Stereospecific Interactions of Cholesterol in a Model Cell Membrane: Implications for the Membrane Dipole Potential.

Cholesterol is a major constituent of the plasma membrane in higher order eukaryotes. The effect of cholesterol on the structure and organisation of cell membranes has been studied extensively by both experimental and computational means. In recent years, a wealth of data has been accumulated illustrating how subtle differences in the structure of cholesterol equate to considerable changes in the physical properties of the membrane. The effect of cholesterol stereoisomers, in particular, has been established, identifying a direct link with the activity of specific membrane proteins. In this study, we perform extensive molecular dynamics simulations of phospholipid bilayers containing three isomers of cholesterol, the native form (nat-cholesterol), the enantiomer of the native form (ent-cholesterol), and an epimer of cholesterol that differs by the orientation of the polar hydroxyl group (epi-cholesterol). Based on these simulations, an atomic-level description of the stereospecific cholesterol-phospholipid interactions is provided, establishing a potential mechanism for the perturbation of membrane properties, specifically the membrane dipole potential.