CONICET | Buscador de Institutos y Recursos Humanos

Cell membranes contain hundreds of lipid species and proteins arranged in heterogeneous domains. Nowadays it is known that this compositional and morphological heterogeneity is central to their functions of substance trafficking and protein interactions. It is therefore necessary to rationalize how the lateral pressure boundary conditions affect the structure, ordering and dynamics of the lipid domains. We performed Molecular Dynamics simulations (MD) on hydrated lipid bilayers of DPPC in Gel(G, T=22°C) and Liquid-crystalline(LC, T=50°C) phases, at several lateral pressure values (ensemble of constant surface tension, ST) to evaluate its influence in the structural and ordering properties. For both phases the MD were performed over a bilayer of 480 lipids, at ST values of 14 and 28 dyn/cm, being the former that which reproduces the experimental NMR Deuterium order parameter profiles of the LC-phase. One of the relevant structural properties is the area per lipid: Are [G,ST=14dyn/cm]=(44.7+/- 0.4)Å^2; Area[G,ST=28dyn/cm]=(48.3+/-0.2)Å^2; Area[LC,ST=14dyn/cm]=(61.5 +/-0.7)Å^2; Area[LC,ST=28dyn/cm]=(75.0+/-0.3)Å^2. The results show that the LC-phase is much more sensible to the change in lateral pressure than the ordered G-phase. The hydration of the lipid polar groups is known as a relevant contribution to the interface energetic. The number of H-bonds of water to the carbonyl O per lipid are: HB[G,ST=14dyn/cm]=5.14; HB[G,ST=28dyn/cm]=5.19; HB[LC,ST=14dyn/cm]=5.69; HB[LC,ST=28dyn/cm]=6.09. It is shown that the larger change is for the LC-phase. The change in the LC-phase area explains this behavior and also that the number of water whose orientational potential is perturbed by the interface is more sensitive for this case. We have also analyzed the changes in the order parameter profiles, the number of water that bridged among the lipids, and the lateral pressure profiles across the bilayer to untangle the contributions from different lipid regions.