Phase Transition of a DPPC Bilayer Induced by an External Surface Pressure: From Bilayer to Monolayer Behavior. A Molecular Dynamics Simulation Study (original) (raw)
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Effect of High Pressure on Fully Hydrated DPPC and POPC Bilayers
The Journal of Physical Chemistry B, 2011
Enhanced hydrostatic pressure can induce phase transitions in hydrated lipid bilayers especially those composed of saturated phospholipids. In this work, the phase behavior of fully hydrated DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and POPC (2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine) bilayers as a function of pressure up to 3000 atm has been examined in atomic detail on time scales of up to 1.0 μs, using the molecular dynamics simulation technique. DPPC bilayers formed a rippled gellike phase comprising a minor disordered fluid-like region and a major ordered gel-like region at 1000 atm, a partially interdigitated gel-like phase at 2000 atm, and a gel-like phase with most of the lipid acyl chains tilted with respect to the plane of the bilayer at 3000 atm. POPC bilayers formed a rippled gel-like phase at 1800, 2400, and 3000 atm. The phase behavior observed for both DPPC and POPC bilayers is in agreement with experiment. The simulations provide insight into the structural changes of DPPC and POPC bilayers as a function of pressure and demonstrate the ability to model biologically relevant lipid systems under high hydrostatic pressure.
Physical Review E, 2004
Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, we have studied, as a function of pressure, the much observed anomalous swelling regime in dimyristoyl-and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC, respectively. We have also reanalyzed data from a number of previously published experiments and have arrived at the following conclusions. ͑a͒ The power law behavior describing anomalous swelling is preserved in all PC bilayers up to a hydrostatic pressure of 240 MPa. ͑b͒ As a function of increasing pressure there is a concomitant decrease in the anomalous swelling of DMPC bilayers. ͑c͒ For PC lipids with hydrocarbon chains у13 carbons the theoretical unbinding transition temperature T Ã is coupled to the main gel-to-liquid crystalline transition temperature T M. ͑d͒ DLPC is intrinsically different from the other lipids studied in that its T Ã is not coupled to T M. ͑e͒ For DLPC bilayers we predict a hydrostatic pressure (Ͼ290 MPa) where unbinding may occur.
Biophysical Chemistry, 1982
A statistical thermodynamic model of phospholipid bilayers is devclopcd. In the model. ;I nexv concept of a cloxlg packed system is opplicd. i.e.. a system of hard cylinders of equal radii. the radius being a function of the avcragc number of .SWKIIP rotations in a hydrocarbon chain. Using this concept of a closely packed system. reasonable vaiucs arc ohtaincd for the chnngc in specific volume at :he order-disorder transition of lecithin bilaycrs. In addition to intcroctinns hctwccn the lipid matrix and water molecules. between the head groups themselves and bctwcen hydrocarbon chains. as wcli as the intramolecular cnerg?; nssociated with chain conformation. the Hamiltonian of the memhronc eho includes the cncrgy of the prcssurc field. Thus. the phase transition of phobphoiipid mernbrancs induced not only by tcmpcrature hut also hy hydrostatic prcssurc is dcscribcd by this model simultaneously. In accordance with the experimental results. a linear relationship is ohtaincd between the phase transition temperature and phase transition prcssurc. The other ca!culated phase trxxsition propcrtics of lecithin homologucc. cg.. changes in enthalpy. surface area. thickness and gurcc~w number per chain arc in ngrccmcnt with the availahlc experimental data. The ratio of kink to interstitial conduction of bilayers is also catimatcd.
Pressure−Area Isotherm of a Lipid Monolayer from Molecular Dynamics Simulations
Langmuir, 2007
We calculated the pressure-area isotherm of a dipalmitoyl-phosphatidylcholine (DPPC) lipid monolayer from molecular dynamics simulations using a coarse-grained molecular model. We characterized the monolayer structure, geometry, and phases directly from the simulations and compared the calculated isotherm to experiments. The calculated isotherm shows liquid-expanded and liquid-condensed phases and their coexistence plateau. At high pressure, the monolayer surface is rippled; upon further compression, the monolayer undergoes a collapse. We studied the effect of temperature and system size on the isotherm slope and phase coexistence region. Thermodynamic and dynamic properties of the monolayer phases were also investigated.
