two different time scales, one about 1 ns and a second one in the range of 2–8 ns. We associated the two time scales of reorientational motions with angular distributions of selected vectors. Calculated spectral densities corresponding to lipid and water reveal an overall good qualitative agreement with Fourier transform infrared spectroscopy experiments. Our simulations indicate a blue-shift of the low frequency spectral bands of hydration water as a result of its interaction

Diffusion and spectroscopy of water and lipids in fully hydrated dimyristoylphosphatidylcholine bilayer membranes

Energy Technology Data Exchange (ETDEWEB)

Yang, J.; Martí, J., E-mail: jordi.marti@upc.edu [Department of Physics and Nuclear Engineering, Technical University of Catalonia-Barcelona Tech, B4-B5 Northern Campus, Jordi Girona 1-3, 08034 Barcelona, Catalonia (Spain); Calero, C. [Department of Physics and Nuclear Engineering, Technical University of Catalonia-Barcelona Tech, B4-B5 Northern Campus, Jordi Girona 1-3, 08034 Barcelona, Catalonia (Spain); Center for Polymer Studies, Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215 (United States)

2014-03-14

Microscopic structure and dynamics of water and lipids in a fully hydrated dimyristoylphosphatidylcholine phospholipid lipid bilayer membrane in the liquid-crystalline phase have been analyzed with all-atom molecular dynamics simulations based on the recently parameterized CHARMM36 force field. The diffusive dynamics of the membrane lipids and of its hydration water, their reorientational motions as well as their corresponding spectral densities, related to the absorption of radiation, have been considered for the first time using the present force field. In addition, structural properties such as density and pressure profiles, a deuterium-order parameter, surface tension, and the extent of water penetration in the membrane have been analyzed. Molecular self-diffusion, reorientational motions, and spectral densities of atomic species reveal a variety of time scales playing a role in membrane dynamics. The mechanisms of lipid motion strongly depend on the time scale considered, from fast ballistic translation at the scale of picoseconds (effective diffusion coefficients of the order of 10{sup −5} cm{sup 2}/s) to diffusive flow of a few lipids forming nanodomains at the scale of hundreds of nanoseconds (diffusion coefficients of the order of 10{sup −8} cm{sup 2}/s). In the intermediate regime of sub-diffusion, collisions with nearest neighbors prevent the lipids to achieve full diffusion. Lipid reorientations along selected directions agree well with reported nuclear magnetic resonance data and indicate two different time scales, one about 1 ns and a second one in the range of 2–8 ns. We associated the two time scales of reorientational motions with angular distributions of selected vectors. Calculated spectral densities corresponding to lipid and water reveal an overall good qualitative agreement with Fourier transform infrared spectroscopy experiments. Our simulations indicate a blue-shift of the low frequency spectral bands of hydration water as a result of

Poisson-Boltzmann versus Size-Modified Poisson-Boltzmann Electrostatics Applied to Lipid Bilayers.

Science.gov (United States)

Wang, Nuo; Zhou, Shenggao; Kekenes-Huskey, Peter M; Li, Bo; McCammon, J Andrew

2014-12-26

Mean-field methods, such as the Poisson-Boltzmann equation (PBE), are often used to calculate the electrostatic properties of molecular systems. In the past two decades, an enhancement of the PBE, the size-modified Poisson-Boltzmann equation (SMPBE), has been reported. Here, the PBE and the SMPBE are reevaluated for realistic molecular systems, namely, lipid bilayers, under eight different sets of input parameters. The SMPBE appears to reproduce the molecular dynamics simulation results better than the PBE only under specific parameter sets, but in general, it performs no better than the Stern layer correction of the PBE. These results emphasize the need for careful discussions of the accuracy of mean-field calculations on realistic systems with respect to the choice of parameters and call for reconsideration of the cost-efficiency and the significance of the current SMPBE formulation.

Using crosslinkable diacetylene phospholipids to construct two-dimensional packed beds in supported lipid bilayer separation platforms

Directory of Open Access Journals (Sweden)

Shu-Kai Hu, Sheng-Wen Hsiao, Hsun-Yen Mao, Ya-Ming Chen, Yung Chang and Ling Chao

2013-01-01

Full Text Available Separating and purifying cell membrane-associated biomolecules has been a challenge owing to their amphiphilic property. Taking these species out of their native lipid membrane environment usually results in biomolecule degradation. One of the new directions is to use supported lipid bilayer (SLB platforms to separate the membrane species while they are protected in their native environment. Here we used a type of crosslinkable diacetylene phospholipids, diynePC (1,2-bis(10,12-tricosadiynoyl-sn-glycero-3-phosphocholine, as a packed material to create a 'two-dimensional (2D packed bed' in a SLB platform. After the diynePC SLB is exposed to UV light, some of the diynePC lipids in the SLB can crosslink and the non-crosslinked monomer lipids can be washed away, leaving a 2D porous solid matrix. We incorporated the lipid vesicle deposition method with a microfluidic device to pattern the location of the packed-bed region and the feed region with species to be separated in a SLB platform. Our atomic force microscopy result shows that the nano-scaled structure density of the '2D packed bed' can be tuned by the UV dose applied to the diynePC membrane. When the model membrane biomolecules were forced to transport through the packed-bed region, their concentration front velocities were found to decrease linearly with the UV dose, indicating the successful creation of packed obstacles in these 2D lipid membrane separation platforms.

Phosphatidylserine Lateral Organization Influences the Interaction of Influenza Virus Matrix Protein 1 with Lipid Membranes.

Science.gov (United States)

Bobone, Sara; Hilsch, Malte; Storm, Julian; Dunsing, Valentin; Herrmann, Andreas; Chiantia, Salvatore

2017-06-15

Influenza A virus matrix protein 1 (M1) is an essential component involved in the structural stability of the virus and in the budding of new virions from infected cells. A deeper understanding of the molecular basis of virion formation and the budding process is required in order to devise new therapeutic approaches. We performed a detailed investigation of the interaction between M1 and phosphatidylserine (PS) (i.e., its main binding target at the plasma membrane [PM]), as well as the distribution of PS itself, both in model membranes and in living cells. To this end, we used a combination of techniques, including Förster resonance energy transfer (FRET), confocal microscopy imaging, raster image correlation spectroscopy, and number and brightness (N&B) analysis. Our results show that PS can cluster in segregated regions in the plane of the lipid bilayer, both in model bilayers constituted of PS and phosphatidylcholine and in living cells. The viral protein M1 interacts specifically with PS-enriched domains, and such interaction in turn affects its oligomerization process. Furthermore, M1 can stabilize PS domains, as observed in model membranes. For living cells, the presence of PS clusters is suggested by N&B experiments monitoring the clustering of the PS sensor lactadherin. Also, colocalization between M1 and a fluorescent PS probe suggest that, in infected cells, the matrix protein can specifically bind to the regions of PM in which PS is clustered. Taken together, our observations provide novel evidence regarding the role of PS-rich domains in tuning M1-lipid and M1-M1 interactions at the PM of infected cells. IMPORTANCE Influenza virus particles assemble at the plasma membranes (PM) of infected cells. This process is orchestrated by the matrix protein M1, which interacts with membrane lipids while binding to the other proteins and genetic material of the virus. Despite its importance, the initial step in virus assembly (i.e., M1-lipid interaction) is still

Regulation of adhesion behavior of murine macrophage using supported lipid membranes displaying tunable mannose domains

International Nuclear Information System (INIS)

Kaindl, T; Oelke, J; Kaufmann, S; Tanaka, M; Pasc, A; Konovalov, O V; Funari, S S; Engel, U; Wixforth, A

2010-01-01

Highly uniform, strongly correlated domains of synthetically designed lipids can be incorporated into supported lipid membranes. The systematic characterization of membranes displaying a variety of domains revealed that the equilibrium size of domains significantly depends on the length of fluorocarbon chains, which can be quantitatively interpreted within the framework of an equivalent dipole model. A mono-dispersive, narrow size distribution of the domains enables us to treat the inter-domain correlations as two-dimensional colloidal crystallization and calculate the potentials of mean force. The obtained results demonstrated that both size and inter-domain correlation can precisely be controlled by the molecular structures. By coupling α-D-mannose to lipid head groups, we studied the adhesion behavior of the murine macrophage (J774A.1) on supported membranes. Specific adhesion and spreading of macrophages showed a clear dependence on the density of functional lipids. The obtained results suggest that such synthetic lipid domains can be used as a defined platform to study how cells sense the size and distribution of functional molecules during adhesion and spreading.

Interfacial electrostatics of poly(vinylamine hydrochloride), poly(diallyldimethylammonium chloride), poly-l-lysine, and poly-l-arginine interacting with lipid bilayers.

Science.gov (United States)

McGeachy, A C; Dalchand, N; Caudill, E R; Li, T; Doğangün, M; Olenick, L L; Chang, H; Pedersen, J A; Geiger, F M

2018-04-25

Charge densities of cationic polymers adsorbed to lipid bilayers are estimated from second harmonic generation (SHG) spectroscopy and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The systems surveyed included poly(vinylamine hydrochloride) (PVAm), poly(diallyldimethylammonium chloride) (PDADMAC), poly-l-lysine (PLL), and poly-l-arginine (PLR), as well as polyalcohol controls. Upon accounting for the number of positive charges associated with each polyelectrolyte, the binding constants and apparent free energies of adsorption as estimated from SHG data are comparable despite differences in molecular masses and molecular structure, with ΔGads values of -61 ± 2, -58 ± 2, -57 ± 1, -52 ± 2, -52 ± 1 kJ mol-1 for PDADMAC400, PDADMAC100, PVAm, PLL, and PLR, respectively. Moreover, we find charge densities for polymer adlayers of approximately 0.3 C m-2 for poly(diallyldimethylammonium chloride) while those of poly(vinylamine) hydrochloride, poly-l-lysine, and poly-l-arginine are approximately 0.2 C m-2. Time-dependent studies indicate that polycation adsorption to supported lipid bilayers is only partially reversible for most of the polymers explored. Poly(diallyldimethylammonium chloride) does not demonstrate reversible binding even over long timescales (>8 hours).

Capturing suboptical dynamic structures in lipid bilayer patches formed from free-standing giant unilamellar vesicles

DEFF Research Database (Denmark)

Bhatia, Tripta; Cornelius, Flemming; Ipsen, John H.

2017-01-01

. The method has been applied to classical lipid raft mixtures in which suboptical domain fluctuations have been imaged in both the liquid-ordered and liquid-disordered membrane phases. High-resolution scanning by atomic force microscopy (AFM) of membranes composed of binary and ternary lipid mixtures...

Lipids, lipid droplets and lipoproteins in their cellular context; an ultrastructural approach

NARCIS (Netherlands)

Mesman, R.J.

2013-01-01

Lipids are essential for cellular life, functioning either organized as bilayer membranes to compartmentalize cellular processes, as signaling molecules or as metabolic energy storage. Our current knowledge on lipid organization and cellular lipid homeostasis is mainly based on biochemical data.

Exploring the raft-hypothesis by probing planar bilayer patches of free-standing giant vesicles at nanoscale resolution, with and without Na,K-ATPase.

Science.gov (United States)

Bhatia, T; Cornelius, F; Ipsen, J H

2016-12-01

The structure of functional lipid domains (rafts) in biological membranes has for long time been unresolved due to their small length scales and transient nature. These cooperative properties of the lipid bilayer matrix are modelled by free-standing giant unilammellar vesicles (GUVs) with well-characterized lipid composition. We review a series of recent advances in preparation and analysis of GUVs, which allows for characterization of small domains by high-resolution imaging techniques. These includes a new GUV preparation method with a desired overall lipid composition achieved by mixing small unilammellar vesicles (SUVs), test of the lipids compositional uniformity in GUVs and swift adsorption of GUVs to solid support by kinetically arresting the lateral structure of membrane prior to collapse for subsequent imaging. The techniques are applied to the analysis of membrane domains in GUVs formed from mixtures of DOPC/DPPC/cholesterol with and without Na,K-ATPase (NKA), a transmembrane protein known to be associated with rafts. Two mechanisms of domain formation are revealed: 1) close to l o /l d phase coexistence, domains in size up to 100nm appear as thermally induced droplet fluctuations, 2) NKA shows interfacial activity and cluster in l o /l d micro-emulsion droplets. Some perspectives for the application of the techniques and the understanding of the nature of raft domains are outlined. Copyright © 2016 Elsevier B.V. All rights reserved.

Mesoscale organization of domains in the plasma membrane - beyond the lipid raft.

Science.gov (United States)

Lu, Stella M; Fairn, Gregory D

2018-04-01

The plasma membrane is compartmentalized into several distinct regions or domains, which show a broad diversity in both size and lifetime. The segregation of lipids and membrane proteins is thought to be driven by the lipid composition itself, lipid-protein interactions and diffusional barriers. With regards to the lipid composition, the immiscibility of certain classes of lipids underlies the "lipid raft" concept of plasmalemmal compartmentalization. Historically, lipid rafts have been described as cholesterol and (glyco)sphingolipid-rich regions of the plasma membrane that exist as a liquid-ordered phase that are resistant to extraction with non-ionic detergents. Over the years the interest in lipid rafts grew as did the challenges with studying these nanodomains. The term lipid raft has fallen out of favor with many scientists and instead the terms "membrane raft" or "membrane nanodomain" are preferred as they connote the heterogeneity and dynamic nature of the lipid-protein assemblies. In this article, we will discuss the classical lipid raft hypothesis and its limitations. This review will also discuss alternative models of lipid-protein interactions, annular lipid shells, and larger membrane clusters. We will also discuss the mesoscale organization of plasmalemmal domains including visible structures such as clathrin-coated pits and caveolae.

Step-wise potential development across the lipid bilayer under external electric fields

Science.gov (United States)

Majhi, Amit Kumar

2018-04-01

Pore formation across the bilayers under external electric field is an important phenomenon, which has numerous applications in biology and bio-engineering fields. However, it is not a ubiquitous event under all field applications. To initiate a pore in the bilayer a particular threshold electric field is required. The electric field alters the intrinsic potential distribution across the bilayer as we as it enhances total potential drop across the bilayer, which causes the pore formation. The intrinsic potential profile has a maximum peak value, which is 0.8 V and it gets enhanced under application of external field, 0.43 V/nm. The peak value becomes 1.4 V when a pore appears in the bilayer and it continues to evolve as along as the external electric field remains switched on.

