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At least 163 records · Page 9Linked to original sources
PubMed1991

Iodide penetration into lipid bilayers as a probe of membrane lipid organization.

The quenching efficiency of iodide as a penetrating fluorescence quencher for a membrane-associated fluorophore was utilized to measure the molecular packing of lipid bilayers. The KI quenching efficiency of tryptophan-fluorescence from melittin incorporated in DMPC bilayer vesicles peaks at the phase transition temperature (24 degrees C) of DMPC, whereas acrylamide quenching efficiency does not depend on temperature. The ability of iodide to penetrate the hydrocarbon region of the bilayer was examined by measuring the fluorescence quenching of the pyrene-phosphatidylcholine incorporated into DMPC vesicles (pyrene was attached to the 10th carbon of the sn-2 chain). The quenching efficiency of pyrene by iodide again shows a maximum at the lipid phase transition. We conclude that iodide penetrates the membrane hydrocarbon region at phase transition through an increased number of bilayer defects. The magnitude of change in quenching efficiency of iodide during lipid phase transition provides a sensitive technique to probe the lipid organization in membranes.

Lipid Bilayers↗
PubMed2002

Perfluorooctyl bromide has limited membrane solubility and is located at the bilayer center. Locating small molecules in lipid bilayers through paramagnetic enhancements of NMR relaxation.

There is considerable interest in the use of perfluorocarbons as oxygen carriers in clinical settings; however, little is known regarding the molecular interactions made by these apolar compounds with biological membranes or their effect on membrane structure. NMR spectroscopy was used to investigate the interaction of perfluorooctyl bromide (PFOB) with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers. (19)F NMR spectra demonstrate that PFOB partitions into POPC bilayers but that it saturates at a remarkably low membrane concentration of approximately 2 mol %. (19)F chemical shifts indicate that this membrane-bound PFOB experiences a local environment similar in polarity to that of hexane, suggesting that the compound resides within the hydrocarbon core of the lipid bilayer. This hydrocarbon location was refined by measuring paramagnetic enhancements of (19)F nuclear relaxation for membrane-bound PFOB produced by Gd(3+) and O(2). The data clearly localize PFOB to the center of the membrane hydrocarbon and show how paramagnetic enhancements of nuclear relaxation produced by O(2) may be used to localize small molecules within bilayers. (2)H and (31)P NMR experiments demonstrate that PFOB produces no significant changes in either acyl chain or headgroup structure even at saturating membrane concentrations.

Cell Membrane↗
PubMed2001

Steric effects on interaction of tea catechins with lipid bilayers.

Interaction of tea catechins with lipid bilayers has been investigated with liposome systems. Tea catechins are classified into cis-type and trans-type from the configuration of the two hydrogens at the 2 and 3 positions on the C-ring. The amount of trans-type catechins incorporated into liposomes was less than that of the respective cis-type catechins. Furthermore, the order of the partition coefficients of catechins in an n-octanol/PBS system is the same as that of the amount incorporated into liposomes. These results indicate that in addition to the number of hydroxyl groups on the B-ring and the presence of the galloyl moiety, the stereochemical structure of the C-ring also governs the hydrophobicity and the affinity for lipid bilayers. Trans-type catechins with the galloyl moiety were located on the surface of the lipid bilayer, as well as cis-type catechins with the galloyl moiety, and perturbed the membrane structure. These different stereochemical structures should influence the affinity for lipid bilayers, the alteration of membrane structures, and the difference in the order of the biological activities.

Catechin↗
PubMed2006

Formation of solid-supported lipid bilayers: an integrated view.

