On the modulation of a high-enthalpy pretransition in binary mixtures of DMPC and DMPG by polar headgroup interaction

Anionic lipids are key components in the cell membranes. Many cell-regulatory and signaling mechanisms depend upon a complicated interplay between them and membrane-bound proteins. Phospholipid bilayers are commonly used as model systems in experimental or theoretical studies to gain insight into the structure and dynamics of biological membranes. We report here 200-ns-long MD simulations of pure (DMPC and DMPG) and mixed equimolar (DMPC/DMPG, DMPC/DMPS, and DMPC/DMPA) bilayers that each contain 256 lipids. The intra- and intermolecular interaction patterns in pure and mixed bilayers are analyzed and compared. The effect of monovalent ions (Na+) on the formation of salt-bridges is investigated. In particular, the number of Na(+)-mediated clusters in the presence of DMPS is higher than with DMPG and DMPA. We observe a preferential clustering of DMPS (and to some extent DMPA) lipids together rather than with DMPC molecules, which can explain the phase separation observed experimentally for DMPC/DMPS and DMPC/DMPA bilayers.

Section: Biophysical Propertiessupporting

confidence: 91%

Molecular Dynamics Simulations of Mixed Acidic/Zwitterionic Phospholipid Bilayers

Broemstrup

Reuter

2010

“…The onset temperature of the transition to the gel phase is --1 .50C higher for the SSV sample, indicating a destabilization of the liquid crystalline phase of DMPC-d54 due to the interaction with the glass surface. Heating the SSV sample after 3 h incubation at 1OOC now reproduces exactly the course of M, obtained for MLV upon heating (Bayerl et al, 1990a). These results suggest that the detachment of the bilayer from the glass surface occurs during the passage from the liquid crystalline to the gel state.…”

Section: Effects Of the Phase Transitionsupporting

confidence: 72%

“…Finally, the pellets were dried in a vacuum oven for 12 h at 80°C. The quality of surface smoothness and sphericity of the cleaned glass beads was inspected by freeze fracture electron microscopy according to procedures described elsewhere (Bayerl et al, 1988(Bayerl et al, , 1990a). The freeze fracture replicas exhibit smooth, structureless fracture faces indicating an essentially smooth surface of the glass beads.…”

Section: Preparation Of Spherical Supported Vesicle (Ssv) Samplesmentioning

confidence: 99%

Physical properties of single phospholipid bilayers adsorbed to micro glass beads. A new vesicular model system studied by 2H-nuclear magnetic resonance

Bayerl¹,

Bloom²

1990

Self Cite

434

389

Spherical supported vesicles (SSVs), a new model system consisting of single dimyristoyl phosphatidylcholine (DMPC) bilayers adsorbed to spherical glass beads with a narrow size distribution, were prepared at two different sizes (0.5 and 1.5 microns) and their physical properties were studied by deuterium nuclear magnetic resonance (2H-NMR). Such SSV samples can be prepared at any desired size between 0.3 and 10 microns. The 2H-NMR measurements provide evidence for a strong dependence of the spectra and the transverse relaxation times on the curvature of the SSVs in a diameter range between 0.5 and 1.5 microns. For larger SSVs (1.5 microns diameter) their powder spectra and their calculated oriented spectra are similar to those obtained for multilamellar dispersions of DMPC-d54. The lineshape of the smaller SSVs exhibits a temperature dependence which is not found in multilamellar samples. The SSVs are stable in the liquid crystalline phase over days but irreversibly change to multilamellar vesicles in the gel state. The average thickness of the water layer between the single bilayer and the glass bead surface was estimated by 1H-NMR to e 17 +/- 5 A.

“…4. However, in mixtures of DMPC and DMPG, a pretransition has been found that even displays a similar enthalpy to the main transition (Bayerl et al, 1990; cf. Fig.…”

Section: Discussionmentioning

confidence: 99%

A Model for the Lipid Pretransition: Coupling of Ripple Formation with the Chain-Melting Transition

Heimburg

2000

246

225

Below the thermotropic chain-melting transition, lipid membrane c(P) traces display a transition of low enthalpy called the lipid pretransition. It is linked to the formation of periodic membrane ripples. In the literature, these two transitions are usually regarded as independent events. Here, we present a model that is based on the assumption that both pretransition and main transition are caused by the same physical effect, namely chain melting. The splitting of the melting process into two peaks is found to be a consequence of the coupling of structural changes and chain-melting events. On the basis of this concept, we performed Monte Carlo simulations using two coupled monolayer lattices. In this calculation, ripples are considered to be one-dimensional defects of fluid lipid molecules. Because lipids change their area by approximately 24% upon melting, line defects are the only ones that are topologically possible in a triangular lattice. The formation of a fluid line defect on one monolayer leads to a local bending of the membrane. Geometric constraints result in the formation of periodic patterns of gel and fluid domains. This model, for the first time, is able to predict heat capacity profiles, which are comparable to the experimental c(P) traces that we obtained using calorimetry. The basic assumptions are in agreement with a large number of experimental observations.