Model Phospholipid Bilayers Research Articles

Interaction of an odorant lactone with model phospholipid bilayers and its strong fluidizing action in yeast membrane

Some odorant lactones are naturally present in fruits or in fermented products; they can also be used as food additives and can be produced by microorganisms at the industrial scale by biotechnological processes. γ-Decalactone was previously shown to have antimicrobial properties. We determined by infrared spectroscopy measurements that this compound rapidly diffused into model phospholipid bilayers (within 2 min), modifying the general physical state of a dimyristoyl- l-α-phosphatidylcholine (DMPC) film. In vivo, the lactone strongly increased membrane fluidity in the model yeast Yarrowia lipolytica, as evaluated by fluorescence anisotropy measurements. This effect was more important than that of benzyl alcohol, which is known as a fluidizing agent in living cells, and may explain the toxic action of γ-decalactone in microorganisms.

Electrostatic interactions in a neutral model phospholipid bilayer by molecular dynamics simulations

The organization of the lipid headgroups in a neutral model membrane is studied by atomistic simulations in the fluid lamellar phase, Lα. In particular, we report the results obtained for a fully hydrated 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine lipid bilayer at room temperature. The orientational distribution of the lipid dipole moments with respect to the membrane normal presents a maximum at 70° (20° above the plane of the interface, pointing toward the water region). We also found another smaller peak at 110° (−20° with respect to the membrane plane). This preferential orientation of the lipid headgroup dipoles with respect to the bilayer normal obtained at 303 K is qualitatively different from previous calculations at higher temperatures in the fluid lamellar phase, where headgroup dipoles were uniformly distributed with orientations spanning 0°–135°. Despite their differences, both situations give rise to a similar mean orientation of ∼70°, which is in excellent agreement with experiment. The statistics of the main lipid–lipid interactions, the charge density profiles, the electrostatic potential along the bilayer normal, and the polarization of water molecules at the interfacial plane are also analyzed.

Localization of bilirubin in phospholipid bilayers by parallax analysis of fluorescence quenching

It has been proposed that the neurotoxicity observed in severely jaundiced infants results from the binding of unconjugated bilirubin to nerve cell membranes. However, despite potentially important clinical ramifications, there remains significant controversy regarding the physical nature of bilirubin-membrane interactions. We used the technique of parallax analysis of fluorescence quenching (Chattopadhyay, A., and E. London. 1987. Biochemistry. 26: 39–45) to measure the depth of penetration of bilirubin in model phospholipid bilayers. The localization of unconjugated bilirubin and ditaurobilirubin within small unilamellar vesicles composed of dioleoylphosphatidylcholine was determined through an analysis of the quenching of bilirubin fluorescence by spin-labeled phospholipids, and by bilirubin-mediated quenching of a series of anthroyloxy fatty acid probes at various depths within the membrane bilayer. Findings were further verified with potassium iodide as an aqueous quencher. Our results indicate that, at pH 10, unconjugated bilirubin localizes approximately 20 Å from the bilayer center, in the region of the polar head groups. Further analyses suggest a modest influence of pH, membrane cholesterol content, and vesicle diameter on the bilirubin penetration depth. Taken together, these data support that, under physiologic conditions, bilirubin localizes to the polar region of phospholipid bilayers, near the membrane-water interface. —Zucker, S. D., W. Goessling, E. J. Bootle, and C. Sterritt. Localization of bilirubin in phospholipid bilayers by parallax analysis of fluorescence quenching.

