Conformation and mode of organization of amphiphilic membrane components: a conformational analysis (original) (raw)
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Monolayer Properties of 1,3-Diamidophospholipids
Langmuir, 2013
While nature provides an endless variety of phospholipids presenting hydrolyzable ester linkages for the 1,2-positioned hydrocarbon tails, we designed and synthesized 1,3-diamidophospholipids which contain stable fatty acid amides. These new phospholipids form faceted unilamellar vesicles with mechanosensitive properties. Aiming to understand the mechanism responsible for this behavior at a molecular level, we investigated the 1,3-diamidophospholipid family in monolayers, a simplified model membrane system. Langmuir isotherms combined with in situ grazing incidence X-ray diffraction (GIXD), specular X-ray reflectivity (XR), and infrared reflection−absorption spectroscopy (IRRAS) allowed the characterization of the monolayers from a structural and thermodynamical point of view. The existence of strong headgroup interactions due to the formation of a hydrogen-bonding network was clearly revealed by IRRAS and by the high rigidity of the monolayers. GIXD showed that only the longer chain compounds of the series (Pad-PC-Pad (1,3dipalmitamidopropan-2-phosphocholine) and Sad-PC-Sad (1,3-distearamidopropan-2-phosphocholine) were able to form ordered monolayers. The chains are strongly tilted in a rigid lattice formed due to these hydrogenbonding interactions between the headgroups. The thermodynamical analysis leads to a critical temperature of the monolayer which is clearly different from the main phase transition temperature in bulk, indicating that there must be a different structural arrangement of the 1,3-diamidophospholipids in monolayers and in bilayers.
Influence of ether linkages on the structure of double-chain phospholipid monolayers
Chemistry and Physics of Lipids, 1995
The structure c,f phosphatidylcholine monolayers has been studied by Synchrotron X-ray diffraction at the air/water interface varying the ester and ether linkages of the aliphatic tails at the glycerol backbone. All systems investigated exhibit an oblique lattice structure with extremely large tilt angles of the chains from vertical, even at high lateral pressures. Although no large difference is seen in the isotherms, the replacement of ester by ether linkages causes a reduction of the tilt angle and of the area per molecule. These changes also depend on the position of the ether group with respect to the glycerol backbone and can be understood within a model where the carbonyl group of the ester at the C2 position pulls the attached chain towards the water subphase.
Phospholipid interactions in model membrane systems. I. Experiments on monolayers
Biophysical Journal, 1992
We study the lateral headgroup interactions among phosphatidylcholine (PC) molecules and among phosphatidylethanolamine (PE) molecules in monolayers and extend our previous models. In this paper, we present an extensive set of pressure-area isotherms and surface potential experiments on monolayers of phospholipids ranging from 14 to 22 carbons in length at the n-heptane/water interface, over a wide range of temperature, salt concentration, and pH on the acid side. The pressure data presented here are a considerable extension of previous data (1) to higher surface densities, comprehensively checked for monolayer loss, and include new data on PE molecules. We explore surface densities ranging from extremely low to intermediate, near to the main phase transition, in which range the surface pressures and potentials are found to be independent of the chain length. Thus, these data bear directly on the headgroup interactions. These interactions are observed to be independent of ionic strength. PC and PE molecules differ strongly in two respects: (a) the lateral repulsion among PC molecules is much stronger than for PE, and (b) the lateral repulsion among PC molecules increases strongly with temperature whereas PE interactions are almost independent of temperature. Similarly, the surface potential for PC is found to increase with temperature whereas for PE it does not. In this and the following paper we show that these data from dilute to semidilute monolayers are consistent with a theoretical model that predicts that, independent of coverage, for PC the P-N+ dipole is oriented slightly into the oil phase because of the hydrophobicity of the methyl groups, increasingly so with temperature, whereas for PE the P-N+ dipole is directed into the water phase.
