SIMULATION OF THE SPONTANEOUS FORMATION OF A SMALL DPPC VESICLE

摘要

@@Solutions of lipid molecules exhibit a large variety of aggregation states. One of these possible aggregation states is vesicular, in which the lipids form a spherically closed bilayer, i.e., a vesicle or a liposome. Such vesicles are important model systems for biological membranes[l-3]. Previous simulation studies using simplified models have shown that, under appropriate conditions, small vesicles can be formed spontaneously from disordered solutions of amphiphiles. For examples, Marrink and Mark used coarse grained molecular dynamics simulation to study the aggregation of DPPC lipid into small unilamellar vesicle. They observed bicelles and cuplike vesicles, and especially hemifused vesicle at higher lipid concentration[1]. Here, we simulate the Selfassembly of a small vesicle from a disordered solution of dipalmitoylphosphatidylcholine(DPPC) in water in atomistic details. In this study, Figure 1 shows a series of snapshots illustrating the evolution of the DPPC solutions (DPPC : water= 1:92). The initial stages of the aggregation process are very rapid. From random starting solution to micellar-like structures only takes Ins. Then these micelles aggregate into large micelles, as shown in Figure 1C. The increase in the curvature of these large micelles lead to the overall aggregate adopting a vesicle-like shape. This is already visible within 39ns (Figure 1D), we found that the orientations of the headgroups with respect to each other are similar in the inner and outer leaflets but the tails of lipids in the outer leaflet lie more along the local bilayer normal than the tails in the inner leaflet.