Effects of Oriented Surface Dipole on Photoconversion Efficiency in an Alkane/Lipid-Hybrid-Bilayer-Based Photovoltaic Model System

KAUST Repository

Liu, Lixia

2013-06-21

When a phospholipid monolayer containing a zinc-coordinated porphyrin species formed atop a self-assembled monolayer of heptadecafluoro-1-decanethiol (CF3(CF2)7(CH2)2SH) is subjected to photoelectrochemical current generation, a significant modulation effect is observed. Compared with devices that contain similar photoactive lipid monolayers but formed on 1-dodecanethiol SAMs, these fluorinated hybrid bilayers produce a >60 % increase in cathodic currents and a similar decrease in anodic currents. Photovoltages recorded from these hybrid bilayers are found to vary in the same fashion. The modulation of photovoltaic responses in these hybrid-bilayer-based devices is explained by the opposite surface dipoles associated with the thiols employed in this study, which in one case (fluorothiol) increase and in another (alkanethiol) decrease the work function of the underlying gold substrates. A similar trend of photovoltage/photocurrent modulation is also observed if fullerene is used as the photoagent in these devices. Our results reveal the intricacy of orientated surface dipole in influencing the photovoltaic processes, and its subtle interplay with other factors related to the photoagents, such as their location and orientation within the organic matrix. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of Oriented Surface Dipole on Photoconversion Efficiency in an Alkane/Lipid-Hybrid-Bilayer-Based Photovoltaic Model System

KAUST Repository

Liu, Lixia; Xie, Hong; Bostic, Heidi E.; Jin, Limei; Best, Michael D.; Zhang, X. Peter; Zhan, Wei

2013-01-01

When a phospholipid monolayer containing a zinc-coordinated porphyrin species formed atop a self-assembled monolayer of heptadecafluoro-1-decanethiol (CF3(CF2)7(CH2)2SH) is subjected to photoelectrochemical current generation, a significant modulation effect is observed. Compared with devices that contain similar photoactive lipid monolayers but formed on 1-dodecanethiol SAMs, these fluorinated hybrid bilayers produce a >60 % increase in cathodic currents and a similar decrease in anodic currents. Photovoltages recorded from these hybrid bilayers are found to vary in the same fashion. The modulation of photovoltaic responses in these hybrid-bilayer-based devices is explained by the opposite surface dipoles associated with the thiols employed in this study, which in one case (fluorothiol) increase and in another (alkanethiol) decrease the work function of the underlying gold substrates. A similar trend of photovoltage/photocurrent modulation is also observed if fullerene is used as the photoagent in these devices. Our results reveal the intricacy of orientated surface dipole in influencing the photovoltaic processes, and its subtle interplay with other factors related to the photoagents, such as their location and orientation within the organic matrix. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Extended synaptotagmins are Ca2+-dependent lipid transfer proteins at membrane contact sites.

Science.gov (United States)

Yu, Haijia; Liu, Yinghui; Gulbranson, Daniel R; Paine, Alex; Rathore, Shailendra S; Shen, Jingshi

2016-04-19

Organelles are in constant communication with each other through exchange of proteins (mediated by trafficking vesicles) and lipids [mediated by both trafficking vesicles and lipid transfer proteins (LTPs)]. It has long been known that vesicle trafficking can be tightly regulated by the second messenger Ca(2+), allowing membrane protein transport to be adjusted according to physiological demands. However, it remains unclear whether LTP-mediated lipid transport can also be regulated by Ca(2+) In this work, we show that extended synaptotagmins (E-Syts), poorly understood membrane proteins at endoplasmic reticulum-plasma membrane contact sites, are Ca(2+)-dependent LTPs. Using both recombinant and endogenous mammalian proteins, we discovered that E-Syts transfer glycerophospholipids between membrane bilayers in the presence of Ca(2+) E-Syts use their lipid-accommodating synaptotagmin-like mitochondrial lipid binding protein (SMP) domains to transfer lipids. However, the SMP domains themselves cannot transport lipids unless the two membranes are tightly tethered by Ca(2+)-bound C2 domains. Strikingly, the Ca(2+)-regulated lipid transfer activity of E-Syts was fully recapitulated when the SMP domain was fused to the cytosolic domain of synaptotagmin-1, the Ca(2+)sensor in synaptic vesicle fusion, indicating that a common mechanism of membrane tethering governs the Ca(2+)regulation of lipid transfer and vesicle fusion. Finally, we showed that microsomal vesicles isolated from mammalian cells contained robust Ca(2+)-dependent lipid transfer activities, which were mediated by E-Syts. These findings established E-Syts as a novel class of LTPs and showed that LTP-mediated lipid trafficking, like vesicular transport, can be subject to tight Ca(2+)regulation.

Preparation and properties of functional mixed-lipid liposomes by γ-ray irradiation

International Nuclear Information System (INIS)

Hosoi, Fumio; Omichi, Hideki; Akama, Kazuhiro; Awai, Kouji; Yano, Yoshihiro; Nakano, Yoshio

1998-01-01

The feature of mixed-lipid liposomes such as polymerization and polymerized liposomes stability were investigated to find means for producing red cells containing hemoglobin inside the liposomes. The surface pressure-area isotherm values of the mixed-lipid monolayer indicated 1-stearoyl-2-(2,4-octadecadienoyl)-glycero-3-phosphocholine (SOPC) to be immiscible in cholesterol (Chol) and stearic acid (SA), and each component to contain separate domains in the bilayer membrane of liposomes. Radiation induced polymerization of mixed-SOPC liposomes was carried out using γ-rays from 60 Co at 4degC to stabilize lipid bilayers. The polymer yield increased significantly by adding Chol and SA to SOPC. The rate of polymerization of SOPC liposomes increased linearly with increasing of dose rate. The molecular weight of the polymer decreased with an increase in irradiation time. Irradiated SOPC/Chol/SA liposome vesicle size was affected by freeze-thawing. The vesicle size did not change when SOPC/Chol/SA was present in the system due to the addition of immiscible saturated 1,2-dipalmitoyl-glycero-3-phosphocholine (DPPC). (author)

Lamellar-lamellar phase separation of phospholipid bilayers induced by salting-in/-out effects

Energy Technology Data Exchange (ETDEWEB)

Hishida, Mafumi [Institute for Integrated Cell-Material Sciences, Kyoto University, Kyoto 606-8501 (Japan); Seto, Hideki, E-mail: hideki.seto@kek.jp [KENS and CMRC, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801 (Japan)

2011-01-01

The multilamellar structure of phospholipid bilayers is stabilized by the interactions between bilayers. Although the lamellar repeat distance is uniquely determined at the balance point of interactions between bilayers, a lamellar-lamellar phase separation, where the two phases with different lamellar repeat distance coexist, has been reported in a case of adding a salt to the aqueous solution of lipids. In order to understand the physical mechanism of the lamellar-lamellar phase separation, the effects of adding monovalent salt on the lamellar structure are studied by visual observation and by small-angle X-ray scattering. Further, a theoretical model based on the mean field theory is introduced and it is concluded that the salting-in and -out effects of lipid bilayers trigger the lamellar-lamellar phase separation.

Lipid-protein interaction induced domains: Kinetics and conformational changes in multicomponent vesicles

Science.gov (United States)

Sreeja, K. K.; Sunil Kumar, P. B.

2018-04-01

The spatio-temporal organization of proteins and the associated morphological changes in membranes are of importance in cell signaling. Several mechanisms that promote the aggregation of proteins at low cell surface concentrations have been investigated in the past. We show, using Monte Carlo simulations, that the affinity of proteins for specific lipids can hasten their aggregation kinetics. The lipid membrane is modeled as a dynamically triangulated surface with the proteins defined as in-plane fields at the vertices. We show that, even at low protein concentrations, strong lipid-protein interactions can result in large protein clusters indicating a route to lipid mediated signal amplification. At high protein concentrations, the domains form buds similar to that seen in lipid-lipid interaction induced phase separation. Protein interaction induced domain budding is suppressed when proteins act as anisotropic inclusions and exhibit nematic orientational order. The kinetics of protein clustering and resulting conformational changes are shown to be significantly different for the isotropic and anisotropic curvature inducing proteins.

Permeability of a Fluid Lipid Bilayer to Short-Chain Alcohols from First Principles.

Science.gov (United States)

Comer, Jeffrey; Schulten, Klaus; Chipot, Christophe

2017-06-13

Computational prediction of membrane permeability to small molecules requires accurate description of both the thermodynamics and kinetics underlying translocation across the lipid bilayer. In this contribution, well-converged, microsecond-long free-energy calculations are combined with a recently developed subdiffusive kinetics framework to describe the membrane permeation of a homologous series of short-tail alcohols, from methanol to 1-butanol, with unprecedented fidelity to the underlying molecular models. While the free-energy profiles exhibit barriers for passage through the center of the bilayer in all cases, the height of these barriers decreases with the length of the aliphatic chain of the alcohol, in quantitative agreement with experimentally determined differential solvation free energies in water and oil. A unique aspect of the subdiffusive model employed herein, which was developed in a previous article, is the determination of a position-dependent fractional order which quantifies the degree to which the motion of the alcohol deviates from classical diffusion along the thickness of the membrane. In the aqueous medium far from the bilayer, this quantity approaches 1.0, the asymptotic limit for purely classical diffusion, whereas it dips below 0.75 near the center of the membrane irrespective of the permeant. Remarkably, the fractional diffusivity near the center of membrane, where its influence on the permeability is the greatest, is similar among the four permeants despite the large difference in molecular weight and lipophilicity between methanol and 1-butanol. The relative permeabilities, which are estimated from the free-energy and fractional diffusivity profiles, are therefore determined predominantly by differences in the former rather than the latter. The predicted relative permeabilities are highly correlated with existing experimental results, albeit they do not agree quantitatively with them. On the other hand, quite unexpectedly, the

Accumulation of raft lipids in T-cell plasma membrane domains engaged in TCR signalling

DEFF Research Database (Denmark)

Zech, Tobias; Ejsing, Christer S.; Gaus, Katharina

2009-01-01

Activating stimuli for T lymphocytes are transmitted through plasma membrane domains that form at T-cell antigen receptor (TCR) signalling foci. Here, we determined the molecular lipid composition of immunoisolated TCR activation domains. We observed that they accumulate cholesterol, sphingomyelin...... and saturated phosphatidylcholine species as compared with control plasma membrane fragments. This provides, for the first time, direct evidence that TCR activation domains comprise a distinct molecular lipid composition reminiscent of liquid-ordered raft phases in model membranes. Interestingly, TCR activation...... domains were also enriched in plasmenyl phosphatidylethanolamine and phosphatidylserine. Modulating the T-cell lipidome with polyunsaturated fatty acids impaired the plasma membrane condensation at TCR signalling foci and resulted in a perturbed molecular lipid composition. These results correlate...

Molecular Transport Studies Through Unsupported Lipid Membranes

Science.gov (United States)

Rock, William; Parekh, Sapun; Bonn, Mischa

2014-03-01

Dendrimers, spherical polymeric nanoparticles made from branched monomers around a central core, show great promise as drug delivery vehicles. Dendrimer size, core contents, and surface functionality can be synthetically tuned, providing unprecedented versatility. Polyamidoamine (PAMAM) dendrimers have been shown to enter cells; however, questions remain about their biophysical interactions with the cell membrane, specifically about the presence and size of transient pores. We monitor dendrimer-lipid bilayer interactions using unsupported black lipid membranes (BLMs) as model cell membranes. Custom bilayer slides contain two vertically stacked aqueous chambers separated by a 25 μm Teflon sheet with a 120 μm aperture where the bilayer is formed. We vary the composition of model membranes (cholesterol content and lipid phase) to create biomimetic systems and study the interaction of PAMAM G6 and G3 dendrimers with these bilayers. Dendrimers, dextran cargo, and bilayers are monitored and quantified using time-lapse fluorescence imaging. Electrical capacitance measurements are simultaneously recorded to determine if the membrane is porous, and the pore size is deduced by monitoring transport of fluorescent dextrans of increasing molecular weight. These experiments shed light on the importance of cholesterol content and lipid phase on the interaction of dendrimer nanoparticles with membranes.

Possible mechanism of adhesion in a mica supported phospholipid bilayer

International Nuclear Information System (INIS)

Pertsin, Alexander; Grunze, Michael

2014-01-01

Phospholipid bilayers supported on hydrophilic solids like silica and mica play a substantial role in fundamental studies and technological applications of phospholipid membranes. In both cases the molecular mechanism of adhesion between the bilayer and the support is of primary interest. Since the possibilities of experimental methods in this specific area are rather limited, the methods of computer simulation acquire great importance. In this paper we use the grand canonical Monte Carlo technique and an atomistic force field to simulate the behavior of a mica supported phospholipid bilayer in pure water as a function of the distance between the bilayer and the support. The simulation reveals a possible adhesion mechanism, where the adhesion is due to individual lipid molecules that protrude from the bilayer and form widely spaced links with the support. Simultaneously, the bilayer remains separated from the bilayer by a thin water interlayer which maintains the bilayer fluidity

Impact of amphiphilic molecules on the structure and stability of homogeneous sphingomyelin bilayer: Insights from atomistic simulations

Science.gov (United States)

Kumari, Pratibha; Kaur, Supreet; Sharma, Shobha; Kashyap, Hemant K.

2018-04-01

Modulation of lipid membrane properties due to the permeation of amphiphiles is an important biological process pertaining to many applications in the field of pharmaceutics, toxicology, and biotechnology. Sphingolipids are both structural and functional lipids that constitute an important component of mechanically stable and chemically resistant outer leaflets of plasma membranes. Here, we present an atomistic molecular dynamics simulation study to appreciate the concentration-dependent effects of small amphiphilic molecules, such as ethanol, acetone, and dimethyl sulfoxide (DMSO), on the structure and stability of a fully hydrated homogeneous N-palmitoyl-sphingomyelin (PSM) bilayer. The study reveals an increase in the lateral expansion of the bilayer along with disordering of the hydrophobic lipid tails on increasing the concentration of ethanol. At higher concentrations of ethanol, rupturing of the bilayer is quite evident through the analysis of partial electron density profiles and lipid tail order parameters. For ethanol containing systems, permeation of water molecules in the hydrophobic part of the bilayer is allowed through local defects made due to the entry of ethanol molecules via ethanol-ethanol and ethanol-PSM hydrogen bonds. Moreover, the extent of PSM-PSM hydrogen bonding decreases with increasing ethanol concentration. On the other hand, acetone and DMSO exhibit minimal effects on the stability of the PSM bilayer at their lower concentrations, but at higher concentrations they tend to enhance the stability of the bilayer. The simulated potential of mean force (PMF) profiles for the translocation of the three solutes studied reveal that the free-energy of transfer of an ethanol molecule across the PSM lipid head region is lower than that for acetone and DMSO molecules. However, highest free-energy rise in the core hydrophobic part of the bilayer is observed for the DMSO molecule, whereas the ethanol and acetone PMF profiles show a lower barrier in

Thermotropic and Barotropic Phase Behavior of Phosphatidylcholine Bilayers

Directory of Open Access Journals (Sweden)

Nobutake Tamai

2013-01-01

Full Text Available Bilayers formed by phospholipids are frequently used as model biological membranes in various life science studies. A characteristic feature of phospholipid bilayers is to undergo a structural change called a phase transition in response to environmental changes of their surroundings. In this review, we focus our attention on phase transitions of some major phospholipids contained in biological membranes, phosphatidylcholines (PCs, depending on temperature and pressure. Bilayers of dipalmitoylphosphatidylcholine (DPPC, which is the most representative lipid in model membrane studies, will first be explained. Then, the bilayer phase behavior of various kinds of PCs with different molecular structures is revealed from the temperature–pressure phase diagrams, and the difference in phase stability among these PC bilayers is discussed in connection with the molecular structure of the PC molecules. Furthermore, the solvent effect on the phase behavior is also described briefly.

