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1.
The effect of rigid inclusions on the phase behavior of a film containing a mixture of lipid molecules is investigated. In
the proposed model, the inclusion-induced deformation of the film, and the resulting energy cost are strongly dependent upon
the spontaneous curvature of the mixed film. The spontaneous curvature is in turn strongly influenced by the composition of
film. This coupling between the film composition and the energy per inclusion leads to a lateral modulation of the composition,
which follows the local curvature of the membrane. In particular, it is shown that inclusions may induce a global phase separation
in a film which would otherwise be homogeneously mixed. The mixed film is then composed of patches of different average composition,
separated by the inclusions. This process may be of relevance to explain some aspects of lipid-protein association in biological
membranes.
Received 8 April 1999 and Received in final form 4 October 1999 相似文献
2.
G. La Penna S. Letardi V. Minicozzi S. Morante G.C. Rossi G. Salina 《The European physical journal. E, Soft matter》2001,5(3):259-274
In this paper we present the results of a large-scale numerical investigation of structural properties of a model of cell
membrane, simulated as a bilayer of flexible molecules in vacuum. The study was performed by carrying out extensive Molecular
Dynamics simulations, in the (NVE) micro-canonical ensemble, of two systems of different sizes ( 2×32 and 2×256 molecules), over a fairly large set of temperatures and densities, using
parallel platforms and more standard serial computers. Depending on the dimension of the system, the dynamics was followed
for physical times that go from few hundred picoseconds for the largest system to 5-10 nanoseconds for the smallest one. We
find that the bilayer remains stable even in the absence of water and neglecting Coulomb interactions in the whole range of
temperatures and densities we have investigated. The extension of the region of physical parameters that we have explored
has allowed us to study significant points in the phase diagram of the bilayer and to expose marked structural changes as
density and temperature are varied, which are interpreted as the system passing from a crystal to a gel phase.
Received 6 July 2000 and Received in final form 28 December 2000 相似文献
3.
King V Parker M Howard KP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,142(1):177-182
We report NMR data for magnetically oriented phospholipid bilayers which have been doped with a lipid derivatized with a polyethylene glycol polymer headgroup to stabilize samples against aggregation. (13)C, (31)P, and (2)H NMR data indicate that the incorporation of PEG2000-PE (1% molar to DMPC) does not interfere with the orientation properties of bicelles prepared at 25% w/v with or without the presence of lanthanide. Bicelles prepared at 10% w/v are also shown to orient when PEG2000-PE is added. The addition of PEG2000-PE to cholesterol-containing, lanthanide-flipped bicelles is shown to inhibit sample phase separation and improve spectral quality. Furthermore, the addition of PEG2000-PE to high w/v bicelles (40% w/v) is demonstrated to lead to an increase in overall sample order. 相似文献
4.
The grand canonical Monte Carlo technique is used to reveal the origin of the repulsive pressure operating between supported DLPC bilayers at short separations. By partitioning the interbilayer pressure into physically distinct components, it is shown that the short-range repulsion comes mainly from the direct electrostatic lipid–lipid interaction of the head groups in the opposing leaflets. By contrast, the electrostatic lipid–lipid interaction between DLPE bilayers is strongly attractive, and the short-range repulsion is associated with the hydration (water–lipid) interactions [A. Pertsin, D. Platonov, M. Grunze, Langmuir 23 (2007) 1388]. These findings explain why DLPC bilayers have a much larger interbilayer (fluid) separation at a given pressure, as compared to that for DLPE. 相似文献
5.
F. Sebastiani R. Harvey S. Khanniche J.-B. Artero M. Haertlein G. Fragneto 《The European physical journal. Special topics》2012,213(1):355-365
In this study we have used neutron diffraction to examine the swelling behaviour and bilayer parameters of membranes reconstituted from polar lipids extracted from B. subtilis and model systems composed of synthetic phospholipids. Evidence for phase separation in the model system (lacking in Lysyl-PG, L-PG) is discussed in relation to its possible contribution to membrane domain formation through lipid-lipid interactions. Comparing these results with those obtained from the bilayers composed of lipids extracted from bacterial cells gives us some indication of the role of L-PG in the B. subtilis plasma membrane. 相似文献
6.