Supported lipid bilayers (SLBs) are popular models of cell membranes with potential bio-technological applications. A qualitative understanding of the process of SLB formation after exposure of small lipid vesicles to a hydrophilic support is now emerging. Recent studies have revealed a stunning variety of effects that can take place during this self-organization process. The ensemble of results in our group has revealed unprecedented insight into intermediates of the SLB-formation process and has helped to identify a number of parameters that are determinant for the lipid deposition on solid supports. The pathway of lipid deposition can be tuned by electrostatic interactions and by the presence of calcium. We emphasize the importance of the solid support in the SLB-formation process. Our results suggest that the molecular-level interaction between lipids and the solid support needs to be considered explicitly, to understand the rupture of vesicles and the formation of SLBs as well as to predict the properties of the resulting SLB. The impact of the SLB-formation process on the quality and the physical properties of the resulting SLB as well as implications for other types of surface-confined lipid bilayers are discussed.

Adsorption↗
PubMed2004

Cationic DMPC/DMTAP lipid bilayers: molecular dynamics study.

Cationic lipid membranes are known to form compact complexes with DNA and to be effective as gene delivery agents both in vitro and in vivo. Here we employ molecular dynamics simulations for a detailed atomistic study of lipid bilayers consisting of a mixture of cationic dimyristoyltrimethylammonium propane (DMTAP) and zwitterionic dimyristoylphosphatidylcholine (DMPC). Our main objective is to examine how the composition of the DMPC/DMTAP bilayers affects their structural and electrostatic properties in the liquid-crystalline phase. By varying the mole fraction of DMTAP, we have found that the area per lipid has a pronounced nonmonotonic dependence on the DMTAP concentration, with a minimum around the point of equimolar DMPC/DMTAP mixture. We show that this behavior has an electrostatic origin and is driven by the interplay between positively charged TAP headgroups and the zwitterionic phosphatidylcholine (PC) heads. This interplay leads to considerable reorientation of PC headgroups for an increasing DMTAP concentration, and gives rise to major changes in the electrostatic properties of the lipid bilayer, including a significant increase of total dipole potential across the bilayer and prominent changes in the ordering of water in the vicinity of the membrane. Moreover, chloride counterions are bound mostly to PC nitrogens implying stronger screening of PC heads by Cl ions compared to TAP headgroups. The implications of these findings are briefly discussed.

Computer Simulation↗
PubMedDate not supplied

[Properties of bilayer lipid membranes formed from cholesterol and alkyltrimethylammonium bromides].

Flat bilayer lipid membranes (BLM) were obtained from cholesterol solution in n-octane in the presence of detergents of alkyltrimethyl ammonium bromides series in water medium. It has been shown that highly stable BLM are obtained only for the detergents of this series with the alkyl chain higher than C12. Changes in stability and electromechanical strength of the latter are conditioned by the peculiarities of stechiometric interaction between the molecules of cholesterol, detergent and solvent in the lipid bilayer.

Bromides↗
PubMed2000

Tethered polymer-supported planar lipid bilayers for reconstitution of integral membrane proteins: silane-polyethyleneglycol-lipid as a cushion and covalent linker.

There is increasing interest in supported membranes as models of biological membranes and as a physiological matrix for studying the structure and function of membrane proteins and receptors. A common problem of protein-lipid bilayers that are directly supported on a hydrophilic substrate is nonphysiological interactions of integral membrane proteins with the solid support to the extent that they will not diffuse in the plane of the membrane. To alleviate some of these problems we have developed a new tethered polymer-supported planar lipid bilayer system, which permitted us to reconstitute integral membrane proteins in a laterally mobile form. We have supported lipid bilayers on a newly designed polyethyleneglycol cushion, which provided a soft support and, for increased stability, covalent linkage of the membranes to the supporting quartz or glass substrates. The formation and morphology of the bilayers were followed by total internal reflection and epifluorescence microscopy, and the lateral diffusion of the lipids and proteins in the bilayer was monitored by fluorescence recovery after photobleaching. Uniform bilayers with high lateral lipid diffusion coefficients (0.8-1.2 x 10(-8) cm(2)/s) were observed when the polymer concentration was kept slightly below the mushroom-to-brush transition. Cytochrome b(5) and annexin V were used as first test proteins in this system. When reconstituted in supported bilayers that were directly supported on quartz, both proteins were largely immobile with mobile fractions < 25%. However, two populations of laterally mobile proteins were observed in the polymer-supported bilayers. Approximately 25% of cytochrome b(5) diffused with a diffusion coefficient of approximately 1 x 10(-8) cm(2)/s, and 50-60% diffused with a diffusion coefficient of approximately 2 x 10(-10) cm(2)/s. Similarly, one-third of annexin V diffused with a diffusion coefficient of approximately 3 x 10(-9) cm(2)/s, and two-thirds diffused with a diffusion coefficient of approximately 4 x 10(-10) cm(2)/s. A model for the interaction of these proteins with the underlying polymer is discussed.

