Influence of Cholesterol on Phospholipid Bilayer Structure and Dynamics

In this study, the influence of cholesterol on lipid bilayers is investigated by changing phospholipid headgroup, cholesterol concentration, chain saturation, and temperature. Molecular dynamics (MD) simulations were used to characterize bilayers containing phosphatidylcholine (PC) head groups with either fully saturated dimyristoyl (DM) or monounsaturated dioleoyl (DO) acyl chains and cholesterol concentrations ranging from S to 50%. To further explore the effects of cholesterol on bilayers with different head groups, we also performed MD simulations of bilayer systems having 15% cholesterol with phosphatidic acid (PA), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylinositol (PI), and phosphatidylserine (PS), each having DM chains and at a temperature above the solid gel phase transition. Additionally, bilayers of DMPA, DMPE, and DMPS with 15% cholesterol were simulated at temperatures below the solid gel phase transition temperatures. Compared to membranes without cholesterol, cholesterol in the model bilayers increases chain order in bilayers with the highest order in the liquid ordered and solid gel phases. Head group properties and acyl chain saturation are also found to critically impact bilayer dynamics, largely through the formation of hydrogen bonds between membrane components. These results provide a better understanding of the basic characteristics on structure and dynamics of cholesterol-containing membranes by revealing molecular details of interactions between cholesterol and phospholipids as well as add to the library of simulation data necessary for the MD community to accurately represent relevant models of atomic-scale systems.