The Change Of Biomembrane Microstructure Induced By The Morphological Deformation:a Molecular Dynamics Simulation Study

Biomembrane is a kind of membrane that locate on the surface of cells and organelles, it separates the inner of cells from external environment and protect cells against outside interference. It can control the permeability of substances that are necessary for organisms (such as ion and glucose) and thereby maintain the biological metabolism of organisms.The main structure of the biomembrane is the lipid bilayer, which is composed of saturated phospholipids, unsaturated phospholipids and cholesterol. Recent studies show that a three-component membrane in a certain temperature will phase separate into liquid-ordered and liquid-disordered phase. While the membrane is in the state that two phases exist together, the distribution of two phases will be affected by external conditions.The deformation of the membrane could have a influence on the phase separation of the membrane. When a highly curved region is formed by the deformation of the membrane, lipid molecules would respond differently to the deformation because of the difference between them. The Liquid-disordered phase composed of unsaturated lipids with a smaller bending stiffness will accumulate to the curved area of the membrane while the Liquid-ordered phase composed of saturated lipids will aggregate to the planar region. On energetic grounds, this kind of lipid packing will reduce bending energy of the membrane.In addition, the curvature of the membrane will affect the sorting of proteins in the membrane. The protein would move to a new location in the process of redistribution. Because the protein is inserted into the membrane or adhere to the surface of the membrane, therefore, it is lipid molecules that relate to the movements of proteins.This article investigated the influence of the curvature on lateral organization of lipids and proteins in model membrane. For the complicated structure and dynamic nature of membranes, it is different to study with experimental methods. Molecular dynamics simulation is an effective method for these issues. At first, curved membranes were made and then to investigate the influence of the curvature on the lateral sorting of lipids and proteins. This paper mainly study the following issues:First, to test and verify the lipid packing of a three-component DPPC/DLiPC/cholesterol membrane using molecular dynamics simulation. Second, to study the phase separation of a curved membrane that do not phase separate in planar state. Third, to study the lateral organization of different kind of proteins that inserted in curved membranes. And finally, considering the interplay between lipids and proteins would affect the membrane, the curvatures of membranes were investigated.The following results were obtained through research:First, simulation results of the three-component membrane agree well with experiment results. Second, the phase separation was not observed in the curved membrane which do not phase separate in planar state. Third, the curvature of membranes could affect the distribution of proteins. The protein used in this study is cylindrical shape, so that the lateral organization is different from the conical or wedge-like proteins. During simulation, because of the difference between number densities of different regions of the membrane, cylindrical proteins tend to sort into curved region and then the shape of proteins would change to cone in order to steadily stay in curved area. However, another protein that do not change their shapes could not stay in the curved area steadily. Finally, we found that the aggregation of proteins to the curved region would increase the curvature of membranes.Through using molecular dynamics simulation to investigate the microstructure of the curved membrane, this study provide some theoretical opinions to related mechanisms of the lateral organization of lipids and proteins in deformed biomembranes.