HgCl 2 disrupts the structure of the human erythrocyte membrane and model phospholipid bilayers

The structural effects of Hg(II) ions on the erythrocyte membrane were studied through the interactions of HgCl 2 with human erythrocytes and their isolated resealed membranes. Studies were carried out by scanning electron microscopy and fluorescence spectroscopy, respectively. Hg(II) induced shape changes in erythrocytes, which took the form of echinocytes and stomatocytes. This finding means that Hg(II) locates in both the outer and inner monolayers of the erythrocyte membrane. Fluorescence spectroscopy results indicate strong interactions of Hg(II) ions with phospholipid amino groups, which also affected the packing of the lipid acyl chains at the deep hydrophobic core of the membrane. HgCl 2 also interacted with bilayers of dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, representative of phospholipid classes located in the outer and inner monolayers of the erythrocyte membrane, respectively. X-ray diffraction indicated that Hg(II) ions induced molecular disorder to both phospholipid bilayers, while fluorescence spectroscopy of dimyristoylphosphatidylcholine large unilamellar vesicles confirmed the interaction of Hg(II) ions with the lipid polar head groups. All these findings point to the important role of the phospholipid bilayers in the interaction of Hg(II) on cell membranes.

The Anticancer Drug Chlorambucil Interacts with the Human Erythrocyte Membrane and Model Phospholipid Bilayers

The plasma membrane has gained increasing attention as a possible target of antitumor drugs. It has been reported that they act as growth factor antagonists, growth factor receptor blockers, interfere with mitogenic signal transduction or exert direct cytotoxic effects. Chlorambucil (4-[p-(bis[2-chloroethyl]amino)phenyl]butyric acid) is an alkylating agent widely used in the treatment of chronic lymphocytic leukaemia. Contradictory reports have been published concerning its interaction with cell membranes. Whereas a decrease in the fluidity of Ehrlich ascite tumor cells has been adduced, no evidences were found that chlorambucil changes membrane lipid fluidity and alkylating agents had effects in these systems even at highly toxic concentrations. Our results showed that chlorambucil at a dose equivalent to its therapeutical concentration in the plasma (3.6 microM) caused the human erythrocyte membrane to develop cup-shaped forms (stomatocytes). Accordingly to the bilayer couple hypothesis, this means that the drug is inserted into the inner monolayer of the erythrocyte membrane, a conclusion supported by X-ray diffraction performed on multilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the erythrocyte membrane, respectively. It is concluded that the cytotoxic effect of chlorambucil might be due to alteration of the structure and therefore of the physiological properties of cell membranes such as fluidity, permeability, receptor and channel functions.

Interactions of Al(acac) 3 with cell membranes and model phospholipid bilayers

Aluminum is a neurotoxic agent; however, little information has been obtained regarding its molecular cytotoxicity and the effects on the stability of biological membranes. This is mainly due to the ill-defined chemical speciation of the metal compounds. For this reason, the present study used aluminum acetylacetonate, (Al(acac) 3), a neutral, chemically well-defined, hydrolytically stable andlipophilic compound. To understand the molecular mechanism of its interaction with cell membranes, Al(acac) 3 was incubated with human erythrocytes, isolated toad skin and molecular models of biomembranes. The latter consisted of multilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoyphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. The results showed that Al(acac) 3 interacted with the erythrocyte membrane modifying its normal discoid morphology to both echinocytic and stomatocytic shapes. This finding indicates that the Al complex was inserted in both the outer and inner layers of the red cell membrane, a conclusion supported by X-ray diffraction analyses of DMPC and DMPE bilayers. Electrophysiological measurements performed on toad skin revealed a significant decrease in the potential difference and short-circuit current responses after application of Al(acac) 3, effects interpreted to reflect inhibition of the active transport of ions. Al(acac) 3 was active on both surfaces of the skin suggesting that the membrane was permeated by the metal complex. It is concluded that Al(acac) 3 both alters the molecular structure of the lipid bilayer, thereby modifying the biophysical properties of the cell membrane, and changes its physiological properties.

