Relationship Of The Structures And Properties Of Biomembrane: A Simulation Study

The relationship of the structures and properties of biomembrane, which is an important component of cell, is very important for development and improvement of cell biology. It is introduced the component, structure, and function of biomembrane. And, the research of the structure and function of bilayer and properties of phospholipids and proteins of membrane, which have been studied by many scientists, are also presented in the paper. It is needed to develop deeply due to the lack of work of biomembrane. By using the dissipative particle dynamics method, the dynamical property and microstructure are studied in molecular details and some results are found.The kinetic process of collision-driven solute transfer in an aqueous phase in which micelles are used as solute carriers is investigated by dissipative particle dynamics simulations. It is showed that in the transfer process of hydrophobic solute molecules, how the solute molecules are transferred through collision and fusion between micelle and bilayer and what factors affect the whole process. The simulation results indicate that, after a stage of intermittent collision between two neighboring aggregates, the fusion happens and the solute molecules transfer from the micelle to bilayer and diffuse. There are roughly three sequential events in a coalescence stage:(1) molecular contact, (2) neck formation, and (3) neck growth. It is found that there are two rate-limiting steps in the whole process of solute transfer, i.e., the break of the water film between two neighboring aggregates and the nucleation of a pore between two surfactant films. The effects of the collision velocity, the surface tension, the repulsive interaction between the surfactant films of the colliding aggregates, as well as the steric repulsion are examined. The simulation results show that the depletion force plays an important role during the coalescence stage, while the initial collision velocity basically does not change the fusion ratio. The results also demonstrate that the stronger of the surface tension facilitates the formation of the pores and increase of the fusion ratio. The effect of interaction between the colliding aggregates and the steric repulsion change the energy barrier and the fusion ratio.It is known that the archaebacterial cell membrane, which is formed by the bolaform phospholipids, is thermal stability at high temperature. For example, the thermoacidophilic archaebacterium Sulfolobus acidocaldarius can grow in hot springs at 65-80℃and live in acidic environments (pH 2-3). However, the origin of its unusual thermal stability remains unclear. In this work, using a vesicle as a model, the thermal stability and rupture of archaebacterial cell membrane are studied by using dissipative particle dynamics method. The structure-property relationship of monolayer membrane formed by bolaform lipids is found by comparing it with that of bilayer membrane formed by monopolar lipids. The origin of the unusually thermal stability of archaebacterial cell and the mechanism for its rupture are presented in molecular details.According to the structure and property of a kind of membrane protein, the mechanosensitive channel of small conductance (MscS), a coarse-grained model is proposed. The basic structure of the MscS is preserved when the protein is coarse grained. For the coarse-grained model, the channels show two different states, namely the open and closed states, depending on the model parameters in the dissipative particle dynamics simulations. Under the same membrane tension, the state of the ion channel is found to be critically determined by the protein structure, especially the length of three transmembrane a-helices. It is also found that for the protein with certain size, the gating transition occurs when the membrane tension is applied, resembling in a real mechanosensitive channel.The cluster formation of anchored proteins in a membrane has been studied in this work by dissipative particle dynamics simulation. The rate and extent of clustering is found to be dependent on the hydrophobic length of the anchored proteins embedded in the membrane. The cluster formation mechanism of anchored proteins in our work is ascribed to the different local perturbations on the upper and lower monolayers of the membrane and the intermonolayer coupling. Simulation results demonstrate that only when the hydrophobic depth of anchored proteins is larger than half the membrane thickness, the structure of the lower monolayer can be significantly deformed. Moreover, studies on the local structures of membranes indicate weak perturbation of bilayer thickness for a shallowly inserted protein, whereas there is significant perturbation for a more deeply inserted protein. Finally, in this study we addressed the difference of cluster formation mechanisms between anchored proteins and transmembrane proteins.