General model of phospholipid bilayers in fluid phase within the single chain mean field theory

Energy Technology Data Exchange (ETDEWEB)

Guo, Yachong; Baulin, Vladimir A. [Departament d’Enginyeria Química, Universitat Rovira i Virgili, Av. dels Paisos Catalans 26, 43007 Tarragona (Spain); Pogodin, Sergey [Institute of Chemical Research of Catalonia, ICIQ, Av. Paisos Catalans 16, 43007 Tarragona (Spain)

2014-05-07

Coarse-grained model for saturated phospholipids: 1,2-didecanoyl-sn-glycero-3-phosphocholine (DCPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and unsaturated phospholipids: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2- dioleoyl-sn-glycero-3-phosphocholine (DOPC) is introduced within the single chain mean field theory. A single set of parameters adjusted for DMPC bilayers gives an adequate description of equilibrium and mechanical properties of a range of saturated lipid molecules that differ only in length of their hydrophobic tails and unsaturated (POPC, DOPC) phospholipids which have double bonds in the tails. A double bond is modeled with a fixed angle of 120°, while the rest of the parameters are kept the same as saturated lipids. The thickness of the bilayer and its hydrophobic core, the compressibility, and the equilibrium area per lipid correspond to experimentally measured values for each lipid, changing linearly with the length of the tail. The model for unsaturated phospholipids also fetches main thermodynamical properties of the bilayers. This model is used for an accurate estimation of the free energies of the compressed or stretched bilayers in stacks or multilayers and gives reasonable estimates for free energies. The proposed model may further be used for studies of mixtures of lipids, small molecule inclusions, interactions of bilayers with embedded proteins.

Interaction of cholesterol-conjugated ionizable amino lipids with biomembranes: lipid polymorphism, structure-activity relationship, and implications for siRNA delivery.

Science.gov (United States)

Zhang, Jingtao; Fan, Haihong; Levorse, Dorothy A; Crocker, Louis S

2011-08-02

Delivery of siRNA is a major obstacle to the advancement of RNAi as a novel therapeutic modality. Lipid nanoparticles (LNP) consisting of ionizable amino lipids are being developed as an important delivery platform for siRNAs, and significant efforts are being made to understand the structure-activity relationship (SAR) of the lipids. This article uses a combination of small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) to evaluate the interaction between cholesterol-conjugated ionizable amino lipids and biomembranes, focusing on an important area of lipid SAR--the ability of lipids to destabilize membrane bilayer structures and facilitate endosomal escape. In this study, cholesterol-conjugated amino lipids were found to be effective in increasing the order of biomembranes and also highly effective in inducing phase changes in biological membranes in vitro (i.e., the lamellar to inverted hexagonal phase transition). The phase transition temperatures, determined using SAXS and DSC, serve as an indicator for ranking the potency of lipids to destabilize endosomal membranes. It was found that the bilayer disruption ability of amino lipids depends strongly on the amino lipid concentration in membranes. Amino lipids with systematic variations in headgroups, the extent of ionization, tail length, the degree of unsaturation, and tail asymmetry were evaluated for their bilayer disruption ability to establish SAR. Overall, it was found that the impact of these lipid structure changes on their bilayer disruption ability agrees well with the results from a conceptual molecular "shape" analysis. Implications of the findings from this study for siRNA delivery are discussed. The methods reported here can be used to support the SAR screening of cationic lipids for siRNA delivery, and the information revealed through the study of the interaction between cationic lipids and biomembranes will contribute significantly to the design of more efficient si

pH sensing by lipids in membranes: The fundamentals of pH-driven migration, polarization and deformations of lipid bilayer assemblies.

Science.gov (United States)

Angelova, Miglena I; Bitbol, Anne-Florence; Seigneuret, Michel; Staneva, Galya; Kodama, Atsuji; Sakuma, Yuka; Kawakatsu, Toshihiro; Imai, Masayuki; Puff, Nicolas

2018-03-06

Most biological molecules contain acido-basic groups that modulate their structure and interactions. A consequence is that pH gradients, local heterogeneities and dynamic variations are used by cells and organisms to drive or regulate specific biological functions including energetic metabolism, vesicular traffic, migration and spatial patterning of tissues in development. While the direct or regulatory role of pH in protein function is well documented, the role of hydrogen and hydroxyl ions in modulating the properties of lipid assemblies such as bilayer membranes is only beginning to be understood. Here, we review approaches using artificial lipid vesicles that have been instrumental in providing an understanding of the influence of pH gradients and local variations on membrane vectorial motional processes: migration, membrane curvature effects promoting global or local deformations, crowding generation by segregative polarization processes. In the case of pH induced local deformations, an extensive theoretical framework is given and an application to a specific biological issue, namely the structure and stability of mitochondrial cristae, is described. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo. Copyright © 2018 Elsevier B.V. All rights reserved.

Membrane interaction of antimicrobial peptides using E. coli lipid extract as model bacterial cell membranes and SFG spectroscopy.

Science.gov (United States)

Soblosky, Lauren; Ramamoorthy, Ayyalusamy; Chen, Zhan

2015-04-01

Supported lipid bilayers are used as a convenient model cell membrane system to study biologically important molecule-lipid interactions in situ. However, the lipid bilayer models are often simple and the acquired results with these models may not provide all pertinent information related to a real cell membrane. In this work, we use sum frequency generation (SFG) vibrational spectroscopy to study molecular-level interactions between the antimicrobial peptides (AMPs) MSI-594, ovispirin-1 G18, magainin 2 and a simple 1,2-dipalmitoyl-d62-sn-glycero-3-phosphoglycerol (dDPPG)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) bilayer. We compared such interactions to those between the AMPs and a more complex dDPPG/Escherichia coli (E. coli) polar lipid extract bilayer. We show that to fully understand more complex aspects of peptide-bilayer interaction, such as interaction kinetics, a heterogeneous lipid composition is required, such as the E. coli polar lipid extract. The discrepancy in peptide-bilayer interaction is likely due in part to the difference in bilayer charge between the two systems since highly negative charged lipids can promote more favorable electrostatic interactions between the peptide and lipid bilayer. Results presented in this paper indicate that more complex model bilayers are needed to accurately analyze peptide-cell membrane interactions and demonstrates the importance of using an appropriate lipid composition to study AMP interaction properties. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Use of isothermal titration calorimetry to study the interaction of short-chain alcohols with lipid membranes

DEFF Research Database (Denmark)

Trandum, Christa; Westh-Andersen, Peter; Jørgensen, Kent

1999-01-01

of short-chain alcohols on Lipid bilayers. isothermal titration calorimetry (ITC) has been used to determine the energy involved in the association of the alcohols with lipid bilayers. Pure unilamellar DMPC liposomes and DMPC liposomes incorporated with different amounts of cholesterol, sphingomyelin...... dependent on the lipid bilayer composition. In the presence of high concentrations of cholesterol, the binding enthalpy of ethanol is decreased, whereas the presence of ceramides enhances the enthalpic response of the lipid bilayer to ethanol. Isothermal titration calorimetry offers a new methodology...

Electron paramagnetic resonance (EPR spectral components of spin-labeled lipids in saturated phospholipid bilayers: effect of cholesterol

Directory of Open Access Journals (Sweden)

Heverton Silva Camargos

2013-01-01

Full Text Available Electron paramagnetic resonance (EPR spectroscopy was used to study the main structural accommodations of spin labels in bilayers of saturated phosphatidylcholines with acyl chain lengths ranging from 16 to 22 carbon atoms. EPR spectra allowed the identification of two distinct spectral components in thermodynamic equilibrium at temperatures below and above the main phase transition. An accurate analysis of EPR spectra, using two fitting programs, enabled determination of the thermodynamic profile for these major probe accommodations. Focusing the analysis on two-component EPR spectra of a spin-labeled lipid, the influence of 40 mol % cholesterol in DPPC was studied.

Effect of free cholesterol on incorporation of triolein in phospholipid bilayers

International Nuclear Information System (INIS)

Spooner, P.J.R.; Small, D.M.

1987-01-01

Triacylglycerols are the major substrates for lipolytic enzymes that act at the surface of emulsion-like particles such as triglyceride-rich lipoproteins, chylomicrons, and intracellular lipid droplets. This study examines the effect of cholesterol on the solubility of a triacylglycerol, triolein, in phospholipid surfaces. Solubilities of [carbonyl- 13 C] triolein in phospholipid bilayer vesicles containing between 0 and 50 mol % free cholesterol, prepared by cosonication, were measured by 13 C NMR. The carbonyl resonances from bilayer-incorporated triglyceride were shifted downfield in the 13 C NMR spectra from those corresponding to excess, nonincorporated material. This enabled solubilities to be determined directly from carbonyl peak intensities at most cholesterol concentration. The bilayer solubility of triolein was inversely proportional to the cholesterol/phospholipid mole ratio. In pure phospholipid vesicles the triolein solubility was 2.2 mol %. The triglyceride incorporation decreased to 1.1 mol % at a cholesterol/phospholipid mole ratio of 0.5, and at a mole ratio of 1.0 for the bilayer lipids, the triolein solubility was reduced to just 0.15 mol %. The effects of free cholesterol were more pronounced and progressive than observed previously on the bilayer solubility of cholestery oleate. As with cholesteryl oleate, they suggest that cholesterol also displaces solubilized triglyceride to deeper regions of the bilayer

Structure and dynamics of POPC bilayers in water solutions of room temperature ionic liquids

International Nuclear Information System (INIS)

Benedetto, Antonio; Bingham, Richard J.; Ballone, Pietro

2015-01-01

Molecular dynamics simulations in the NPT ensemble have been carried out to investigate the effect of two room temperature ionic liquids (RTILs), on stacks of phospholipid bilayers in water. We consider RTIL compounds consisting of chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF 6 ]) salts of the 1-buthyl-3-methylimidazolium ([bmim] + ) cation, while the phospholipid bilayer is made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Our investigations focus on structural and dynamical properties of phospholipid and water molecules that could be probed by inelastic and quasi-elastic neutron scattering measurements. The results confirm the fast incorporation of [bmim] + into the lipid phase already observed in previous simulations, driven by the Coulomb attraction of the cation for the most electronegative oxygens in the POPC head group and by sizeable dispersion forces binding the neutral hydrocarbon tails of [bmim] + and of POPC. The [bmim] + absorption into the bilayer favours the penetration of water into POPC, causes a slight but systematic thinning of the bilayer, and further stabilises hydrogen bonds at the lipid/water interface that already in pure samples (no RTIL) display a lifetime much longer than in bulk water. On the other hand, the effect of RTILs on the diffusion constant of POPC (D POPC ) does not reveal a clearly identifiable trend, since D POPC increases upon addition of [bmim][Cl] and decreases in the [bmim][PF 6 ] case. Moreover, because of screening, the electrostatic signature of each bilayer is only moderately affected by the addition of RTIL ions in solution. The analysis of long wavelength fluctuations of the bilayers shows that RTIL sorption causes a general decrease of the lipid/water interfacial tension and bending rigidity, pointing to the destabilizing effect of RTILs on lipid bilayers

Structure and dynamics of POPC bilayers in water solutions of room temperature ionic liquids

Energy Technology Data Exchange (ETDEWEB)

Benedetto, Antonio [School of Physics, University College Dublin, Dublin 4 (Ireland); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen (Switzerland); Bingham, Richard J. [York Centre for Complex Systems Analysis, University of York, York YO10 5GE (United Kingdom); Ballone, Pietro [Center for Life Nano Science @Sapienza, Istituto Italiano di Tecnologia (IIT), 00185 Roma (Italy); Department of Physics, Università di Roma “La Sapienza,” 00185 Roma (Italy)

2015-03-28

Molecular dynamics simulations in the NPT ensemble have been carried out to investigate the effect of two room temperature ionic liquids (RTILs), on stacks of phospholipid bilayers in water. We consider RTIL compounds consisting of chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF{sub 6}]) salts of the 1-buthyl-3-methylimidazolium ([bmim]{sup +}) cation, while the phospholipid bilayer is made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Our investigations focus on structural and dynamical properties of phospholipid and water molecules that could be probed by inelastic and quasi-elastic neutron scattering measurements. The results confirm the fast incorporation of [bmim]{sup +} into the lipid phase already observed in previous simulations, driven by the Coulomb attraction of the cation for the most electronegative oxygens in the POPC head group and by sizeable dispersion forces binding the neutral hydrocarbon tails of [bmim]{sup +} and of POPC. The [bmim]{sup +} absorption into the bilayer favours the penetration of water into POPC, causes a slight but systematic thinning of the bilayer, and further stabilises hydrogen bonds at the lipid/water interface that already in pure samples (no RTIL) display a lifetime much longer than in bulk water. On the other hand, the effect of RTILs on the diffusion constant of POPC (D{sub POPC}) does not reveal a clearly identifiable trend, since D{sub POPC} increases upon addition of [bmim][Cl] and decreases in the [bmim][PF{sub 6}] case. Moreover, because of screening, the electrostatic signature of each bilayer is only moderately affected by the addition of RTIL ions in solution. The analysis of long wavelength fluctuations of the bilayers shows that RTIL sorption causes a general decrease of the lipid/water interfacial tension and bending rigidity, pointing to the destabilizing effect of RTILs on lipid bilayers.

NMR study of the interactions of polymyxin B, gramicidin S, and valinomycin with dimyristoyllecithin bilayers

International Nuclear Information System (INIS)

Zidovetzki, R.; Banerjee, U.; Harrington, D.W.; Chan, S.I.