While the surface tension of a cell membrane, or a plasma membrane, regulates cell functions, little is known about its effect on the conformational changes of the lipid bilayer and hence the resulting changes in the cell membrane. To obtain some insights into the phase transition of the lipid bilayer as a function of surface tension, we used a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer as a model lipid bilayer and aquaporin (AqpZ), a transmembrane channel protein for water, as a model embedded protein. A coarse-grained molecular dynamics simulation was applied to illustrate the phase transition behavior of the pure DPPC bilayer and aquaporin-embedded DPPC bilayer under different surface tensions. It was shown that an increased surface tension reduced the phase transition temperature of the DPPC bilayer. As for the DPPC bilayer in gel form, no significant changes occurred in the structure of the bilayer in response to the surface tension. Once in a liquid crystal state, both the structure and properties of the DPPC bilayer, such as area per lipid, lipid order parameters, bilayer thickness and lateral diffusion coefficients, were responsive to the magnitude of surface tension in a linear way. The presence of aquaporin attenuated the compact alignment of the lipid bilayer, hindered the parallel movement, and thus made the DPPC bilayer less sensitive to the surface tension.
Langmuir, 1997
A series of molecular dynamics computer simulations have been carried out on fully hydrated liquid crystalline dipalmitoyl phosphatidylcholine (DPPC) bilayers at constant surface areas corresponding to 59.3, 62.9, 65.5, or 68.1 Å 2 /lipid, the range of values suggested by different experiments in different laboratories. Simulated quantities are compared with those from NMR (deuterium order parameters and contribution of molecular tilt to the order parameter), X-ray scattering (D-spacings and detailed density profiles), and partial molar volumes. The results strongly support the value of 62.9 Å 2 /DPPC recently proposed by Nagle et al. (Biophys. J. 1996, 70, 1419 and demonstrate the feasibility of a combined experimental, and simulation-based approach for determining membrane structure.
Molecular dynamics simulation of the fully hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer
2003
The structural properties of lipid bilayers in biological membranes are of great interest in biochemistry, biophysics, and medicine. The main goal of the present study was to use molecular dynamic (MD) techniques to investigate physical properties of the hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer. -- The bilayer model consists of 25 DPPC molecules per each monolayer and 44.8% water by total weight. A modified version of AMBER MD suit of programs with CHARMM22 force field for phospholipids was used in simulation. The isothermal-isobaric or NPT ensemble with a fully flexible simulation box in ROAR program was used in this study. Simulations were performed under different pressure and temperature conditions. -- According to experimental results, a liquid crystal phase (Lα) is expected with the DPPC bilayer simulated under 1 atm pressure and 323 K temperature conditions. However, area per lipid, bilayer thickness, chain tilt, and the order parameters resulting from the prese...
The Influence of 1-Alkanols and External Pressure on the Lateral Pressure Profiles of Lipid Bilayers
Biophysical Journal, 2008
The suggestion by Robert Cantor, that drug-induced pressure changes in lipid bilayers can change the conformational equilibrium between open and closed states of membrane proteins and thereby cause anesthesia, attracted much attention lately. Here, we studied the effect of both large external pressure and of 1-alkanols of different chain lengths-some of them anesthetics, others not-on the lateral pressure profiles across dimyristoylphosphatidylcholine (DMPC) bilayers by molecular dynamics simulations. For a pure DMPC bilayer, high pressure both reduced and broadened the tension at the interface hydrophobic/hydrophilic and diminished the repulsion between the phospholipid headgroups. Whereas the effect of ethanol on the lateral pressure profile was similar to the effect of a large external pressure on a DMPC bilayer, long-chain 1-alkanols significantly amplified local maxima and minima in the lateral pressure profile. For most 1-alkanols, external pressure had moderate effects and did not reverse the changes 1-alkanols exerted on the pressure profile. Nevertheless, assuming the bent helix model as a simple geometric model for the transmembrane region of a membrane protein, protein conformational equilibria were shifted in opposite directions by addition of 1-alkanols and additional application of external pressure.
Biophysical Journal, 1997
Molecular dynamics simulations of 500 ps were performed on a system consisting of a bilayer of 64 molecules of the lipid dipalmitoylphosphatidylcholine and 23 water molecules per lipid at an isotropic pressure of 1 atm and 50 degrees C. Special attention was devoted to reproduce the correct density of the lipid, because this quantity is known experimentally with a precision better than 1%. For this purpose, the Lennard-Jones parameters of the hydrocarbon chains were adjusted by simulating a system consisting of 128 pentadecane molecules and varying the Lennard-Jones parameters until the experimental density and heat of vaporization were obtained. With these parameters the lipid density resulted in perfect agreement with the experimental density. The orientational order parameter of the hydrocarbon chains agreed perfectly well with the experimental values, which, because of its correlation with the area per lipid, makes it possible to give a proper estimate of the area per lipid of 0.61 +/- 0.01 nm2.