Interaction of Indolicidin with Model Lipid Bilayers: FTIR-ATR Spectroscopic Study

An attempt has been made using Fourier transform infrared−attenuated total reflection (FTIR-ATR) spectroscopy to see the molecular level interaction between indolicidin, a tridecapeptide known to possess antimicrobial activity, and model phospholipid bilayers. Initially, model lipid bilayers were assembled on ZnSe plates with compounds of dipalmitoylphosphatidic acid (DPPA), dipalmitoylphosphatidylcholine (DPPC), and dipalmitoylphosphatidylglycerol (DPPG) using the Langmuir−Blodgett (LB) method. From the FTIR-ATR dichroic ratios measured with and without rotation of the ATR plates, the LB lipid bilayers seemed to be described in terms of a uniaxial orientational model. Along with a cyclovoltammetry measurement, the ATR spectra dictated that indolicidin molecules were readily incorporated inside the acyl chains of the lipid bilayers. Furthermore, from the infrared absorption frequencies of amide I bands, indolicidin molecules that consisted of ill-defined random-coil structures in an aqueous medium appeare...

Interfacial Catalysis by Human 85 kDa Cytosolic Phospholipase A2 on Anionic Vesicles in the Scooting Mode

Analysis of phospholipases A2 on model phospholipid bilayers in which enzyme is essentially irreversibly bound at the lipid-water interface, termed "scooting mode", is a useful tool for studying the kinetic properties of interfacial enzymes. It is shown that human cytosolic 85 kDa phospholipase A2 (cPLA2) hydrolyzes sn-2-arachidonyl-containing phospholipids or the gamma-linolenoyl ester of 7-hydroxycoumarin (GLU) dispersed in vesicles of 1,2-dioleoyl-sn-glycero-3-phosphomethanol (L-DOPM) in the scooting mode. Trapping of cPLA2 on L-DOPM vesicles is rapid and independent of product formation. Slowing of cPLA2-catalyzed hydrolysis of substrates present in phosphatidylmethanol and phosphatidylcholine vesicles is primarily due to apparent inactivation rather than to substrate depletion. cPLA2 phosphorylated on serine 505 by mitogen-activated protein kinase displays a 30% increase in the rate of sn-2-arachidonylphosphatidylcholine hydrolysis in the scooting mode compared to that of the nonphosphorylated enzyme. Kinetic parameters of cPLA2 acting on a variety of different phosphatidylmethanol vesicles were evaluated, and the results are discussed in terms of active site affinities for substrates and of lateral organization of substrates in the bilayer. A key result is that the sigmoidal kinetics reported previously using 1,2-dimyristoyl-sn-glycero-3-phosphomethanol (DMPM) vesicles are most prominent near the phase transition temperature of DMPM. No sigmoidal kinetics was observed using L-DOPM vesicles. The results of kinetic experiments and the behavior of a fluorescent substrate analog are consistent with nonideal mixing of substrate in DMPM vesicles, but not in L-DOPM vesicles, suggesting that apparent saturation and sigmoidal kinetics are more a result of nonideal mixing of substrate in DMPM vesicles than of active site binding of substrate. The fluorescence assay described using L-DOPM/GLU vesicles is useful for evaluating the interfacial behavior of cPLA2, including its substrate preferences and the effect of active site-directed inhibitors.

On the Mechanism of Hormone Recognition and Binding by the CCK-B/Gastrin Receptor

Lipidation with long-chain di-fattyacyl-glycerol moieties was used to anchor gastrin in CCK peptides irreversibly to lipid bilayers lipopeptide transfer to model phospholipid bilayers is fast and quantitative, leading to a different mode of insertion of lipo-gastrin and lipo-CCK in lipid layers. Lipo-gastrin remains exposed to the bulk solvent in a predominantly random coil structure as a consequence of electrostatic repulsion, whereas lipo-CCK exhibits a pronounced tendency to form peptide domains with insertion of its C-terminus into more hydrophobic compartments of the bilayers. Thereby Ca2+ at physiological concentrations favours this aggregational phenomenon. Since both lipo-peptides were found to retain almost full receptor affinity despite their irreversible anchorage to the bilayer, a membrane-bound pathway in the receptor recognition and binding process is indeed possible. According to the data collected in this study, CCK might possibly use this pathway, whereas accumulation of gastrin on the cell membrane with prefolding of the ligand at the water/lipid interface is hardly conceivable. Nevertheless the observed receptor interaction of the deliberately membrane-anchored gastrin offers interesting constraints for computational docking experiments on a modelled CCK-B/gastrin receptor by additionally taking into account information derived from mutagenesis studies. Despite the limitations of such modelling experiments, the resulting picture of the gastrin/receptor complex allowed the visualization and rationalization of the experimental results of the extensive structure-function studies performed previously on this family of gastrointestinal hormones.