1988-01-01

The interactions of three polypeptide antibiotics (polymyxin B, gramicidin S, and valinomycin) with artificial lecithin membranes were studied by nuclear magnetic resonance (NMR). Combination of 31 P and 2 H NMR allowed observation of perturbations of the bilayer membrane structure induced by each of the antibiotics in the regions of the polar headgroups and acyl side chains of the phospholipids. The comparative study of the effects of these membrane-active antibiotics and the lipid bilayer structure demonstrated distinct types of antibiotic-membrane interactions in each case. Thus, the results showed the absence of interaction of polymyxin B with the dimyristoyllecithin membranes. In contrast, gramicidin S exhibited strong interaction with the lipid above the gel to liquid-crystalline phase transition temperature: disordering of the acyl side chains was evident. Increasing the concentration of gramicidin S led to disintegration of the bilayer membrane structure. At a molar ratio of 1:16 of gramicidin S to lecithin, the results are consistent with coexistence of gel and liquid-crystalline phases of the phospholipids near the phase transition temperature. Valinomycin decreased the phase transition temperature of the lipids and increased the order parameters of the lipid side chains. Such behavior is consistent with penetration of the valinomycin molecule into the interior of the lipid bilayers

BAR domain proteins regulate Rho GTPase signaling.

Science.gov (United States)

Aspenström, Pontus

2014-01-01

BAR proteins comprise a heterogeneous group of multi-domain proteins with diverse biological functions. The common denominator is the Bin-Amphiphysin-Rvs (BAR) domain that not only confers targeting to lipid bilayers, but also provides scaffolding to mold lipid membranes into concave or convex surfaces. This function of BAR proteins is an important determinant in the dynamic reconstruction of membrane vesicles, as well as of the plasma membrane. Several BAR proteins function as linkers between cytoskeletal regulation and membrane dynamics. These links are provided by direct interactions between BAR proteins and actin-nucleation-promoting factors of the Wiskott-Aldrich syndrome protein family and the Diaphanous-related formins. The Rho GTPases are key factors for orchestration of this intricate interplay. This review describes how BAR proteins regulate the activity of Rho GTPases, as well as how Rho GTPases regulate the function of BAR proteins. This mutual collaboration is a central factor in the regulation of vital cellular processes, such as cell migration, cytokinesis, intracellular transport, endocytosis, and exocytosis.

Computational Design of Multi-component Bio-Inspired Bilayer Membranes

Directory of Open Access Journals (Sweden)

Evan Koufos

2014-04-01

Full Text Available Our investigation is motivated by the need to design bilayer membranes with tunable interfacial and mechanical properties for use in a range of applications, such as targeted drug delivery, sensing and imaging. We draw inspiration from biological cell membranes and focus on their principal constituents. In this paper, we present our results on the role of molecular architecture on the interfacial, structural and dynamical properties of bio-inspired membranes. We focus on four lipid architectures with variations in the head group shape and the hydrocarbon tail length. Each lipid species is composed of a hydrophilic head group and two hydrophobic tails. In addition, we study a model of the Cholesterol molecule to understand the interfacial properties of a bilayer membrane composed of rigid, single-tail molecular species. We demonstrate the properties of the bilayer membranes to be determined by the molecular architecture and rigidity of the constituent species. Finally, we demonstrate the formation of a stable mixed bilayer membrane composed of Cholesterol and one of the phospholipid species. Our approach can be adopted to design multi-component bilayer membranes with tunable interfacial and mechanical properties. We use a Molecular Dynamics-based mesoscopic simulation technique called Dissipative Particle Dynamics that resolves the molecular details of the components through soft-sphere coarse-grained models and reproduces the hydrodynamic behavior of the system over extended time scales.

El Tor hemolysin of Vibrio cholerae O1 forms channels in planar lipid bilayer membranes.

Science.gov (United States)

Ikigai, H; Ono, T; Iwata, M; Nakae, T; Shimamura, T

1997-05-15

We investigated the channel formation by El Tor hemolysin (molecular mass, 65 kDa) of Vibrio cholerae O1 biotype El Tor in planar lipid bilayers. The El Tor hemolysin channel exhibited asymmetric and hyperbolic membrane current with increasing membrane potential, meaning that the channel is voltage dependent. The zero-current membrane potential measured in KCI solution showed that permeability ratio PK+/PCl- was 0.16, indicating that the channel is 6-fold more anion selective over cation. The hemolysin channel frequently flickered in the presence of divalent cations, suggesting that the channel spontaneously opens and closes. These data imply that the El Tor hemolysin damages target cells by the formation of transmembrane channels and, consequently, is the cause of osmotic cytolysis.

Small-angle neutron scattering from multilamellar lipid bilayers: Theory, model, and experiment

DEFF Research Database (Denmark)

Lemmich, Jesper; Mortensen, Kell; Ipsen, John Hjorth

1996-01-01

Small-angle neutron scattering data obtained from fully hydrated, multilamellar phospholipid bilayers with deuterated acyl chains of different length are presented and analyzed within a paracrystalline theory and a geometric model that permit the bilayer structure to be determined under conditions...... of temperature for the lamellar repeat distance, the hydrophobic bilayer thickness, as well as the thickness of the aqueous and polar head group region. In addition to these geometric parameters the analysis permits determination of molecular cross-sectional area, number of interlamellar water molecules, as well...

The molecular-scale arrangement and mechanical strength of phospholipid/cholesterol mixed bilayers investigated by frequency modulation atomic force microscopy in liquid

Energy Technology Data Exchange (ETDEWEB)

Asakawa, Hitoshi; Fukuma, Takeshi [Frontier Science Organization, Kanazawa University, Kakuma-machi, 920-1192 Kanazawa (Japan)], E-mail: hi_asa@staff.kanazawa-u.ac.jp, E-mail: fukuma@staff.kanazawa-u.ac.jp

2009-07-01

Cholesterols play key roles in controlling molecular fluidity in a biological membrane, yet little is known about their molecular-scale arrangements in real space. In this study, we have directly imaged lipid-cholesterol complexes in a model biological membrane consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterols by frequency modulation atomic force microscopy (FM-AFM) in phosphate buffer solution. FM-AFM images of a DPPC/cholesterol bilayer in the liquid-ordered phase showed higher energy dissipation values compared to those measured on a nanoscale DPPC domain in the gel phase, reflecting the increased molecular fluidity due to the insertion of cholesterols. Molecular-resolution FM-AFM images of a DPPC/cholesterol bilayer revealed the existence of a rhombic molecular arrangement (lattice constants: a = 0.46 nm, b = 0.71 nm) consisting of alternating rows of DPPC and cholesterols as well as the increased defect density and reduced molecular ordering. The mechanical strength of a DPPC/cholesterol bilayer was quantitatively evaluated by measuring a loading force required to penetrate the membrane with an AFM tip. The result revealed the significant decrease of mechanical strength upon insertion of cholesterols. Based on the molecular-scale arrangement found in this study, we propose a model to explain the reduced mechanical strength in relation to the formation of lipid-ion networks.

The molecular-scale arrangement and mechanical strength of phospholipid/cholesterol mixed bilayers investigated by frequency modulation atomic force microscopy in liquid

International Nuclear Information System (INIS)

Asakawa, Hitoshi; Fukuma, Takeshi

2009-01-01

Cholesterols play key roles in controlling molecular fluidity in a biological membrane, yet little is known about their molecular-scale arrangements in real space. In this study, we have directly imaged lipid-cholesterol complexes in a model biological membrane consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterols by frequency modulation atomic force microscopy (FM-AFM) in phosphate buffer solution. FM-AFM images of a DPPC/cholesterol bilayer in the liquid-ordered phase showed higher energy dissipation values compared to those measured on a nanoscale DPPC domain in the gel phase, reflecting the increased molecular fluidity due to the insertion of cholesterols. Molecular-resolution FM-AFM images of a DPPC/cholesterol bilayer revealed the existence of a rhombic molecular arrangement (lattice constants: a = 0.46 nm, b = 0.71 nm) consisting of alternating rows of DPPC and cholesterols as well as the increased defect density and reduced molecular ordering. The mechanical strength of a DPPC/cholesterol bilayer was quantitatively evaluated by measuring a loading force required to penetrate the membrane with an AFM tip. The result revealed the significant decrease of mechanical strength upon insertion of cholesterols. Based on the molecular-scale arrangement found in this study, we propose a model to explain the reduced mechanical strength in relation to the formation of lipid-ion networks.

An overview of molecular dynamics simulations of oxidized lipid systems, with a comparison of ELBA and MARTINI force fields for coarse grained lipid simulations

DEFF Research Database (Denmark)

Siani, Pablo; de Souza, R M; Dias, L G

2016-01-01

our new data of all-atom and coarse-grained simulations of hydroperoxidized lipid monolayer and bilayer systems and (iii) provide a comparison of the MARTINI and ELBA coarse grained force fields for lipid bilayer systems. We show that the better electrostatic treatment of interactions in ELBA is able...

A mutational analysis of the endophilin-A N-BAR domain performed in living flies

DEFF Research Database (Denmark)

Jung, Anita G; Mønsted, Christina Labarrera; Jansen, Anna M

2010-01-01

BAR domain clearly affected adult flies, larval endophilin function was surprisingly resistant to mutagenesis. Previous reports have stressed the importance of a central appendage on the convex BAR surface, which forms a hydrophobic ridge able to directly insert into the lipid bilayer. We found......-function studies of the endophilin-A BAR domain have almost exclusively been made in reduced systems, either in vitro or ex vivo in cultured cells. To extend and complement this work, we have analyzed the role played by the structural features of the endophilin-A BAR domain in Drosophila in vivo. METHODOLOGY...

The OpenPicoAmp: an open-source planar lipid bilayer amplifier for hands-on learning of neuroscience.

Science.gov (United States)

Shlyonsky, Vadim; Dupuis, Freddy; Gall, David

2014-01-01

Understanding the electrical biophysical properties of the cell membrane can be difficult for neuroscience students as it relies solely on lectures of theoretical models without practical hands on experiments. To address this issue, we developed an open-source lipid bilayer amplifier, the OpenPicoAmp, which is appropriate for use in introductory courses in biophysics or neurosciences at the undergraduate level, dealing with the electrical properties of the cell membrane. The amplifier is designed using the common lithographic printed circuit board fabrication process and off-the-shelf electronic components. In addition, we propose a specific design for experimental chambers allowing the insertion of a commercially available polytetrafluoroethylene film. We provide a complete documentation allowing to build the amplifier and the experimental chamber. The students hand-out giving step-by step instructions to perform a recording is also included. Our experimental setup can be used in basic experiments in which students monitor the bilayer formation by capacitance measurement and record unitary currents produced by ionic channels like gramicidin A dimers. Used in combination with a low-cost data acquisition board this system provides a complete solution for hands-on lessons, therefore improving the effectiveness in teaching basic neurosciences or biophysics.

Life as a matter of fat : lipids in a membrane biophysics perspective

CERN Document Server

Mouritsen, Ole G

2016-01-01

The present book gives a multi-disciplinary perspective on the physics of life and the particular role played by lipids (fats) and the lipid-bilayer component of cell membranes. The emphasis is on the physical properties of lipid membranes seen as soft and molecularly structured interfaces. By combining and synthesizing insights obtained from a variety of recent studies, an attempt is made to clarify what membrane structure is and how it can be quantitatively described. Furthermore, it is shown how biological function mediated by membranes is controlled by lipid membrane structure and organization on length scales ranging from the size of the individual molecule, across molecular assemblies of proteins and lipid domains in the range of nanometers, to the size of whole cells. Applications of lipids in nanotechnology and biomedicine are also described.   The first edition of the present book was published in 2005 when lipidomics was still very much an emerging science and lipids about to be recognized as being...

Photolithographic Polymerization of Diacetylene-Containing Phospholipid Bilayers Studied by Multimode Atomic Force Microscopy

NARCIS (Netherlands)

Morigaki, Kenichi; Schönherr, Holger; Frank, Curtis W.; Knoll, Wolfgang

2003-01-01

Photopolymerization of the diacetylene-containing phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (1) in substrate-supported planar lipid bilayers (SPBs) has been studied by using multimode atomic force microscopy (AFM). Monolayers and bilayers of 1 have been transferred onto

Chitosan derivatives targeting lipid bilayers: Synthesis, biological activity and interaction with model membranes.

Science.gov (United States)

Martins, Danubia Batista; Nasário, Fábio Domingues; Silva-Gonçalves, Laiz Costa; de Oliveira Tiera, Vera Aparecida; Arcisio-Miranda, Manoel; Tiera, Marcio José; Dos Santos Cabrera, Marcia Perez

2018-02-01

The antimicrobial activity of chitosan and derivatives to human and plant pathogens represents a high-valued prospective market. Presently, two low molecular weight derivatives, endowed with hydrophobic and cationic character at different ratios were synthesized and characterized. They exhibit antimicrobial activity and increased performance in relation to the intermediate and starting compounds. However, just the derivative with higher cationic character showed cytotoxicity towards human cervical carcinoma cells. Considering cell membranes as targets, the mode of action was investigated through the interaction with model lipid vesicles mimicking bacterial, tumoral and erythrocyte membranes. Intense lytic activity and binding are demonstrated for both derivatives in anionic bilayers. The less charged compound exhibits slightly improved selectivity towards bacterial model membranes, suggesting that balancing its hydrophobic/hydrophilic character may improve efficiency. Observing the aggregation of vesicles, we hypothesize that the "charge cluster mechanism", ascribed to some antimicrobial peptides, could be applied to these chitosan derivatives. Copyright © 2017 Elsevier Ltd. All rights reserved.

Aggregation of Aß(25-35 on DOPC and DOPC/DHA bilayers: an atomic force microscopy study.

Directory of Open Access Journals (Sweden)

Matilde Sublimi Saponetti

Full Text Available β amyloid peptide plays an important role in both the manifestation and progression of Alzheimer disease. It has a tendency to aggregate, forming low-molecular weight soluble oligomers, higher-molecular weight protofibrillar oligomers and insoluble fibrils. The relative importance of these single oligomeric-polymeric species, in relation to the morbidity of the disease, is currently being debated. Here we present an Atomic Force Microscopy (AFM study of Aβ(25-35 aggregation on hydrophobic dioleoylphosphatidylcholine (DOPC and DOPC/docosahexaenoic 22∶6 acid (DHA lipid bilayers. Aβ(25-35 is the smallest fragment retaining the biological activity of the full-length peptide, whereas DOPC and DOPC/DHA lipid bilayers were selected as models of cell-membrane environments characterized by different fluidity. Our results provide evidence that in hydrophobic DOPC and DOPC/DHA lipid bilayers, Aβ(25-35 forms layered aggregates composed of mainly annular structures. The mutual interaction between annular structures and lipid surfaces end-results into a membrane solubilization. The presence of DHA as a membrane-fluidizing agent is essential to protect the membrane from damage caused by interactions with peptide aggregates; to reduces the bilayer defects where the delipidation process starts.