The hydrophobic acyl-chain effect in the lipid domains appearance through phospholipid bilayers
Journal of Molecular Structure: THEOCHEM, 1998
An intermolecular interaction model for selective association processes of double-chain phospholipids in bilayer lipid membranes has been proposed, analysed and solved numerically. A large variety of binary mixtures of asymmetrical double-chain phospholipids with the cross-sectional areas of the polar headgroups a 1 40 Å 2 (the first component) and a 2 60 Å 2 (the second component) have been investigated. Changing the hydrophobic acyl-chain lengths of both mixture components, we found in all cases that the self-association probability (the association of like-pairs of phospholipids) of the first component in parallel alignment of the electric dipole moments of the polar headgroups is higher than the cross-association probability (the association of cross-pairs of phospholipids) and the self-association probability of the second component. This result is in good agreement with the experimental evidence that where the cross-sectional area of the polar headgroups matches the hydrocarbon chain-packing cross-sectional area (a ഡ 2S ഡ 40 Å 2 ), lipids possess a high tendency to aggregate into well packed bilayer structures with the acyl-chains oriented perpendicularly to the bilayer plane. Our theoretical data confirm that the double-chain phospholipids may associate themselves into anti-parallel alignment of the polar headgroups (P H 22 ) as well. The hydrophobic acyl-chain effect of phospholipids may modulate the distribution of lipid domains within bilayers that have a large variety of functional roles in cellular metabolism. ᭧
Effects of phospholipid unsaturation on the bilayer nonpolar region: a molecular simulation study
The Journal of Lipid Research, 2003
Molecular dynamics simulations of two monounsaturated phosphatidylcholine (PC) bilayers made of 1-palmitoyl-2-oleoyl-PC (POPC; cis -unsaturated) and 1-palmitoyl-2-elaidoyl-PC (PEPC; trans -unsaturated) were carried out to investigate the effect of a double bond in the PC  -chain and its conformation on the bilayer core. Four nanosecond trajectories were used for analyses. A fully saturated 1,2-dimyristoyl-PC (DMPC) bilayer was used as a reference system. In agreement with experimental data, this study shows that properties of the PEPC bilayer are more similar to those of the DMPC than to the POPC bilayer. The differences between POPC and PEPC bilayers may be attributed to the different ranges of angles covered by the torsion angles  10 and  12 of the single bonds next to the double bond in the oleoyl (O) and elaidoyl (E) chains. Broader distributions of  10 and  12 in the E chain than in the O chain make the E chain more flexible. In effect, the packing of chains in the PEPC bilayer is similar to that in the DMPC bilayer, whereas that in the POPC bilayer is looser than that in the DMPC bilayer. The effect of the cis -double bond on torsions at the beginning of the O chain (  4 and  5) is similar to that of cholesterol on these torsions in a myristoyl chain. -Róg, T., K. Murzyn, R. Gurbiel, Y. Takaoka, A. Kusumi, and M. Pasenkiewicz-Gierula. Effects of phospholipid unsaturation on the bilayer nonpolar region: a molecular simulation study. J. Lipid Res. 2004. 45: 326-336. Supplementary key words phosphatidylcholine • cis double bond • trans double bond • skew conformation • chain packing
Langmuir, 2019
Knowledge of the thermotropic phase behavior of solid-supported bilayer lipid assemblies is essential for mimicking the molecular organization and lateral fluidity of cell membranes. The gelto-fluid phase transitions in a homologous series of single phospholipid bilayers supported on planar silicon substrates were investigated by temperature-controlled atomic force microscopy (AFM) and attenuated total reflection infrared (ATR-IR) spectroscopy to obtain complementary information at the mesoscopic and molecular scales. Symmetric bilayers of dipalmitoylphosphatidylcholine (DPPC) and vertically asymmetric bilayers comprised of a leaflet of DPPC and another of acyl-chain-deuterated DPPC (DPPC-d62) were prepared by the Langmuir-Blodgett technique. The selective deuteration of one of the bilayer leaflets enabled the simultaneous monitoring by IR spectroscopy of the acyl chain melting in each leaflet via the spectrally isolated CH2 and CD2 stretching vibrations. Two gel-to-fluid transitions were discerned for both the symmetric and asymmetric bilayers in ultrapure water. The deuterium isotope effect observed in free-standing membranes was maintained for the supported bilayers. IR spectroscopy revealed that the melting of one leaflet promotes the disordering of the acyl chains in the adjacent one. The findings suggest that the two leaflet phase transitions do not evolve in isolation. This work sheds insight into the nature of leaflet-leaflet interactions and the thermodynamic properties of surface-confined phospholipid bilayers.