A Comparison of Atomistic and Coarse-Grain MD Simulations Through Local Stress Analysis of Lipid Bilayers

Understanding the mechanical properties of lipid membranes is very important for many biological functions including membrane fusion, transport, and mechanosensation. One can characterize the mechanical state of a lipid bilayer through lateral stress or pressure profiles, which are uniquely sensitive to molecular features, obtained from molecular dynamic (MD) simulations. Lateral pressure profiles may be used to obtain various elastic constants by means of the integral moments. We analyze MD simulations of lipid bilayers of the commonly used phospholipids POPC and DPPC, and show that lateral pressure profiles are also largely sensitive to force-field parametrization in atomistic and coarse-grained models. We compare the atomistic force fields CHARMM36 and GROMOS 43A1-S3, as well as the coarse-grained force fields Martini, Polar Martini, Dry-Martini, and BMW-Martini. We further characterize the individual contributions of the interatomic potentials (i.e., VdW, coulomb, angles, et.) to the overall lateral pressure to better understand the internal balance of forces within the membrane. Our analysis shows an unexpected result that the lateral pressure profile from the atomistic CHARMM36 membrane closely resembles the profile of the solvent-free Dry-Martini force-field.