Annexin A5↗
PubMedDate not supplied

Facile functionalization of lipid bilayer vesicles by titania: the use of cerasome-forming lipids for surface and core modification.

Two kinds of functionalization of a lipid bilayer vesicle by titania were achieved by utilizing a cerasome-forming lipid, which is the starting material to prepare a cerasome, a morphologically stable lipid bilayer vesicle having an atomic layer of siloxane networks on its surface. One system is the preparation of the titania-coated cerasomes by immobilizing nanaometer-sizes of titania onto the surface siloxane network of cerasomes. The other is the creation of an asymmetric lipid bilayer structure on the surface of the colloidal titania particles. The characteristics of these surface- and core-functionalized vesicles were investigated, and it was found that these conjugates showed photocatalytic activity as evaluated by photolysis experiments of the cationic dye methylene blue.

Catalysis↗
PubMed1999

Oxidation-dependent changes in the stability and permeability of lipid bilayers.

Peroxidation-dependent change in the permeability of lipid bilayers was mesaured by using artificial membrane systems, that is, planar lipid bilayers and liposomes. The unsaturated fatty acyl chains of phospholipids in small unilamellar vesicles were peroxidized time-dependently by the hydroxyl radical chemically generated by the reaction of H2O2 and Cu(en)2. In contrast, at the same hydroxyl radical concentration and time ranges, no ionic current through the planar lipid bilayers and no release of K+ from the liposomes were observed. These findings indicate that accumulation of lipid peroxide within lipid bilayers is not responsible for the permeability increase that is often observed in biomembranes exposed to oxidative stresses. Higher concentration of the hydroxyl radical caused break-down of the planar lipid bilayers composed of the mixture (7:3) of phosphatidylethanolamine (PE) and phosphatidylcholine (PC). The bilayer containing 100% PE at least at one leaflet of the bilayer (facing the hydroxyl radical-generating solution) was not broken-down by the application of the hydroxyl radical, suggesting that PE stabilizes the planar lipid bilayer against the attack of the hydroxyl radical.

Copper↗
PubMed1998

Polyelectrolyte-induced domains in lipid bilayer membranes: the deuterium NMR perspective.

Domain formation in lipid bilayer membranes can occur through electrostatic interactions between charged lipids and oppositely charged polyelectrolytes, such as proteins or polynucleic acids. This review describes a novel method for examining such domains in lipid bilayers, based on 2H NMR spectroscopy. The 2H NMR spectrum of choline-deuterated phosphatidylcholine is sensitive to, and reports on, lipid bilayer surface charge. When a charged lipid bilayer is exposed to an oppositely charged polyelectrolyte, the latter binds electrostatically to the bilayer surface and attracts charged lipids into its vicinity. The resulting inhomogeneous charge distribution produces overlapping 2H NMR subspectra arising from phosphatidylcholine within charge-enriched versus charge-depleted regions. Such spectral details as the quadrupolar splittings and the relative intensities of the subspectra permit a complete analysis of the domain composition, size, and, within limits, lifetime. Using 2H NMR, domain formation in lipid bilayer membranes can be observed with both cationic and anionic polyelectrolytes, whether of natural or synthetic origin. Domain size and composition prove to be sensitive to the detailed chemical structure of both the polyelectrolyte and the charged lipids. Within the domains there is always a stoichiometric anion/cation binding ratio, indicating that the polyelectrolyte lies flat on the membrane surface. The amount of phosphatidylcholine within the domain varies as a function of its statistical availability, in accordance with the predictions of a recent thermodynamic model of domain formation. When the molecular weight of the polyelectrolyte is varied, the domain size alters in accordance with the predictions of classical polymer physics. As expected for a predominantly electrostatic phenomenon, the observed domains dissipate at high ionic strength.

