Data for Capturing Phase Behavior of Ternary Lipid Mixtrures with a Refined Martini Coarse-Grained Force Field (2018)
Whether lipid rafts are present in the membranes of living cells remains hotly disputed despite their incontrovertible existence in liposomes at 298 K. In attempts to resolve this debate, molecular dynamics (MD) simulations have been extensively used to study lipid phase separation at high resolution. However, computation has been of limited utility in this respect because the experimental distributions of phases in lamellar lipid mixtures are poorly reproduced by simulations. In particular, all-atom (AA) approaches suffer from restrictions on accessible time scales and system sizes whereas the more efficient coarse-grained (CG) force fields remain insufficiently accurate to achieve correspondence with experiment. In this work, we refine the CG Martini parameters for the high- and low-melting temperature (Tm) lipids 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC). Our approach involves the modification of bonded Martini parameters based on fitting to atomistic simulations conducted with the CHARMM36 lipid force field. The resulting CG parameters reproduce experimental structural and thermodynamic properties of homogeneous lipid membranes while concurrently improving simulation fidelity to experimental phase diagrams of DPPC, DOPC, and cholesterol lipid mixtures. Importantly, the refined parameters provide much better phase accuracy for regions near the critical point that mimic the lipid concentrations under physiological conditions.
Here we provide two equilibrated membrane structures (pdb format) and images (tga format) for each of the "extensible" and "optimal" parameters. The first structure in each case is a lipid mixture that is separated into disordered and ordered regions (40% DPPC, 30% DOPC, 30% CHOL). The second structure is a lipid mixture separated into disordered regions and ordered regions that exhibit some partial gel features (70% DPPC, 20% DOPC, 10% CHOL).
We also provide force-field parameter files -- there are parameters for high- and low-melting temperature lipids in the "extensible" and "optimal" cases.