Mechanics of Lipid Bilayer Membranes

Science.gov (United States)

Powers, Thomas R.

All cells have membranes. The plasma membrane encapsulates the cell's interior, acting as a barrier against the outside world. In cells with nuclei (eukaryotic cells), membranes also form internal compartments (organelles) which carry out specialized tasks, such as protein modification and sorting in the case of the Golgi apparatus, and ATP production in the case of mitochondria. The main components of membranes are lipids and proteins. The proteins can be channels, carriers, receptors, catalysts, signaling molecules, or structural elements, and typically contribute a substantial fraction of the total membrane dry weight. The equilibrium properties of pure lipid membranes are relatively well-understood, and will be the main focus of this article. The framework of elasticity theory and statistical mechanics that we will develop will serve as the foundation for understanding biological phenomena such as the nonequilibrium behavior of membranes laden with ion pumps, the role of membrane elasticity in ion channel gating, and the dynamics of vesicle fission and fusion. Understanding the mechanics of lipid membranes is also important for drug encapsulation and delivery.

Nonideal mixing in multicomponent lipid/detergent systems

International Nuclear Information System (INIS)

Tsamaloukas, Alekos; Szadkowska, Halina; Heerklotz, Heiko

2006-01-01

A detailed understanding of the mixing properties of membranes to which detergents are added is mandatory for improving the application and interpretation of detergent based protein or lipid extraction assays. For Triton X-100 (TX-100), a nonionic detergent frequently used in the process of solubilizing and purifying membrane proteins and lipids, we present here a detailed study of the mixing properties of binary and ternary lipid mixtures by means of high-sensitivity isothermal titration calorimetry (ITC). To this end the partitioning thermodynamics of TX-100 molecules from the aqueous phase to lipid bilayers composed of various mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), egg-sphingomyelin (SM), and cholesterol (cho) are characterized. Composition-dependent partition coefficients K are analysed within the frame of a thermodynamic model developed to describe nonideal mixing in multicomponent lipid/detergent systems. The results imply that POPC, fluid SM, and TX-100 mix almost ideally (nonideality parameters ρ α/β SM/cho ≤-6RT) and unfavourable PC/cho interactions (ρ PC/cho = 2RT) may under certain conditions cause POPC/TX-100-enriched domains to segregate from SM/cho-enriched ones. TX-100/cho contacts are unfavourable (ρ cho/TX = 4RT), so the system tends to avoid them. That means, addition of TX-100 promotes the separation of SM/cho-rich from PC/TX-100-rich domains. It appears that cho/detergent interactions are crucial governing the abundance and composition of detergent-resistant membrane patches

Salt-induced effects on natural and inverse DPPC lipid membranes: Molecular dynamics simulation.

Science.gov (United States)

Rezaei Sani, Seyed Mojtaba; Akhavan, Mojdeh; Jalili, Seifollah

2018-08-01

Molecular dynamics (MD) simulations of a dipalmitoylphosphatidylcholine (DPPC) bilayer and its neutral inverse-phosphocholine equivalent (DPCPe) were performed to find salt-induced effects on their surface structure and the nature of ion-lipid interactions. We found that the area per lipid is not considerably affected by the inversion, but the deuterium order parameter of carbon atoms in the region of carbonyl carbons changes dramatically. MD simulations indicate that Ca 2+ ions can bind to the surface of both DPPC and DPCPe membranes, but K + ions do not bind to them. In the case of Na + , however, the ions can bind to natural lipids but not to the inverse ones. Also, our results demonstrate that the hydration level of CPe bilayers is substantially lower than PC bilayers and the averaged orientation of water dipoles in the region of CPe headgroups is effectively inverted compared to PC lipids. This might be important in the interaction of the bilayer with its biological environment. Furthermore, it was found for the CPe bilayers that the enhanced peaks of the electrostatic potential profiles shift further away from the bilayer center relative to those of PC bilayers. This behavior makes the penetration of cations into the bilayer more difficult and possibly explains the experimentally observed enhanced release rates of anionic compounds in the CPe membrane. Copyright © 2018 Elsevier B.V. All rights reserved.

The role of Caveolin-1 in Lipid Droplets and their Biogenesis

DEFF Research Database (Denmark)

Pezeshkian, Weria; Chevrot, Guillaume; Khandelia, Himanshu

2018-01-01

the effects of a curvature-inducing protein, caveolin-1, on the formation and structure of a spontaneously aggregated triolein (TO) lipid lens in a flat lipid bilayer using Molecular Dynamics (MD) simulations. A truncated form of Caveolin-1 (Cav1) localises on the interface between the spontaneously formed...... TO aggregate and the bulk bilayer, and thins the bilayer at the edge of the aggregate, which may contribute to lowering the energy barrier for pinching off the aggregate from the host bilayer. Simulations of fully mature LDs do not conclusively establish the optimal localisation of Cav1 in LDs, but when Cav1...... is in the LD core, the distribution of both neutral lipids in the LD core, and of phospholipids on the engulfing monolayer are altered significantly. Our simulations provide an unprecedented molecular description of the distribution and dynamics of various lipid species in both mature LDs and in the nascent LD...

1,2-Dielaidoylphosphocholine/1,2-dimyristoylphosphoglycerol supported phospholipid bilayer formation in calcium and calcium-free buffer

International Nuclear Information System (INIS)

Evans, Kervin O.

2012-01-01

Phospholipid membranes are useful in the field of biocatalysis because a supported phospholipid membrane can create a biomimetic platform where biocatalytic processes can readily occur. In this work, supported bilayer formation from sonicated phospholipid vesicles containing 1,2-dielaidoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] was studied using a quartz crystal microbalance with dissipation monitoring and an atomic force microscope. The molar percentages of DEPC and DMPG were varied to determine the effect of overall lipid composition on supported bilayer formation. This work also explored the effect that calcium ion concentration had on supported bilayer formation. Results show that vesicles with up to 50 mol% dimyristoylphosphoglycerol can form a supported bilayer without the presence of calcium ions; however, supported bilayer formation in calcium buffer was inhibited as the anionic (negatively charged) lipid concentration increased. Data suggest that supported phospholipid bilayer formation in the absence of Ca 2+ from vesicles containing negatively charged lipids is specific to phosphatidylglycerol. - Highlights: ► SPB formation of DEPC vesicles containing 0 to 50 mol% DMPG monitored using QCM-D. ► Ca 2+ inhibited SPB formation of DEPC vesicles containing 30 to 50 mol% DMPG. ► Vesicles containing DMPG at 0 to 50 mol% formed SPB in buffer free of Ca 2+ .

Confocal Raman Microscopy for in Situ Measurement of Phospholipid-Water Partitioning into Model Phospholipid Bilayers within Individual Chromatographic Particles.

Science.gov (United States)

Kitt, Jay P; Bryce, David A; Minteer, Shelley D; Harris, Joel M

2018-06-05

The phospholipid-water partition coefficient is a commonly measured parameter that correlates with drug efficacy, small-molecule toxicity, and accumulation of molecules in biological systems in the environment. Despite the utility of this parameter, methods for measuring phospholipid-water partition coefficients are limited. This is due to the difficulty of making quantitative measurements in vesicle membranes or supported phospholipid bilayers, both of which are small-volume phases that challenge the sensitivity of many analytical techniques. In this work, we employ in situ confocal Raman microscopy to probe the partitioning of a model membrane-active compound, 2-(4-isobutylphenyl) propionic acid or ibuprofen, into both hybrid- and supported-phospholipid bilayers deposited on the pore walls of individual chromatographic particles. The large surface-area-to-volume ratio of chromatographic silica allows interrogation of a significant lipid bilayer area within a very small volume. The local phospholipid concentration within a confocal probe volume inside the particle can be as high as 0.5 M, which overcomes the sensitivity limitations of making measurements in the limited membrane areas of single vesicles or planar supported bilayers. Quantitative determination of ibuprofen partitioning is achieved by using the phospholipid acyl-chains of the within-particle bilayer as an internal standard. This approach is tested for measurements of pH-dependent partitioning of ibuprofen into both hybrid-lipid and supported-lipid bilayers within silica particles, and the results are compared with octanol-water partitioning and with partitioning into individual optically trapped phospholipid vesicle membranes. Additionally, the impact of ibuprofen partitioning on bilayer structure is evaluated for both within-particle model membranes and compared with the structural impacts of partitioning into vesicle lipid bilayers.

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

Science.gov (United States)

Wu, Heng-Liang; Tong, Yujin; Peng, Qiling; Li, Na; Ye, Shen

2016-01-21

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

Non-bilayer structures in mitochondrial membranes regulate ATP synthase activity.

Science.gov (United States)

Gasanov, Sardar E; Kim, Aleksandr A; Yaguzhinsky, Lev S; Dagda, Ruben K

2018-02-01

Cardiolipin (CL) is an anionic phospholipid at the inner mitochondrial membrane (IMM) that facilitates the formation of transient non-bilayer (non-lamellar) structures to maintain mitochondrial integrity. CL modulates mitochondrial functions including ATP synthesis. However, the biophysical mechanisms by which CL generates non-lamellar structures and the extent to which these structures contribute to ATP synthesis remain unknown. We hypothesized that CL and ATP synthase facilitate the formation of non-bilayer structures at the IMM to stimulate ATP synthesis. By using 1 H NMR and 31 P NMR techniques, we observed that increasing the temperature (8°C to 37°C), lowering the pH (3.0), or incubating intact mitochondria with CTII - an IMM-targeted toxin that increases the formation of immobilized non-bilayer structures - elevated the formation of non-bilayer structures to stimulate ATP synthesis. The F 0 sector of the ATP synthase complex can facilitate the formation of non-bilayer structures as incubating model membranes enriched with IMM-specific phospholipids with exogenous DCCD-binding protein of the F 0 sector (DCCD-BPF) elevated the formation of immobilized non-bilayer structures to a similar manner as CTII. Native PAGE assays revealed that CL, but not other anionic phospholipids, specifically binds to DCCD-BPF to promote the formation of stable lipid-protein complexes. Mechanistically, molecular docking studies identified two lipid binding sites for CL in DCCD-BPF. We propose a new model of ATP synthase regulation in which CL mediates the formation of non-bilayer structures that serve to cluster protons and ATP synthase complexes as a mechanism to enhance proton translocation to the F 0 sector, and thereby increase ATP synthesis. Copyright © 2017 Elsevier B.V. All rights reserved.

Understanding crumpling lipid vesicles at the gel phase transition

Science.gov (United States)

Hirst, Linda; Ossowski, Adam; Fraser, Matthew

2011-03-01

Wrinkling and crumpling transitions in different membrane types have been studied extensively in recent years both theoretically and computationally. There has also been very interesting recent work on defects in liquid crystalline shells. Lipid bilayer vesicles, widely used in biophysical research can be considered as a single layer smectic shell in the liquid crystalline phase. On cooling the lipid vesicle a transition to the gel phase may take place in which the lipid chains tilt and assume a more ordered packing arrangement. We observe large scale morphological changes in vesicles close to this transition point using fluorescence microscopy and investigate the possible mechanisms for this transition. Confocal microscopy is used to map 3D vesicle shape and crumpling length-scales. We also employ the molecular tilt sensitive dye, Laurdan to investigate the role of tilt domain formation on macroscopic structure. Funded by NSF CAREER award (DMR - BMAT #0852791).

Requirement of transmembrane domain for CD154 association to lipid rafts and subsequent biological events.

Directory of Open Access Journals (Sweden)

Nadir Benslimane

Full Text Available Interaction of CD40 with CD154 leads to recruitment of both molecules into lipid rafts, resulting in bi-directional cell activation. The precise mechanism by which CD154 is translocated into lipid rafts and its impact on CD154 signaling remain largely unknown. Our aim is to identify the domain of CD154 facilitating its association to lipid rafts and the impact of such association on signaling events and cytokine production. Thus, we generated Jurkat cell lines expressing truncated CD154 lacking the cytoplasmic domain or chimeric CD154 in which the transmembrane domain was replaced by that of transferrin receptor I, known to be excluded from lipid rafts. Our results show that cell stimulation with soluble CD40 leads to the association of CD154 wild-type and CD154-truncated, but not CD154-chimera, with lipid rafts. This is correlated with failure of CD154-chimera to activate Akt and p38 MAP kinases, known effectors of CD154 signaling. We also found that CD154-chimera lost the ability to promote IL-2 production upon T cell stimulation with anti-CD3/CD28 and soluble CD40. These results demonstrate the implication of the transmembrane domain of CD154 in lipid raft association, and that this association is necessary for CD154-mediated Akt and p38 activation with consequent enhancement of IL-2 production.

Lipid somersaults

DEFF Research Database (Denmark)

Günther-Pomorski, Thomas; Menon, Anant K.

2016-01-01

Membrane lipids diffuse rapidly in the plane of the membrane but their ability to flip spontaneously across a membrane bilayer is hampered by a significant energy barrier. Thus spontaneous flip-flop of polar lipids across membranes is very slow, even though it must occur rapidly to support diverse...... aspects of cellular life. Here we discuss the mechanisms by which rapid flip-flop occurs, and what role lipid flipping plays in membrane homeostasis and cell growth. We focus on conceptual aspects, highlighting mechanistic insights from biochemical and in silico experiments, and the recent, ground......-breaking identification of a number of lipid scramblases....

Effect of Ring Size in ω-Alicyclic Fatty Acids on the Structural and Dynamical Properties Associated with Fluidity in Lipid Bilayers.

Science.gov (United States)

Poger, David; Mark, Alan E

2015-10-27

Fatty acids containing a terminal cyclic group such as cyclohexyl and cycloheptyl are commonly found in prokaryotic membranes, especially in those of thermo-acidophilic bacteria. These so-called ω-alicyclic fatty acids have been proposed to stabilize the membranes of bacteria by reducing the fluidity in membranes and increasing lipid packing and lipid chain order. In this article, molecular dynamics simulations are used to examine the effect of 3- to 7-membered cycloalkyl saturated and unsaturated (cyclopent-2-enyl and phenyl) rings in ω-alicyclic fatty acyl chains on the structure (lipid packing, lipid chain order, and fraction of gauche defects in the chains) and dynamics (lateral lipid diffusion) of a model lipid bilayer. It was found that ω-alicyclic chains in which the ring was saturated reduced lipid condensation and lowered chain order which would be associated with enhanced fluidity. However, this effect was limited. The lateral diffusion of the lipids diminished as the ring size increased. In particular, ω-cyclohexyl and ω-cycloheptyl acyl tails led to a decrease in lipid diffusion. In contrast, ω-alicyclic acyl chains that contain an unsaturated ring promoted membrane fluidity both in terms of changes in membrane structure and lipid diffusion. This may indicate that saturated and unsaturated terminal rings in ω-alicyclic fatty acids fulfill alternative functions within membranes. Overall, the simulations suggest that ω-alicyclic fatty acids in which the terminal ring is saturated might protect the membrane of thermo-acidophilic bacteria from high-temperature and low-pH conditions through a "dynamical barrier" that would limit lipid diffusion and transmembrane diffusion of undesired ions and molecules.