Transverse Membrane Asymmetry in Model Phospholipid Bilayers: NBD-Phosphatidylethanolamine and the Separation of Flip from Flop

Transverse Membrane Asymmetry in Model Phospholipid Bilayers: NBD-Phosphatidylethanolamine and the Separation of Flip from Flop

Specific binding of avidin to biotin containing lipid lamella surfaces studied with monolayers and liposomes.

The interaction of avidin (from egg white) with phospholipid (monolayer and bilayer) model membranes containing biotin-conjugated phospholipids has been studied. In the first part, using surface sensitive techniques (ellipsometry and surface plasmon resonance) we demonstrated that the nonspecific adsorption of avidin to phospholipid lamella could be abolished by adding an amount of Ca2+, Mg2+ or Ba2+ that led to an electrostatic interaction. The specific binding of avidin to lipid mixtures containing biotin-conjugated phospholipids was obviously composition dependent. The ratio 1:12 of a B-DPPE/DPPE mixture was found to be the optimum molar ratio. When we compared the results from the surface sensitive techniques with those from the electron micrographs of a two dimensional crystal of avidin (obtained in our laboratory), the optimum ratio was found to be determined by the effect of lateral steric hindrance. In the second part, we observed the pattern of the layers of fluorescently labeled phospholipid and adsorbed proteins with a home-made micro fluorescence film balance. The fluorescence images showed that avidin was preferentially bound to the receptors that were in the fluid domains. Further, with a sensitive fluorescence assay method, the effect of the phase behavior of liposomes on the specific binding of avidin was measured. This showed that avidin interacted with biotinlipid more weakly in the gel state liposome than in the liquid state liposome. The major conclusion was that the binding of avidin to a membrane bound model receptor was significantly restricted by two factors: one was the lateral steric hindrance and the other was the fluidity of the model membrane.

Calculations of the electrostatic potential adjacent to model phospholipid bilayers

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 < 11% acidic lipid, the -25 mV 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.

Structural characterization and nanometer-scale domain formation in a model phospholipid bilayer as determined by infrared spectroscopy and scanning tunneling microscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructural characterization and nanometer-scale domain formation in a model phospholipid bilayer as determined by infrared spectroscopy and scanning tunneling microscopyBrian W. Gregory, Richard A. Dluhy, and Lawrence A. BottomleyCite this: J. Phys. Chem. 1994, 98, 3, 1010–1021Publication Date (Print):January 1, 1994Publication History Published online1 May 2002Published inissue 1 January 1994https://doi.org/10.1021/j100054a044RIGHTS & PERMISSIONSArticle Views206Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts

Surface-differentiated model phospholipid bilayers

Dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) were synthesized in which the head groups were covalently functionalized with p-nitrophenyl benzoate (PNPB) moieties. Liposomes composed of 1 part functional lipid and 7 parts nonfunctional DPPC or DOPC were created at pH 6 and subjected to an exovesicular/endovesicular 12/6 pH gradient

A COMPUTER STUDY OF A SIMPLE STATISTICAL-MECHANICAL MODEL OF PHOSPHOLIPID MONOLAYERS AND BILAYERS

Both the phase diagram and the phase-transition dynamics are studied for a simple model of phospholipid monolayers and bilayers. The phase diagram is studied using finite size scaling and phenomenological renormalization. The model predicts a first-order phase transition with a critical point. The phase-transition dynamics is investigated by the Monte Carlo method with Glauber dynamics. After quenching the system below the critical temperature, the average size of the growing domains l(t) is found to follow a t1/2 law.

