Dissipative particle dynamics of tension-induced membrane fusion

Recent studies of tension-induced membrane fusion using dissipative particle dynamics (DPD) simulations are briefly reviewed. The stochastic nature of the fusion process makes it necessary to simulate a large number of fusion attempts in order to obtain reliable fusion statistics and to extract meaningful values for the fusion probability and the average fusion times. All successful fusion events follow the same pathway. In this fusion pathway, configurations of individual lipids play an important role. Fusion starts with individual lipids assuming a splayed tail configuration with one tail inserted into each membrane. In order to determine the corresponding energy barrier, we measure the average work to displace one lipid molecule from one bilayer to the other. This energy barrier is found to depend strongly on a certain DPD parameter, and, thus, can be adjusted in the simulations. Overall, three sub-processes have been identified in the fusion pathway. Their energy barriers are estimated to lie in the range 8-15kBT. The fusion probability is found to possess a maximum at intermediate tension values. As one decreases the tension, the fusion probability seems to vanish before the tensionless membrane state is attained. This would imply that the tension has to exceed a certain threshold value in order to induce fusion.