Quantitative Raman microspectroscopy for water permeability parameters at a droplet interface bilayer.

Science.gov (United States)

Braziel, S; Sullivan, K; Lee, S

2018-01-29

Using confocal Raman microspectroscopy, we derive parameters for bilayer water transport across an isolated nanoliter aqueous droplet pair. For a bilayer formed with two osmotically imbalanced and adherent nanoliter aqueous droplets in a surrounding oil solvent, a droplet interface bilayer (DIB), the water permeability coefficient across the lipid bilayer was determined from monitoring the Raman scattering from the C[triple bond, length as m-dash]N stretching mode of K 3 Fe(CN) 6 as a measure of water uptake into the swelling droplet of a DIB pair. We also derive passive diffusional permeability coefficient for D 2 O transport across a droplet bilayer using O-D Raman signal. This method provides a significant methodological advance in determining water permeability coefficients in a convenient and reliable way.

Monitoring the Orientational Changes of Alamethicin during Incorporation into Bilayer Lipid Membranes.

Science.gov (United States)

Forbrig, Enrico; Staffa, Jana K; Salewski, Johannes; Mroginski, Maria Andrea; Hildebrandt, Peter; Kozuch, Jacek

2018-02-13

Antimicrobial peptides (AMPs) are the first line of defense after contact of an infectious invader, for example, bacterium or virus, with a host and an integral part of the innate immune system of humans. Their broad spectrum of biological functions ranges from cell membrane disruption over facilitation of chemotaxis to interaction with membrane-bound or intracellular receptors, thus providing novel strategies to overcome bacterial resistances. Especially, the clarification of the mechanisms and dynamics of AMP incorporation into bacterial membranes is of high interest, and different mechanistic models are still under discussion. In this work, we studied the incorporation of the peptaibol alamethicin (ALM) into tethered bilayer lipid membranes on electrodes in combination with surface-enhanced infrared absorption (SEIRA) spectroscopy. This approach allows monitoring the spontaneous and potential-induced ion channel formation of ALM in situ. The complex incorporation kinetics revealed a multistep mechanism that points to peptide-peptide interactions prior to penetrating the membrane and adopting the transmembrane configuration. On the basis of the anisotropy of the backbone amide I and II infrared absorptions determined by density functional theory calculations, we employed a mathematical model to evaluate ALM reorientations monitored by SEIRA spectroscopy. Accordingly, ALM was found to adopt inclination angles of ca. 69°-78° and 21° in its interfacially adsorbed and transmembrane incorporated states, respectively. These orientations can be stabilized efficiently by the dipolar interaction with lipid head groups or by the application of a potential gradient. The presented potential-controlled mechanistic study suggests an N-terminal integration of ALM into membranes as monomers or parallel oligomers to form ion channels composed of parallel-oriented helices, whereas antiparallel oligomers are barred from intrusion.

Salt Bridge Formation between the I-BAR Domain and Lipids Increases Lipid Density and Membrane Curvature.

Science.gov (United States)

Takemura, Kazuhiro; Hanawa-Suetsugu, Kyoko; Suetsugu, Shiro; Kitao, Akio

2017-07-28

The BAR domain superfamily proteins sense or induce curvature in membranes. The inverse-BAR domain (I-BAR) is a BAR domain that forms a straight "zeppelin-shaped" dimer. The mechanisms by which IRSp53 I-BAR binds to and deforms a lipid membrane are investigated here by all-atom molecular dynamics simulation (MD), binding energy analysis, and the effects of mutation experiments on filopodia on HeLa cells. I-BAR adopts a curved structure when crystallized, but adopts a flatter shape in MD. The binding of I-BAR to membrane was stabilized by ~30 salt bridges, consistent with experiments showing that point mutations of the interface residues have little effect on the binding affinity whereas multiple mutations have considerable effect. Salt bridge formation increases the local density of lipids and deforms the membrane into a concave shape. In addition, the point mutations that break key intra-molecular salt bridges within I-BAR reduce the binding affinity; this was confirmed by expressing these mutants in HeLa cells and observing their effects. The results indicate that the stiffness of I-BAR is important for membrane deformation, although I-BAR does not act as a completely rigid template.

Micro- and nanofabrication methods for ion channel reconstitution in bilayer lipid membranes

Science.gov (United States)

Tadaki, Daisuke; Yamaura, Daichi; Arata, Kohei; Ohori, Takeshi; Ma, Teng; Yamamoto, Hideaki; Niwano, Michio; Hirano-Iwata, Ayumi

2018-03-01

The self-assembled bilayer lipid membrane (BLM) forms the basic structure of the cell membrane and serves as a major barrier against ion movement. Ion channel proteins function as gated pores that permit ion permeation across the BLM. The reconstitution of ion channel proteins in artificially formed BLMs represents a well-defined system for investigating channel functions and screening drug effects on ion channels. In this review, we will discuss our recent microfabrication approaches to the formation of stable BLMs containing ion channel proteins as a potential platform for next-generation drug screening systems. BLMs formed in a microaperture having a tapered edge exhibited highly stable properties, such as a lifetime of ∼65 h and tolerance to solution changes even after the incorporation of the human ether-a-go-go-related gene (hERG) channel. We also explore a new method of efficiently incorporating human ion channels into BLMs by centrifugation. Our approaches to the formation of stable BLMs and efficient channel incorporation markedly improve the experimental efficiency of BLM reconstitution systems, leading to the realization of a BLM-based high-throughput platform for functional assays of various ion channels.

Exchange bias in diluted-antiferromagnet/antiferromagnet bilayers

International Nuclear Information System (INIS)

Mao, Zhongquan; Zhan, Xiaozhi; Chen, Xi

2015-01-01

The hysteresis-loop properties of a diluted-antiferromagnetic (DAF) layer exchange coupling to an antiferromagnetic (AF) layer are investigated by means of numerical simulations. Remarkable loop shift and coercivity enhancement are observed in such DAF/AF bilayers, while they are absent in the uncoupled DAF single layer. The influences of pinned domains, dilution, cooling field and DAF layer thickness on the loop shift are investigated systematically. The result unambiguously confirms an exchange bias (EB) effect in the DAF/AF bilayers. It also reveals that the EB effect originates from the pinned AF domains within the DAF layer. In contrast to conventional EB systems, frozen uncompensated spins are not found at the interface of the AF pinning layer. (paper)

On ripples and rafts: Curvature induced nanoscale structures in lipid membranes

International Nuclear Information System (INIS)

Schmid, Friederike; Dolezel, Stefan; Meinhardt, Sebastian; Lenz, Olaf

2014-01-01

We develop an elastic theory that predicts the spontaneous formation of nanoscale structures in lipid bilayers which locally phase separate between two phases with different spontaneous monolayer curvature. The theory rationalizes in a unified manner the observation of a variety of nanoscale structures in lipid membranes: Rippled states in one-component membranes, lipid rafts in multicomponent membranes. Furthermore, we report on recent observations of rippled states and rafts in simulations of a simple coarse-grained model for lipid bilayers, which are compatible with experimental observations and with our elastic model

Properties of Fiber Cell Plasma Membranes Isolated from the Cortex and Nucleus of the Porcine Eye Lens

Science.gov (United States)

Mainali, Laxman; Raguz, Marija; O’Brien, William J.; Subczynski, Witold K.

2012-01-01

The organization and physical properties of the lipid bilayer portion of intact cortical and nuclear fiber cell plasma membranes isolated from the eyes lenses of two-year-old pigs were studied using electron paramagnetic resonance (EPR) spin-labeling. Membrane fluidity, hydrophobicity, and the oxygen transport parameter (OTP) were assessed from the EPR spectra of precisely positioned spin labels. Intact cortical and nuclear membranes, which include membrane proteins, were found to contain three distinct lipid environments. These lipid environments were termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain (lipids in protein aggregates). The amount of boundary and trapped lipids was greater in intact nuclear membranes than in cortical membranes. The properties of intact membranes were compared with the organization and properties of lens lipid membranes made of the total lipid extracts from the lens cortex or nucleus. In cortical lens lipid membranes, only one homogenous environment was detected, which was designated as a bulk lipid domain (phospholipid bilayer saturated with cholesterol). Lens lipid membranes prepared from the lens nucleus possessed two domains, assigned as a bulk lipid domain and a cholesterol bilayer domain (CBD). In intact nuclear membranes, it was difficult to discriminate the CBD, which was clearly detected in nuclear lens lipid membranes because the OTP measured in the CBD is the same as in the domain formed by trapped lipids. The two domains unique to intact membranes—namely, the domain formed by boundary lipids and the domain formed by trapped lipids—were most likely formed due to the presence of membrane proteins. It is concluded that formation of rigid and practically impermeable domains is enhanced in the lens nucleus, indicating changes in membrane composition that may help to maintain low oxygen concentration in this lens region. PMID:22326289

Interaction of PLGA and trimethyl chitosan modified PLGA nanoparticles with mixed anionic/zwitterionic phospholipid bilayers studied using molecular dynamics simulations

Science.gov (United States)

Novak, Brian; Astete, Carlos; Sabliov, Cristina; Moldovan, Dorel

2012-02-01

Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable polymer. Nanoparticles of PLGA are commonly used for drug delivery applications. The interaction of the nanoparticles with the cell membrane may influence the rate of their uptake by cells. Both PLGA and cell membranes are negatively charged, so adding positively charged polymers such as trimethyl chitosan (TMC) which adheres to the PLGA particles improves their cellular uptake. The interaction of 3 nm PLGA and TMC-modified-PLGA nanoparticles with lipid bilayers composed of mixtures of phosphatidylcholine and phosphatidylserine lipids was studied using molecular dynamics simulations. The free energy profiles as function of nanoparticles position along the normal direction to the bilayers were calculated, the distribution of phosphatidylserine lipids as a function of distance of the particle from the bilayer was calculated, and the time scale for particle motion in the directions parallel to the bilayer surface was estimated.

The Permeability Enhancing Mechanism of DMSO in Ceramide Bilayers Simulated by Molecular Dynamics

Science.gov (United States)

Notman, Rebecca; den Otter, Wouter K.; Noro, Massimo G.; Briels, W. J.; Anwar, Jamshed

2007-01-01

The lipids of the topmost layer of the skin, the stratum corneum, represent the primary barrier to molecules penetrating the skin. One approach to overcoming this barrier for the purpose of delivery of active molecules into or via the skin is to employ chemical permeability enhancers, such as dimethylsulfoxide (DMSO). How these molecules exert their effect at the molecular level is not understood. We have investigated the interaction of DMSO with gel-phase bilayers of ceramide 2, the predominant lipid in the stratum corneum, by means of molecular dynamics simulations. The simulations satisfactorily reproduce the phase behavior and the known structural parameters of ceramide 2 bilayers in water. The effect of DMSO on the gel-phase bilayers was investigated at various concentrations over the range 0.0−0.6 mol fraction DMSO. The DMSO molecules accumulate in the headgroup region and weaken the lateral forces between the ceramides. At high concentrations of DMSO (≥0.4 mol fraction), the ceramide bilayers undergo a phase transition from the gel phase to the liquid crystalline phase. The liquid-crystalline phase of ceramides is expected to be markedly more permeable to solutes than the gel phase. The results are consistent with the experimental evidence that high concentrations of DMSO fluidize the stratum corneum lipids and enhance permeability. PMID:17513383

Green proteorhodopsin reconstituted into nanoscale phospholipid bilayers (nanodiscs) as photoactive monomers.

Science.gov (United States)

Ranaghan, Matthew J; Schwall, Christine T; Alder, Nathan N; Birge, Robert R

2011-11-16

Over 4000 putative proteorhodopsins (PRs) have been identified throughout the oceans and seas of the Earth. The first of these eubacterial rhodopsins was discovered in 2000 and has expanded the family of microbial proton pumps to all three domains of life. With photophysical properties similar to those of bacteriorhodopsin, an archaeal proton pump, PRs are also generating interest for their potential use in various photonic applications. We perform here the first reconstitution of the minimal photoactive PR structure into nanoscale phospholipid bilayers (nanodiscs) to better understand how protein-protein and protein-lipid interactions influence the photophysical properties of PR. Spectral (steady-state and time-resolved UV-visible spectroscopy) and physical (size-exclusion chromatography and electron microscopy) characterization of these complexes confirms the preparation of a photoactive PR monomer within nanodiscs. Specifically, when embedded within a nanodisc, monomeric PR exhibits a titratable pK(a) (6.5-7.1) and photocycle lifetime (∼100-200 ms) that are comparable to the detergent-solubilized protein. These ndPRs also produce a photoactive blue-shifted absorbance, centered at 377 or 416 nm, that indicates that protein-protein interactions from a PR oligomer are required for a fast photocycle. Moreover, we demonstrate how these model membrane systems allow modulation of the PR photocycle by variation of the discoidal diameter (i.e., 10 or 12 nm), bilayer thickness (i.e., 23 or 26.5 Å), and degree of saturation of the lipid acyl chain. Nanodiscs also offer a highly stable environment of relevance to potential device applications.

Functional Implications of Domain Organization Within Prokaryotic Rhomboid Proteases.

Science.gov (United States)

Panigrahi, Rashmi; Lemieux, M Joanne

2015-01-01

Intramembrane proteases are membrane embedded enzymes that cleave transmembrane substrates. This interesting class of enzyme and its water mediated substrate cleavage mechanism occurring within the hydrophobic lipid bilayer has drawn the attention of researchers. Rhomboids are a family of ubiquitous serine intramembrane proteases. Bacterial forms of rhomboid proteases are mainly composed of six transmembrane helices that are preceded by a soluble N-terminal domain. Several crystal structures of the membrane domain of the E. coli rhomboid protease ecGlpG have been solved. Independently, the ecGlpG N-terminal cytoplasmic domain structure was solved using both NMR and protein crystallography. Despite these structures, we still do not know the structure of the full-length protein, nor do we know the functional role of these domains in the cell. This chapter will review the structural and functional roles of the different domains associated with prokaryotic rhomboid proteases. Lastly, we will address questions remaining in the field.

Stabilization of functional recombinant cannabinoid receptor CB(2 in detergent micelles and lipid bilayers.

