Physical mechanism analysis of cholesterol concentration effect on asymmetric phospholipid membrane

Abstract

Cell membrane is a multi-component complex system containing large number of membrane proteins and various types of sterols, so its properties are closely relevant to the interaction of sterols with phospholipid membranes. In this paper, we use the molecular dynamics method to investigate the effect of cholesterol concentration on asymmetric phospholipid system. To describe the membrane with the complex lipid components, we employ the coarse-grained model and choose three types of saturated phospholipids, DPPC, DPPE and DPPS, as the membrane components. The different concentrations of cholesterol are represented by five systems, so different physical influences on asymmetric phospholipid membrane can be exhibited. After enough time of the molecular simulation, the structural properties of the membrane, such as lipid accumulation, lipid tail sequence, lipid diffusion and cholesterol turnover, are obtained. The analysis on the total energy of the system, the L-J and electrostatic interaction between cholesterol molecules and phospholipid membrane system shows that the effect of cholesterol concentration on asymmetric phospholipid membrane is through changing the fluidity of asymmetric phospholipid membrane. Meanwhile, the distribution of cholesterol molecules in phospholipid membrane shows that most of them are concentrated in the inner side of phospholipid membrane, which also leads to the increase in tail order parameter and the thickness of phospholipid membrane. At the same time, we take into account the stress of cholesterol molecules to analyze the turnover of cholesterol molecules in different concentrations in the phospholipid membrane, and find that there is no obvious law of the stress on cholesterol molecules at different concentrations. Therefore, the turnover frequency of cholesterol molecules is mainly due to the stronger fluidity of the phospholipid membrane when the concentration of cholesterol increases. Our research can provide some help for a better understanding of the basic characteristics of the structure and kinetics of membranes containing cholesterol.