Chemical Phenomena↗
PubMed2000

Affinity of polyphenols for lipid bilayers.

Interaction of tea catechins with lipid bilayers has been investigated with liposome systems. Epicatechin gallate had the highest affinity for lipid bilayers, followed by epigallocatechin gallate, epicatechin, and epigallocatechin. Epicatechin gallate and epigallocatechin gallate in the surface of lipid bilayer perturbed the membrane structure.

Animals↗
PubMed2000

Conformational and orientation studies of artificial ion channels incorporated into lipid bilayers.

The conformational and orientation studies in lipid bilayers of 21 amino acid peptides bearing six crown ethers are reported. The compounds were designed to form artificial ion channels by stacking the crown rings, and were shown to be functional in bilayer membranes. We used Fourier transform infrared spectroscopy and CD spectropolarimetry to study the conformation of the peptides in solution and in lipid bilayers. These studies revealed that hexacrown peptides retain their alpha-helical conformation when incorporated in a lipid bilayer environment. Attenuated total reflectance spectroscopy was used to investigate the orientation of the peptides in a lipid bilayer. Results demonstrated that the peptides are not oriented at a fixed angle in membrane, but rather are in incorporation equilibrium between an active state parallel to the lipid chain and an inactive state adsorbed at the surface of the bilayer. From these results, we propose a model for the channel activity and the gating mechanism of these hexacrown peptides in bilayer membranes.

Animals↗
PubMed2004

Visualization of plasma membrane compartmentalization with patterned lipid bilayers.

Micrometer-size patterned lipid bilayers containing liganded lipids are used to control the location and size of receptor clusters and enable direct visualization of structural reorganization of cellular components. Subsequent to concentration of Fcepsilon receptor I, the mast cell receptor for IgE, and colocalized tyrosine phosphorylation activity, Lyn kinase and other proteins anchored to the inner leaflet of the plasma membrane redistribute selectively with the receptor clusters in a process that depends on actin polymerization. Surprisingly, outer leaflet components characteristically associated with lipid rafts do not detectably coredistribute with these inner leaflet components. Cell activation using patterned surfaces provides unique insights into cell membrane structural organization, revealing dynamic, large-scale uncoupling of inner and outer leaflet components of lipid rafts.

Actins↗
PubMed2002

Dynorphin induced magnetic ordering in lipid bilayers as studied by (31)P NMR spectroscopy.

Lipid bilayers of dimyristoyl phosphatidylcholine (DMPC) containing opioid peptide dynorphin A(1-17) are found to be spontaneously aligned to the applied magnetic field near at the phase transition temperature between the gel and liquid crystalline states (T(m)=24 degrees C), as examined by 31P NMR spectroscopy. The specific interaction between the peptide and lipid bilayer leading to this property was also examined by optical microscopy, light scattering, and potassium ion-selective electrode, together with a comparative study on dynorphin A(1-13). A substantial change in the light scattering intensity was noted for DMPC containing dynorphin A(1-17) near at T(m) but not for the system containing A(1-13). Besides, reversible change in morphology of bilayer, from small lipid particles to large vesicles, was observed by optical microscope at T(m). These results indicate that lysis and fusion of the lipid bilayers are induced by the presence of dynorphin A(1-17). It turned out that the bilayers are spontaneously aligned to the magnetic field above T(m) in parallel with the bilayer surface, because a single 31P NMR signal appeared at the perpendicular position of the 31P chemical shift tensor. In contrast, no such magnetic ordering was noted for DMPC bilayers containing dynorphin A(1-13). It was proved that DMPC bilayer in the presence of dynorphin A(1-17) forms vesicles above T(m), because leakage of potassium ion from the lipid bilayers was observed by potassium ion-selective electrode after adding Triton X-100. It is concluded that DMPC bilayer consists of elongated vesicles with the long axis parallel to the magnetic field, together with the data of microscopic observation of cylindrical shape of the vesicles. Further, the long axis is found to be at least five times longer than the short axis of the elongated vesicles in view of simulated 31P NMR lineshape.

