Molecular Dynamics Simulations of Sphingomyelin-Cholesterol Bilayers

Abstract

Sphingolipids are one of the major components in animal cell membranes. One type of sphingolipids is sphingomyelins which are abundant in myelin sheath surrounding nerve cell axons. The two common forms of sphingomyelin targeted in this research are palmitoylsphingomyelin (PSM) and stearoylsphingomyelin (SSM). Another bilayer component included in our membranes that has high affinity to sphingomyelins is cholesterol, which aids in maintaining membrane fluidity and structural integrity. Sphingomyelins and cholesterol make up a great part of highly dynamic membrane domains, termed lipid rafts. With that being said, this work tests the accuracy of molecular dynamics (MD) simulations with the CHARMM36 (C36) lipid force field for PSM and SSM, each SM bilayer has varying concentrations of cholesterol. Properties such as surface area per lipid, x-ray and neutron form factors, and chain deuterium order parameters are to be compared to those yielded from past experiments to prove C36's ability to correctly simulate the mixed SM-cholesterol lipid bilayers. Based on past studies on C36 lipid force field, we expect to see excellent agreement between experimental and MD simulation data for more complex mixtures of membranes that contain SM lipids.