Gao Lianghui, Lipowsky Reinhard, Shillcock Julian
Department of Chemistry, Beijing Normal University, Beijing 100875, China.
Max Planck Institute of Colloids and Interfaces, Potsdam 14424, Germany.
Soft Matter. 2008 May 14;4(6):1208-1214. doi: 10.1039/b801407h.
The dynamics of tension-induced fusion of two vesicles is studied using dissipative particle dynamics (DPD) simulations. The vesicle membranes use an improved DPD parameter set that results in their sustaining only a 10-30% relative area stretch before rupturing on the microsecond timescale of the simulations. Two distinct fusion pathways are observed depending on the initial vesicle tensions. In pathway I, at low membrane tension, a flattened adhesion zone is formed between the vesicles, and one vesicle subsequently ruptures in this contact zone to form a hemifusion state. This state is unstable and eventually opens a pore to complete the fusion process. In pathway II, at higher tension, a stalk is formed during the fusion process that is then transformed by transmembrane pore formation into a fusion pore. Whereas the latter pathway II resembles stalk pathways as observed in other simulation studies, fusion pathway I, which does not involve any stalk formation, has not been described previously to the best of our knowledge. A statistical analysis of the various processes shows that fusion is the dominant pathway for releasing the tension of the vesicles. The functional dependence of the observed fusion time on membrane tension implies that the fusion process is completed by overcoming two energy barriers with scales of 13kBT and 11kBT. The fusion pore radius as a function of time has also been extracted from the simulations, and provides a quantitative measure of the fusion dynamics which are in agreement with recent experiments.
使用耗散粒子动力学（DPD）模拟研究了张力诱导的两个囊泡融合的动力学。囊泡膜使用了改进的DPD参数集，这使得它们在模拟的微秒时间尺度上破裂之前仅能承受10%-30%的相对面积拉伸。根据初始囊泡张力观察到两种不同的融合途径。在途径I中，在低膜张力下，囊泡之间形成一个扁平的粘附区，随后一个囊泡在这个接触区破裂形成半融合状态。这种状态是不稳定的，最终会打开一个孔以完成融合过程。在途径II中，在较高张力下，融合过程中形成一个柄，然后通过跨膜孔的形成转化为融合孔。虽然后一种途径II类似于其他模拟研究中观察到的柄途径，但据我们所知，不涉及任何柄形成的融合途径I以前尚未被描述过。对各种过程的统计分析表明，融合是释放囊泡张力的主要途径。观察到的融合时间对膜张力的函数依赖性意味着融合过程是通过克服两个尺度分别为13kBT和11kBT的能量障碍来完成的。还从模拟中提取了融合孔半径作为时间的函数，并提供了与最近实验一致的融合动力学的定量测量。