Lateral organization of proteins in biomembranes is vitally important to membrane functions such as signal transduction, endocytosis,
and membrane trafficking. One of the major goals in current biomembrane science is to reveal the microscopic mechanism of
membrane-associated protein organization in biomembranes. Here, we investigate the structural organization of membrane-associated
proteins in lipid bilayers by combining self-consistent field theory with density functional theory. The present study can
simultaneously take into account the entropy effect of lipids, depletion effect of membrane-associated proteins due to the
presence of lipid headgroups as well as the effect of interfacial interaction. By varying the volume fraction of lipids, we
examine various effects on protein organization, and reveal that a close-packed crystal structure appears at low lipid volume
fractions due to interfacial energy and weak depletion effect, whereas a chain structure with branches occurs at high lipid
volume fractions mainly due to strong depletion. The present results may provide some theoretical insight into further experiments
on organization of membrane proteins. 相似文献
7.
We present a lattice model of the thermotropic transition in lipid bilayers which contain cholesterol. Changes in some observed quantities are accounted for and comments are made about the existence of a lipid boundary layer around a cholesterol. 相似文献
8.
A method enabling one to separate the contributions of repulsion and attraction forces resulting in frequency non-coincidences in liquids is presented. 相似文献
9.
Henryk Malak Ignacy Gryczynski Jonathan D. Dattelbaum Joseph R. Lakowicz 《Journal of fluorescence》1997,7(2):99-106
We observed the emission of l,6-diphenyl-l,3,5-hexatriene (DPH) when excited with the fundamental output of a fs Ti:sapphire
laser at 860 nm. The emission spectra of DPH were identical to that observed for one-photon excitation at 287 nm. The dependence
of the DPH emission intensity on laser power was cubic, indicating three-photon excitation of DPH at 860 nm. At a shorter
wavelength of 810 nm, the dependence on laser power was quadratic, indicating a two-photon process. At an intermediate wavelength
of 830 nm the mode of excitation was a mixture of two- and three-photon excitation. At 830 nm the anisotropy is no longer
a molecular parameter, and the mode of excitation and anisotropy of DPH depends on laser power. Frequency-domain anisotropy
decays of DPH in triacetin revealed the same rotational correlation times for two- and three-photon excitation. However, the
time 0 anisotropy of DPH was larger for three-photon excitation than for two-photon excitation. Steady-state anisotropy data
for DPH-labeled membranes revealed the same transition temperature for one- and three-photon excitation. These anisotropy
data indicate that membrane heating was not significant with three-photon excitation and that three-photon excitation may
thus be of practical usefulness in fluorescence spectroscopy and microscopy of membranes. 相似文献
10.
We have studied the temperature dependence of the stacking periodicity, d, of oriented phospholipid multilayers using grazing angle neutron scattering techniques. d is found to increase substantially at higher temperatures, just before the bilayers peel off from the substrate. Although we do not observe thermal unbinding, our results are consistent with the notion that the unbinding transition is driven by steric repulsion arising from thermal fluctuations of the membranes, in contrast to those of a recent study by Vogel et al. [Phys. Rev. Lett. 84, 390 (2000)]. 相似文献
11.
《Physica B+C》1981,103(1):8-20
The application of computer calculation techniques to the determination of phase equilibria in multicomponent systems is described. Examples of the use of such calculations in alloy development work and in metallurgical production processes are given. The importance of thermodynamic data banks for facilitating complex equilibrium calculations is demonstrated and the likely implications for future industrial operations are briefly discussed. It is concluded that the combination of computer calculation techniques with a much more restricted number of experimental measurements will in future lead to rapid and reliable determination of phase equilibria in multicomponent systems. 相似文献
12.
G. Erriu S. Onnis N. Zucca M. Casu A. Lai C. Giori G. Schianchi 《Il Nuovo Cimento D》1993,15(11):1451-1463
Summary The lipid composition of multi-lamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine exposed to137Cs γ-rays depends on the absorbed dose. In fact,31P and1H NMR analysis shows that four new molecular species are formed during the irradiation:a) 1-palmitoyl-sn-glycero-3-phosphorylcholine,b) 2-palmitoyl-sn-glycero-3-phosphorylcholine,c) glycerophosphorylcholine andd) free palmitic acid. Neglecting the speciesc), that is present only at high dose and in very small amount, the behaviour of molar fractionvs. dose is sublinear fora) andb), while ford) it is almost linear over all the dose range examined. The molecular and structural damage consequences onto the multi-lamellar
vesicles, evidentiated by spin-labelling and DSC techniques, are discussed. It is clearly shown in particular, that the behaviour
of the main transition does not depend on the concentration of the lysolecithins, but rather on that of the free palmitic
acid, the role of which had previously been entirely neglected.
The authors of this paper have agreed to not receive the proofs for correction. 相似文献
13.