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Krishna Vukoti

Full Text Available Elucidation of the molecular mechanisms of activation of G protein-coupled receptors (GPCRs is among the most challenging tasks for modern membrane biology. For studies by high resolution analytical methods, these integral membrane receptors have to be expressed in large quantities, solubilized from cell membranes and purified in detergent micelles, which may result in a severe destabilization and a loss of function. Here, we report insights into differential effects of detergents, lipids and cannabinoid ligands on stability of the recombinant cannabinoid receptor CB(2, and provide guidelines for preparation and handling of the fully functional receptor suitable for a wide array of downstream applications. While we previously described the expression in Escherichia coli, purification and liposome-reconstitution of multi-milligram quantities of CB(2, here we report an efficient stabilization of the recombinant receptor in micelles - crucial for functional and structural characterization. The effects of detergents, lipids and specific ligands on structural stability of CB(2 were assessed by studying activation of G proteins by the purified receptor reconstituted into liposomes. Functional structure of the ligand binding pocket of the receptor was confirmed by binding of (2H-labeled ligand measured by solid-state NMR. We demonstrate that a concerted action of an anionic cholesterol derivative, cholesteryl hemisuccinate (CHS and high affinity cannabinoid ligands CP-55,940 or SR-144,528 are required for efficient stabilization of the functional fold of CB(2 in dodecyl maltoside (DDM/CHAPS detergent solutions. Similar to CHS, the negatively charged phospholipids with the serine headgroup (PS exerted significant stabilizing effects in micelles while uncharged phospholipids were not effective. The purified CB(2 reconstituted into lipid bilayers retained functionality for up to several weeks enabling high resolution structural studies of this GPCR at

Microfluidic passive permeability assay using nanoliter droplet interface lipid bilayers.

Science.gov (United States)

Nisisako, Takasi; Portonovo, Shiva A; Schmidt, Jacob J

2013-11-21

Membrane permeability assays play an important role in assessing drug transport activities across biological membranes. However, in conventional parallel artificial membrane permeability assays (PAMPA), the membrane model used is dissimilar to biological membranes physically and chemically. Here, we describe a microfluidic passive permeability assay using droplet interface bilayers (DIBs). In a microfluidic network, nanoliter-sized donor and acceptor aqueous droplets are alternately formed in cross-flowing oil containing phospholipids. Subsequently, selective removal of oil through hydrophobic pseudo-porous sidewalls induces the contact of the lipid monolayers, creating arrayed planar DIBs between the donor and acceptor droplets. Permeation of fluorescein from the donor to the acceptor droplets was fluorometrically measured. From the measured data and a simple diffusion model we calculated the effective permeabilities of 5.1 × 10(-6) cm s(-1), 60.0 × 10(-6) cm s(-1), and 87.6 × 10(-6) cm s(-1) with donor droplets at pH values of 7.5, 6.4 and 5.4, respectively. The intrinsic permeabilities of specific monoanionic and neutral fluorescein species were obtained similarly. We also measured the permeation of caffeine in 10 min using UV microspectroscopy, obtaining a permeability of 20.8 × 10(-6) cm s(-1). With the small solution volumes, short measurement time, and ability to measure a wide range of compounds, this device has considerable potential as a platform for high-throughput drug permeability assays.

Electronic and Optical Properties of Twisted Bilayer Graphene

Science.gov (United States)

Huang, Shengqiang

The ability to isolate single atomic layers of van der Waals materials has led to renewed interest in the electronic and optical properties of these materials as they can be fundamentally different at the monolayer limit. Moreover, these 2D crystals can be assembled together layer by layer, with controllable sequence and orientation, to form artificial materials that exhibit new features that are not found in monolayers nor bulk. Twisted bilayer graphene is one such prototype system formed by two monolayer graphene layers placed on top of each other with a twist angle between their lattices, whose electronic band structure depends on the twist angle. This thesis presents the efforts to explore the electronic and optical properties of twisted bilayer graphene by Raman spectroscopy and scanning tunneling microscopy measurements. We first synthesize twisted bilayer graphene with various twist angles via chemical vapor deposition. Using a combination of scanning tunneling microscopy and Raman spectroscopy, the twist angles are determined. The strength of the Raman G peak is sensitive to the electronic band structure of twisted bilayer graphene and therefore we use this peak to monitor changes upon doping. Our results demonstrate the ability to modify the electronic and optical properties of twisted bilayer graphene with doping. We also fabricate twisted bilayer graphene by controllable stacking of two graphene monolayers with a dry transfer technique. For twist angles smaller than one degree, many body interactions play an important role. It requires eight electrons per moire unit cell to fill up each band instead of four electrons in the case of a larger twist angle. For twist angles smaller than 0.4 degree, a network of domain walls separating AB and BA stacking regions forms, which are predicted to host topologically protected helical states. Using scanning tunneling microscopy and spectroscopy, these states are confirmed to appear on the domain walls when inversion

Insights into the role of cyclic ladderane lipids in bacteria from computer simulations

DEFF Research Database (Denmark)

Chaban, Vitaly V; Kopec, Wojciech; Nielsen, Morten B

2014-01-01

Ladderanes, which are multiple fused cyclobutane rings, are unique structures available only in nature. Anammox bacteria produce ladderane phospholipids during their life cycle, but the synthesis mechanism still remains a mystery. The function of ladderane lipids in the membrane is unclear as well...... containing ladderane lipids. The structural and thermodynamics differences among (1) pure ladderane containing bilayer, (2) POPC bilayer, and (3) their equimolar mixture are discussed. Potentials of mean force are reported for the translocation of a hydrazine molecule through all investigated bilayers. All...... bilayers offer a potential energy barrier to hydrazine. Contrary to expectations, the presence of the ladderane lipids somewhat lowers the barrier for translocation of hydrazine. We conclude that the presence of ladderane phospholipids in anammox bacteria does not serve as a barrier to hydrazine. It may...

Spontaneous insertion of GPI anchors into cholesterol-rich membrane domains

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Jing Li

2018-05-01

Full Text Available GPI-Anchored proteins (GPI-APs can be exogenously transferred onto bilayer membranes both in vivo and in vitro, while the mechanism by which this transfer process occurs is unknown. In this work, we used atomistic molecular dynamics simulations and free energy calculations to characterize the essential influence of cholesterol on insertion of the GPI anchors into plasma membranes. We demonstrate, both dynamically and energetically, that in the presence of cholesterol, the tails of GPI anchors are able to penetrate inside the core of the lipid membrane spontaneously with a three-step mechanism, while in the absence of cholesterol no spontaneous insertion was observed. We ascribe the failure of insertion to the strong thermal fluctuation of lipid molecules in cholesterol-free bilayer, which generates a repulsive force in entropic origin. In the presence of cholesterol, however, the fluctuation of lipids is strongly reduced, thus decreasing the barrier for the anchor insertion. Based on this observation, we propose a hypothesis that addition of cholesterol creates vertical creases in membranes for the insertion of acyl chains. Moreover, we find that the GPI anchor could also spontaneously inserted into the boundary between cholesterol-rich and cholesterol-depleted domains. Our results shed light on the mechanism of cholesterol-mediated interaction between membrane proteins with acyl chain and plasma membranes in living cells.

Spontaneous insertion of GPI anchors into cholesterol-rich membrane domains

Science.gov (United States)

Li, Jing; Liu, Xiuhua; Tian, Falin; Yue, Tongtao; Zhang, Xianren; Cao, Dapeng

2018-05-01

GPI-Anchored proteins (GPI-APs) can be exogenously transferred onto bilayer membranes both in vivo and in vitro, while the mechanism by which this transfer process occurs is unknown. In this work, we used atomistic molecular dynamics simulations and free energy calculations to characterize the essential influence of cholesterol on insertion of the GPI anchors into plasma membranes. We demonstrate, both dynamically and energetically, that in the presence of cholesterol, the tails of GPI anchors are able to penetrate inside the core of the lipid membrane spontaneously with a three-step mechanism, while in the absence of cholesterol no spontaneous insertion was observed. We ascribe the failure of insertion to the strong thermal fluctuation of lipid molecules in cholesterol-free bilayer, which generates a repulsive force in entropic origin. In the presence of cholesterol, however, the fluctuation of lipids is strongly reduced, thus decreasing the barrier for the anchor insertion. Based on this observation, we propose a hypothesis that addition of cholesterol creates vertical creases in membranes for the insertion of acyl chains. Moreover, we find that the GPI anchor could also spontaneously inserted into the boundary between cholesterol-rich and cholesterol-depleted domains. Our results shed light on the mechanism of cholesterol-mediated interaction between membrane proteins with acyl chain and plasma membranes in living cells.

The structure of a lipid-water lamellar phase containing two types of lipid monolayers

International Nuclear Information System (INIS)

Ranck, J.L.; Luzzati, V.; Zaccai, G.

1980-01-01

One lamellar phase, observed in the mitochondrial lipids-water system at low temperature (ca 253 K) and at low water content (ca 15%), contains four lipid monolayers in its unit cell, two of type α and two of type β. Previous X-ray scattering studies of this phase led to an ambiguity: the phase could contain either two homogeneous bilayers, one α and one β, or two mixed bilayers, each formed by an α and a β monolayer. A solution to this problem was sought in a neutron scattering study as a function of the D 2 O/H 2 O ratio. Because of limited resolution, straightforward analysis of the neutron scattering data leads also to ambiguous results. Using a more sophisticated analysis based upon the zeroth- and second-order moments of the Patterson peaks relevant to the exchangeable components, it is shown that the weight of the evidence is in favour of a structure containing mixed bilayers. (Auth.)

Reorganization of plasma membrane lipid domains during conidial germination.

Science.gov (United States)

Santos, Filipa C; Fernandes, Andreia S; Antunes, Catarina A C; Moreira, Filipe P; Videira, Arnaldo; Marinho, H Susana; de Almeida, Rodrigo F M

2017-02-01

Neurospora crassa, a filamentous fungus, in the unicellular conidial stage has ideal features to study sphingolipid (SL)-enriched domains, which are implicated in fundamental cellular processes ranging from antifungal resistance to apoptosis. Several changes in lipid metabolism and in the membrane composition of N. crassa occur during spore germination. However, the biophysical impact of those changes is unknown. Thus, a biophysical study of N. crassa plasma membrane, particularly SL-enriched domains, and their dynamics along conidial germination is prompted. Two N. crassa strains, wild-type (WT) and slime, which is devoid of cell wall, were studied. Conidial growth of N. crassa WT from a dormancy state to an exponential phase was accompanied by membrane reorganization, namely an increase of membrane fluidity, occurring faster in a supplemented medium than in Vogel's minimal medium. Gel-like domains, likely enriched in SLs, were found in both N. crassa strains, but were particularly compact, rigid and abundant in the case of slime cells, even more than in budding yeast Saccharomyces cerevisiae. In N. crassa, our results suggest that the melting of SL-enriched domains occurs near growth temperature (30°C) for WT, but at higher temperatures for slime. Regarding biophysical properties strongly affected by ergosterol, the plasma membrane of slime conidia lays in between those of N. crassa WT and S. cerevisiae cells. The differences in biophysical properties found in this work, and the relationships established between membrane lipid composition and dynamics, give new insights about the plasma membrane organization and structure of N. crassa strains during conidial growth. Copyright © 2016 Elsevier B.V. All rights reserved.

Dependency of {gamma}-secretase complex activity on the structural integrity of the bilayer

Energy Technology Data Exchange (ETDEWEB)

Zhou, Hua, E-mail: hzhou2@lbl.gov [Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 (United States); Zhou, Shuxia; Walian, Peter J.; Jap, Bing K. [Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 (United States)

2010-11-12

Research highlights: {yields} Partial solubilization of membranes with CHAPSO can increase {gamma}-secretase activity. {yields} Completely solubilized {gamma}-secretase is inactive. {yields} Purified {gamma}-secretase regains activity after reconstitution into lipid bilayers. {yields} A broad range of detergents can be used to successfully reconstitute {gamma}-secretase. -- Abstract: {gamma}-secretase is a membrane protein complex associated with the production of A{beta} peptides that are pathogenic in Alzheimer's disease. We have characterized the activity of {gamma}-secretase complexes under a variety of detergent solubilization and reconstitution conditions, and the structural state of proteoliposomes by electron microscopy. We found that {gamma}-secretase activity is highly dependent on the physical state or integrity of the membrane bilayer - partial solubilization may increase activity while complete solubilization will abolish it. The activity of well-solubilized {gamma}-secretase can be restored to near native levels when properly reconstituted into a lipid bilayer environment.

Diffusion studies on permeable nitroxyl spin probes through bilayer lipid membranes: A low frequency ESR study

International Nuclear Information System (INIS)

Meenakumari, V.; Benial, A. Milton Franklin; Utsumi, Hideo; Ichikawa, Kazuhiro; Yamada, Ken-ichi; Hyodo, Fuminori; Jawahar, A.

2015-01-01

Electron spin resonance (ESR) studies were carried out for permeable 2mM 14 N-labeled deutrated 3 Methoxy carbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL) in pure water and 1mM, 2mM, 3mM, 4mM concentration of 14N-labeled deutrated MC-PROXYL in 400mM concentration of liposomal solution by using a 300 MHz ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, partition parameter and permeability were reported for these samples. The line broadening was observed for the nitroxyl spin probe in the liposomal solution. The line broadening indicates that the high viscous nature of the liposomal solution. The partition parameter and permeability values indicate the maximum diffusion of nitroxyl spin probes in the bilayer lipid membranes at 2 mM concentration of nitroxyl radical. This study illustrates that ESR can be used to differentiate between the intra and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe. From the ESR results, the spin probe concentration was optimized as 2mM in liposomal solution for ESR phantom studies/imaging, invivo and invitro experiments

Randomly organized lipids and marginally stable proteins: a coupling of weak interactions to optimize membrane signaling.

Science.gov (United States)

Rice, Anne M; Mahling, Ryan; Fealey, Michael E; Rannikko, Anika; Dunleavy, Katie; Hendrickson, Troy; Lohese, K Jean; Kruggel, Spencer; Heiling, Hillary; Harren, Daniel; Sutton, R Bryan; Pastor, John; Hinderliter, Anne

2014-09-01

Eukaryotic lipids in a bilayer are dominated by weak cooperative interactions. These interactions impart highly dynamic and pliable properties to the membrane. C2 domain-containing proteins in the membrane also interact weakly and cooperatively giving rise to a high degree of conformational plasticity. We propose that this feature of weak energetics and plasticity shared by lipids and C2 domain-containing proteins enhance a cell's ability to transduce information across the membrane. We explored this hypothesis using information theory to assess the information storage capacity of model and mast cell membranes, as well as differential scanning calorimetry, carboxyfluorescein release assays, and tryptophan fluorescence to assess protein and membrane stability. The distribution of lipids in mast cell membranes encoded 5.6-5.8bits of information. More information resided in the acyl chains than the head groups and in the inner leaflet of the plasma membrane than the outer leaflet. When the lipid composition and information content of model membranes were varied, the associated C2 domains underwent large changes in stability and denaturation profile. The C2 domain-containing proteins are therefore acutely sensitive to the composition and information content of their associated lipids. Together, these findings suggest that the maximum flow of signaling information through the membrane and into the cell is optimized by the cooperation of near-random distributions of membrane lipids and proteins. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova. Copyright © 2014 Elsevier B.V. All rights reserved.