Studies of membrane dynamics using nitroxide spin labels

Abstract

Complete proton magnetic resonance in whole cells

The proton magnetic resonance spectrum of whole cells is a complex, composite spectrum with a myriad of dipolar broadened (“broadline”) and non-dipolar-broadened (“high-resolution”) contributions. Methods of separating and characterizing the different types of components are described and developed using a phospholipid bilayer model membrane and the R13762 rat mammary adenocarcinoma cell line. It was found that 35 ± 2% of the protons in the 1H NMR spectrum of the R13762 cells are associated with the high-resolution spectrum. Of the remaining 65%, approximately 40% can be assigned to the characteristic fluid membrane dipolar-broadened, super-Lorentzian lines. A further 20% can be assigned to dipolar-broadened lines from membrane proteins and the last 5% to non-dipolar-broadened lines of width several hundred hertz, from rigid parts of cytoplasmic proteins. Quantitative analysis of the narrow methylene peak, which has been used to characterize the metastatic properties of R13762 cells, shows that it contains 7.3 ± 1.6% of all the protons in the cell. The introduction of spectroscopic selection methods such as the CPMG pulse sequence and the Jeener-Broekaert echo sequence has made it possible to simultaneously analyze the broadline and high-resolution characteristics of an intact viable cell.

On the ordering of N-alkane and N-alcohol solutes in phospholipid bilayer model membrane systems

2H-NMR measurements of the ordering of several n-alkane and one n-alcohol solutes in lipid bilayers formed from dimyristoyl lecithin (DML) are reported. The results are consistent with orientation of the solutes between the lipid chains, the n-alkanes having a preference for the bilayer interior, while the n-octanol is anchored at the bilayer surface. Solubility of the short chain n-alkanes, n-hexane and n-octane as an ordered component in the L α phase is more limited than that of n-dodecane. The NMR data are supported by low angle X-ray diffraction results which confirm that n-octanol has a more dramatic influence on bilayer area than the n-alkanes.

Deuterium magnetic resonance of human plasma lipoproteins

Palmitic-d 31 acid was incorporated into human plasma low and high density lipoproteins by incubation of lipoprotein dispersions with the fatty acid. 2H NMR spectra were obtained and indicate that acyl chain order is higher in the surface monolayer of lipoproteins than in model phospholipid bilayer membranes. Thus the method can usefully be applied to investigate molecular motion within the monolayer of native lipoproteins.

Molecular structure and interaction of dipalmitoyl phosphatidylcholine in multilayers. Comparative study with phosphatidylethanolamine

As a model of phospholipid bilayers in solid an oriented multilayer film (built-up film) of L-α-dipalmitoyl phosphatidylcholine (DPPC) was prepared from the monolayer by the dipping method. Structural analysis has been carried out by measuring infrared dichroism of the built-up film. The results were compared with those of the built-up film of L-α-dipalmitoyl phosphatidylethanolamine (DPPE). The tilting of the hydrocarbon chains is larger for DPPC than for DPPE. The orientation of the bisector of the two non-esterified PO bonds is closer to the film plane for DPPC than for DPPE. The strong hydrogen bonding interaction between the polar head groups was shown for DPPE, but not for DPPC. These features resemble the structural differences between dilauroyl phosphatidylethanolamine (DLPE) and dimyristoryl phosphatidylcholine (DMPC) in crystals. The hydrogen bonding interaction of DPPE found in solid remains even in the presence of water, namely, in the gel state. More closed packing of the hydrocarbon chains of solid DPPE than DPPC in solid was concluded on the basis of infrared and Raman spectra.