T. Charitat E. Bellet-Amalric G. Fragneto F. Graner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):583-593
Single and double phosphocholine (DPPC and DSPC) bilayers adsorbed at the silicon-water interface have been prepared and characterised.
The second bilayer, called “free bilayer”, is a novel highly hydrated system floating at above the first one. Robust and reproducible preparation has been possible thanks to a combination of Langmuir-Blodgett and
Langmuir-Schaeffer techniques. Carefully optimised neutron reflectivity measurements have allowed a precise non-destructive
characterisation of the structure, hydration and roughness of the layers. This work opens new possibilities for the investigation
of the interaction between membrane lipids and soluble proteins, in particular peptides too small to be visible with other
techniques.
Received 17 July 1998 相似文献
14.
15.
Macdonald PM Crowell KJ Franzin CM Mitrakos P Semchyschyn D 《Solid state nuclear magnetic resonance》2000,16(1-2):21-36
2H NMR studies of polyelectrolyte-induced domain formation in lipid bilayer membranes are reviewed. The 2H NMR spectrum of choline-deuterated phosphatidylcholine (PC) reports on any and all sources of lipid bilayer surface charge, since these produce a conformation change in the choline head group of PC, manifest as a change in the 2H NMR quadrupolar splitting. In addition, homogeneous and inhomogeneous surface charge distributions are differentiated. Adding polyelectrolytes to lipid bilayers consisting of mixtures of oppositely charged and zwitterionic lipids produces 2H NMR spectra which are superpositions of two Pake sub-spectra: one corresponding to a polyelectrolyte-bound lipid population and the other to a polyelectrolyte-free lipid population. Quantitative analysis of the quadrupolar splittings and spectral intensities of the two sub-spectra indicate that the polyelectrolyte-bound populations is enriched with oppositely charged lipid, while the polyelectrolyte-free lipid population is correspondingly depleted. The same domain-segregation effect is produced whether cationic polyelectrolytes are added to anionic lipid bilayers or anionic polyelectrolytes are added to cationic lipid bilayers. The 2H NMR spectra permit a complete characterization of domain composition and size. The anion:cation ratio within the domains is always stoichiometric, as expected for a process driven by Coulombic interactions. The zwitterionic lipid content of the domains is always statistical, reflecting the systems tendency to minimize the entropic cost of demixing charged lipids into domains. Domain formation is observed even with rather short polyelectrolytes, suggesting that individual polyelectrolyte chains aggregate at the surface to form "superdomains". Overall, the polyelectrolyte bound at the lipid bilayer surface appears to lie flat along the surface and to be essentially immobilized through its multiple electrostatic contacts. 相似文献
16.
A novel continuum model is proposed to describe the deformations of a planar lipid bilayer suspended across a circular pore.
The model is derived within a new theoretical framework for smectic A liquid crystals in which the usual director n , which defines the average orientation of the molecules, is not constrained to be normal to the layers. The free energy
is defined by considering the elastic splay of the director, the bending and compression of the lipid bilayer, the cost of
tilting the director with respect to the layer normal, the surface tension, and the weak anchoring of the director. Variational
methods are used to derive the equilibrium equations and boundary conditions. The resulting boundary value problem is then
solved numerically to compute the fully nonlinear displacement of the layers and tilt of the lipid molecules. A parametric
study shows that an increase in surface tension produces a decrease in the deformation of the lipid bilayers while an opposite
effect is obtained when increasing the anchoring strength. 相似文献
17.
Coarse-grained simulations on interactions between spectrins and phase-separated lipid bilayers
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Xuegui Lin 《中国物理 B》2021,30(6):68701-068701
Spectrin, the principal protein of the cytoskeleton of erythrocyte, plays a crucial role in the stability and flexibility of the plasma membrane of erythrocyte. In this work, we investigate the interactions between spectrins and phase-separated lipid bilayers using coarse-grained molecular dynamics simulation. We focus on the preference of spectrins with different lipids, the effects of the anionic lipids and the residue mutation on the interactions between spectrins and the lipid bilayers. The results indicate that spectrins prefer to contact with phosphatidylethanolamine (PE) lipids rather than with phosphatidylcholine (PC) lipids, and tend to contact with the liquid-disordered (Ld) domains enriched in unsaturated PE. Additionally, the anionic lipids, which show specific interaction with the positively charged or polar amino acids on the surface of the spectrins, can enhance the attraction between the spectrins and lipid domains. The mutation leads to the decrease of the structural stability of spectrins and increases the curvature of the lipid bilayer. This work provides some theoretical insights into understanding the erythrocyte structure and the mechanism of some blood diseases. 相似文献
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