Vortex dynamics in ferromagnetic/superconducting bilayers

Energy Technology Data Exchange (ETDEWEB)

Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

2008-07-01

The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)

G protein-membrane interactions II: Effect of G protein-linked lipids on membrane structure and G protein-membrane interactions.

Science.gov (United States)

Casas, Jesús; Ibarguren, Maitane; Álvarez, Rafael; Terés, Silvia; Lladó, Victoria; Piotto, Stefano P; Concilio, Simona; Busquets, Xavier; López, David J; Escribá, Pablo V

2017-09-01

G proteins often bear myristoyl, palmitoyl and isoprenyl moieties, which favor their association with the membrane and their accumulation in G Protein Coupled Receptor-rich microdomains. These lipids influence the biophysical properties of membranes and thereby modulate G protein binding to bilayers. In this context, we showed here that geranylgeraniol, but neither myristate nor palmitate, increased the inverted hexagonal (H II ) phase propensity of phosphatidylethanolamine-containing membranes. While myristate and palmitate preferentially associated with phosphatidylcholine membranes, geranylgeraniol favored nonlamellar-prone membranes. In addition, Gαi 1 monomers had a higher affinity for lamellar phases, while Gβγ and Gαβγ showed a marked preference for nonlamellar prone membranes. Moreover, geranylgeraniol enhanced the binding of G protein dimers and trimers to phosphatidylethanolamine-containing membranes, yet it decreased that of monomers. By contrast, both myristate and palmitate increased the Gαi 1 preference for lamellar membranes. Palmitoylation reinforced the binding of the monomer to PC membranes and myristoylation decreased its binding to PE-enriched bilayer. Finally, binding of dimers and trimers to lamellar-prone membranes was decreased by palmitate and myristate, but it was increased in nonlamellar-prone bilayers. These results demonstrate that co/post-translational G protein lipid modifications regulate the membrane lipid structure and that they influence the physico-chemical properties of membranes, which in part explains why G protein subunits sort to different plasma membrane domains. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá. Copyright © 2017 Elsevier B.V. All rights reserved.

Lab on a Biomembrane: Rapid prototyping and manipulation of 2D fluidic lipid bilayers circuits

Science.gov (United States)

Ainla, Alar; Gözen, Irep; Hakonen, Bodil; Jesorka, Aldo

2013-01-01

Lipid bilayer membranes are among the most ubiquitous structures in the living world, with intricate structural features and a multitude of biological functions. It is attractive to recreate these structures in the laboratory, as this allows mimicking and studying the properties of biomembranes and their constituents, and to specifically exploit the intrinsic two-dimensional fluidity. Even though diverse strategies for membrane fabrication have been reported, the development of related applications and technologies has been hindered by the unavailability of both versatile and simple methods. Here we report a rapid prototyping technology for two-dimensional fluidic devices, based on in-situ generated circuits of phospholipid films. In this “lab on a molecularly thin membrane”, various chemical and physical operations, such as writing, erasing, functionalization, and molecular transport, can be applied to user-defined regions of a membrane circuit. This concept is an enabling technology for research on molecular membranes and their technological use. PMID:24067786

Filament networks attached to membranes: cytoskeletal pressure and local bilayer deformation

International Nuclear Information System (INIS)

Auth, Thorsten; Safran, S A; Gov, Nir S

2007-01-01

Several cell types, among them red blood cells, have a cortical, two-dimensional (2D) network of filaments sparsely attached to their lipid bilayer. In many mammalian cells, this 2D polymer network is connected to an underlying 3D, more rigid cytoskeleton. In this paper, we consider the pressure exerted by the thermally fluctuating, cortical network of filaments on the bilayer and predict the bilayer deformations that are induced by this pressure. We treat the filaments as flexible polymers and calculate the pressure that a network of such linear chains exerts on the bilayer; we then minimize the bilayer shape in order to predict the resulting local deformations. We compare our predictions with membrane deformations observed in electron micrographs of red blood cells. The polymer pressure along with the resulting membrane deformation can lead to compartmentalization, regulate in-plane diffusion and may influence protein sorting as well as transmit signals to the polymerization of the underlying 3D cytoskeleton

Electroporation-Induced Cell Modifications Detected with THz Time-Domain Spectroscopy

Science.gov (United States)

Romeo, Stefania; Vernier, P. Thomas; Zeni, Olga

2018-04-01

Electroporation (electropermeabilization) increases the electrical conductivity of biological cell membranes and lowers transport barriers for normally impermeant materials. Molecular simulations suggest that electroporation begins with the reorganization of water and lipid head group dipoles in the phospholipid bilayer interface, driven by an externally applied electric field, and the evolution of the resulting defects into water-filled, lipid pores. The interior of the electroporated membrane thus contains water, which should provide a signature for detection of the electropermeabilized state. In this feasibility study, we use THz time-domain spectroscopy, a powerful tool for investigating biomolecular systems and their interactions with water, to detect electroporation in human cells subjected to permeabilizing pulsed electric fields (PEFs). The time-domain response of electroporated human monocytes was acquired with a commercial THz, time-domain spectrometer. For each sample, frequency spectra were calculated, and the absorption coefficient and refractive index were extracted in the frequency range between 0.2 and 1.5 THz. This analysis reveals a higher absorption of THz radiation by PEF-exposed cells, with respect to sham-exposed ones, consistent with the intrusion of water into the cell through the permeabilized membrane that is presumed to be associated with electroporation.

Biosynthesis of archaeal membrane ether lipids

Directory of Open Access Journals (Sweden)

Samta eJain

2014-11-01

Full Text Available A vital function of the cell membrane in all living organism is to maintain the membrane permeability barrier and fluidity. The composition of the phospholipid bilayer is distinct in archaea when compared to bacteria and eukarya. In archaea, isoprenoid hydrocarbon side chains are linked via an ether bond to the sn-glycerol-1-phosphate backbone. In bacteria and eukarya on the other hand, fatty acid side chains are linked via an ester bond to the sn-glycerol-3-phosphate backbone. The polar head groups are globally shared in the three domains of life. The unique membrane lipids of archaea have been implicated not only in the survival and adaptation of the organisms to extreme environments but also to form the basis of the membrane composition of the last universal common ancestor (LUCA. In nature, a diverse range of archaeal lipids is found, the most common are the diether (or archaeol and the tetraether (or caldarchaeol lipids that form a monolayer. Variations in chain length, cyclization and other modifications lead to diversification of these lipids. The biosynthesis of these lipids is not yet well understood however progress in the last decade has led to a comprehensive understanding of the biosynthesis of archaeol. This review describes the current knowledge of the biosynthetic pathway of archaeal ether lipids; insights on the stability and robustness of archaeal lipid membranes; and evolutionary aspects of the lipid divide and the last universal common ancestor LUCA. It examines recent advances made in the field of pathway reconstruction in bacteria.

Imaging of topological magnetic pinning in superconductor-ferrimagnet bilayer with scanning Hall microscopy

International Nuclear Information System (INIS)

Marchevsky, M; Higgins, M J; Bhattacharya, S; Fratello, V J

2011-01-01

In a superconducting film deposited on ferromagnetic substrate with perpendicular magnetic anisotropy, vortex matter is confined by the magnetic potential landscape. Using scanning Hall microscopy we visualize flux accumulation and removal in a superconductor-ferrimagnet (S/F) bilayer prepared by rf sputtering of thin niobium film on bismuth-doped rare-earth iron garnet. Penetration of the perpendicular magnetic field in the S/F bilayer follows magnetic domain boundaries and is laterally guided by the garnet magnetization component along the field direction. Upon field removal, localization of the remnant flux at the disclination points of the labyrinthine domain pattern is observed. Our experiments show evidence for strong vortex pinning due the special topology of the domain pattern. Ac magnetic imaging of the transport current distribution in the bilayer reveals complex flow paths commensurate with the magnetic domain boundaries. Topological magnetic pinning can be a useful tool for enhancement and control of critical current in thin film superconductors.

Imaging of topological magnetic pinning in superconductor-ferrimagnet bilayer with scanning Hall microscopy

Energy Technology Data Exchange (ETDEWEB)

Marchevsky, M [Department of Physics, Syracuse University, Syracuse, NY 12344 (United States); Higgins, M J [Princeton High School, Princeton, NJ 08540 (United States); Bhattacharya, S [Tata Institute of Fundamental Research, Mumbai 400 005 (India); Fratello, V J, E-mail: mmartchevskii@lbl.gov [Integrated Photonics, Inc., Hillsborough, NJ 08844 (United States)

2011-02-15

In a superconducting film deposited on ferromagnetic substrate with perpendicular magnetic anisotropy, vortex matter is confined by the magnetic potential landscape. Using scanning Hall microscopy we visualize flux accumulation and removal in a superconductor-ferrimagnet (S/F) bilayer prepared by rf sputtering of thin niobium film on bismuth-doped rare-earth iron garnet. Penetration of the perpendicular magnetic field in the S/F bilayer follows magnetic domain boundaries and is laterally guided by the garnet magnetization component along the field direction. Upon field removal, localization of the remnant flux at the disclination points of the labyrinthine domain pattern is observed. Our experiments show evidence for strong vortex pinning due the special topology of the domain pattern. Ac magnetic imaging of the transport current distribution in the bilayer reveals complex flow paths commensurate with the magnetic domain boundaries. Topological magnetic pinning can be a useful tool for enhancement and control of critical current in thin film superconductors.

Lipid Structure in Triolein Lipid Droplets

DEFF Research Database (Denmark)

Chaban, Vitaly V; Khandelia, Himanshu

2014-01-01

of a mass of hydrophobic lipid esters coved by phospholipid monolayer. The small size and unique architecture of LDs makes it complicated to study LD structure by modern experimental methods. We discuss coarse-grained molecular dynamics (MD) simulations of LD formation in systems containing 1-palmitoyl-2...... to coarse-grained simulations, the presence of PE lipids at the interface has a little impact on distribution of components and on the overall LD structure. (4) The thickness of the lipid monolayer at the surface of the droplet is similar to the thickness of one leaflet of a bilayer. Computer simulations......Lipid droplets (LDs) are primary repositories of esterified fatty acids and sterols in animal cells. These organelles originate on the lumenal or cytoplasmic side of endoplasmic reticulum (ER) membrane and are released to the cytosol. In contrast to other intracellular organelles, LDs are composed...

Interplay of electrostatics and lipid packing determines the binding of charged polymer coated nanoparticles to model membranes.

Science.gov (United States)

Biswas, Nupur; Bhattacharya, Rupak; Saha, Arindam; Jana, Nikhil R; Basu, Jaydeep K

2015-10-07

Understanding of nanoparticle-membrane interactions is useful for various applications of nanoparticles like drug delivery and imaging. Here we report on the studies of interaction between hydrophilic charged polymer coated semiconductor quantum dot nanoparticles with model lipid membranes. Atomic force microscopy and X-ray reflectivity measurements suggest that cationic nanoparticles bind and penetrate bilayers of zwitterionic lipids. Penetration and binding depend on the extent of lipid packing and result in the disruption of the lipid bilayer accompanied by enhanced lipid diffusion. On the other hand, anionic nanoparticles show minimal membrane binding although, curiously, their interaction leads to reduction in lipid diffusivity. It is suggested that the enhanced binding of cationic QDs at higher lipid packing can be understood in terms of the effective surface potential of the bilayers which is tunable through membrane lipid packing. Our results bring forth the subtle interplay of membrane lipid packing and electrostatics which determine nanoparticle binding and penetration of model membranes with further implications for real cell membranes.

Molecular structure of the lecithin ripple phase

Science.gov (United States)

de Vries, Alex H.; Yefimov, Serge; Mark, Alan E.; Marrink, Siewert J.

2005-04-01

Molecular dynamics simulations of lecithin lipid bilayers in water as they are cooled from the liquid crystalline phase show the spontaneous formation of rippled bilayers. The ripple consists of two domains of different length and orientation, connected by a kink. The organization of the lipids in one domain of the ripple is found to be that of a splayed gel; in the other domain the lipids are gel-like and fully interdigitated. In the concave part of the kink region between the domains the lipids are disordered. The results are consistent with the experimental information available and provide an atomic-level model that may be tested by further experiments. molecular dynamics simulation | structural model

Ion Channels Induced by Antimicrobial Agents in Model Lipid Membranes are Modulated by Plant Polyphenols Through Surrounding Lipid Media.

Science.gov (United States)

Efimova, Svetlana S; Zakharova, Anastasiia A; Medvedev, Roman Ya; Ostroumova, Olga S

2018-03-16

The potential therapeutic applications of plant polyphenols in various neurological, cardiovascular, metabolic and malignant disorders determine the relevance of studying the molecular mechanisms of their action on the cell membranes. Here, the quantitative changes in the physical parameters of model bilayer lipid membranes upon the adsorption of plant polyphenols were evaluated. It was shown that butein and naringenin significantly decreased the intrinsic dipole potential of cholesterol-free and cholesterol-enriched membranes. Cardamonin, 4'-hydroxychalcone, licochalcone A and liquiritigenin demonstrated the average efficiency, while resveratrol did not characterized by the ability to modulate the bilayer electrostatics. At the same time, the tested polyphenols affected melting of phospholipids with saturated acyl chains. The effects were attributed to the lipid disordering and a promotion of the positive curvature stress. According to DSC data and results of measurements of the threshold voltages that cause bilayer breakdown licochalcone A is the most effective agent. Furthermore, the role of the polyphenol induced changes in the electric and elastic properties of lipid host in the regulation of reconstituted ion channels was examined. The ability of the tested polyphenols to decrease the conductance of single ion channels produced by the antifungal cyclic lipopeptide syringomycin E was in agreement with their effects on the dipole potential of the lipid bilayers. The greatest effect of licochalcone A on the steady-state membrane conductance induced by the antifungal polyene macrolide antibiotic nystatin correlated with its greatest efficacy to induce the positive curvature stress. We also found that butein and naringenin bind specifically to a single pore formed by α-hemolysin from Staphylococcus aureus.

Lindane Suppresses the Lipid-bilayer Permeability in Main Transition Region

DEFF Research Database (Denmark)