Modeling Lipid–Sterol Bilayers: Applications to Structural Evolution, Lateral Diffusion, and Rafts

Abstract

This chapter describes the off-lattice models for lipid–cholesterol and lipid–lanosterol bilayers. The difference in behavior between the two sterols was modeled on the basis of their specific molecular characteristics and in terms of their differential interactions with lipid molecules. The Metropolis Monte Carlo method and the algorithm used in the MMC simulations of the model are analyzed. The simulated equilibrium phase diagrams for the lipid–cholesterol and the lipid–lanosterol membranes are shown. It is found that the small modification in the lipid–sterol interaction strength leads to considerable differences in the overall topologies of the two-phase diagrams. To characterize quantitatively, the differential effects of the two sterols on the physical properties of lipid–sterol bilayer membranes, the calculated conformational order parameter is presented. The lipid tracer diffusion coefficient in a model lipid–cholesterol binary mixture was calculated as a function of cholesterol concentration and temperature.