A modified BMW-MARTINI coarse grained model of POPE and POPC is capable of reproducing the mechanical properties of pure and mixed monolayers

Abstract

Biological membranes consist in a lipid bilayer with selective permeability for different chemical species. Ions have high energetic barrier to be transferred from water into the membrane. However, voltageinduced lipid channels can allow current transmission trough membranes, in the absence of protein channels. Such studies are usually done in a bilayer model system prepared in the presence of n-decane as a lipid solvent. Our aim is to simulate such membranes and later subject them to external electric fields. Coarse grained (CG) models are highly useful and reliable tools for the characterization of lipid systems. BMW-MARTINI is a molecular CG model with a water molecule with three charge sites that reproduces the experimental dipole potential at the membrane-water interface. BMW-martini force-field failed to reproduce the experimental surface pressure () – mean molecular area (A) compression isotherms of pure and mixed POPE and POPC Langmuir films (LF). However, LF with similar compositions with or without n-decane, could be successfully simulated by molecular dynamics after introducing modifications in the force field. The self-assembly process of a LF was analyzed to determine whether n-decane was excluded from the monolayer to the lipid- water or to the lipid-air interface. Finally, MD simulations of mixed POPE-POPC bilayers with charge imbalance were performed.