General model of phospholipid bilayers in fluid phase within the single chain mean field theory

TL;DR

This paper introduces a coarse-grained single chain mean field model for various phospholipids, accurately capturing their equilibrium and mechanical properties, and applicable to multilayer and interaction studies.

Contribution

A unified model for saturated and unsaturated phospholipids within the single chain mean field theory, accurately reproducing key bilayer properties with a single parameter set.

Findings

Model accurately predicts bilayer thickness and hydrophobic core dimensions.

Reproduces thermodynamical properties of unsaturated lipid bilayers.

Estimates free energies of bilayer deformations with reasonable accuracy.

Abstract

Coarse-grained model for saturated (DCPC, DLPC, DMPC, DPPC, DSPC) and unsaturated (POPC, DOPC) phospholipids is introduced within the Single Chain Mean Field theory. A single set of parameters adjusted for DMPC bilayers gives an adequate description of equilibrium and mechanical properties of a range of saturated lipid molecules that differ only in length of their hydrophobic tails and unsaturated (POPC, DOPC) phospholipids which have double bonds in the tails. A double bond is modeled with a fixed angle of 120 degrees, while the rest of the parameters are kept the same as saturated lipids. The thickness of the bilayer and its hydrophobic core, the compressibility and the equilibrium area per lipid correspond to experimentally measured values for each lipid, changing linearly with the length of the tail. The model for unsaturated phospholipids also fetches main thermodynamical properties of the bilayers. This model is used for an accurate estimation of the free energies of the compressed or stretched bilayers in stacks or multilayers and gives reasonable estimates for free energies. The proposed model may further be used for studies of mixtures of lipids, small molecule inclusions, interactions of bilayers with embedded proteins.