Dimyristoylphosphatidylcholine↗
PubMed2006

Electrophysiological recordings of single ion channels in planar lipid bilayers using a polymethyl methacrylate microfluidic chip.

Planar lipid bilayers are used for functional studies of ion channel proteins using electrophysiological techniques. We have been developing a plastic micro-fluidic device for the reconstitution of planar lipid bilayers and electrophysiological recordings toward a "membrane protein chip" for high-throughput screening. In the previous report [Suzuki, H., Tabata, K.V., Noji, H., Takeuchi, S., 2006. Highly reproducible method of planar lipid bilayer reconstitution in polymethyl methacrylate microfluidic chip. Langmuir 22 (4), 1937-1942], we presented the method and device in which the reproducibility of planar lipid bilayers reached 90%, and multiple bilayers were formed simultaneously. In this communication, we show that our device has excellent electric properties suitable for ion channel analysis down to single molecular level. Additional aspects on the optical accessibility and controllability on lipid bilayer formation are also presented.

Electrochemistry↗
PubMed2005

Complementary matching in domain formation within lipid bilayers.

Domain structure and formation in lipid bilayers are investigated by molecular dynamics simulations using a coarse-grained lipid model. The lipid bilayers consist of two lipid types that are identical except for tail length. At a temperature intermediate to the two melting temperatures of the constituent lipid types, gel domains spontaneously form from an initial random structure. The simulations reveal that the gel domains consist of both lipid types in a complementary match. If a long lipid is in the top monolayer, then a short lipid is underneath and vice versa. The gel domains have a larger thickness than the surrounding liquid phase. The thickness of the gel domains is close to that of the pure long lipid gel phase bilayers. However, since in the mixed gel domains the lipids are not tilted and in the pure gel phase the lipids are tilted, the two thicknesses are similar, and the underlying structure is therefore not distinguishable solely by thickness measurements.

Gels↗
PubMed2006

Phase behavior and the partitioning of caveolin-1 scaffolding domain peptides in model lipid bilayers.

The membrane binding and model lipid raft interaction of synthetic peptides derived from the caveolin scaffolding domain (CSD) of the protein caveolin-1 have been investigated. CSD peptides bind preferentially to liquid-disordered domains in model lipid bilayers composed of cholesterol and an equimolar ratio of dioleoylphosphatidylcholine (DOPC) and brain sphingomyelin. Three caveolin-1 peptides were studied: the scaffolding domain (residues 83-101), a water-insoluble construct containing residues 89-101, and a water-soluble construct containing residues 89-101. Confocal and fluorescence microscopy investigation shows that the caveolin-1 peptides bind to the more fluid cholesterol-poor phase. The binding of the water-soluble peptide to lipid bilayers was measured using fluorescence correlation spectroscopy (FCS). We measured molar partition coefficients of 10(4) M(-1) between the soluble peptide and phase-separated lipid bilayers and 10(3) M(-1) between the soluble peptide and bilayers with a single liquid phase. Partial phase diagrams for our phase-separating lipid mixture with added caveolin-1 peptides were measured using fluorescence microscopy. The water-soluble peptide did not change the phase morphology or the miscibility transition in giant unilamellar vesicles (GUVs); however, the water-insoluble and full-length CSD peptides lowered the liquid-liquid melting temperature.

Adsorption↗
PubMed1987

Theory of passive proton conductance in lipid bilayers.

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.

Biological Transport↗