J Phys Chem B. 2018 Dec 6;122(48):10834-10840. doi: 10.1021/acs.jpcb.8b09502. Epub 2018 Nov 19.
Neuronal transmitters are released from nerve terminals via the fusion of synaptic vesicles with the presynaptic membrane. Vesicles are attached to the membrane via the SNARE complex, comprising the vesicle associated protein synaptobrevin (Syb), the membrane associated protein syntaxin (Syx), and the cytosolic protein SNAP25, that together form a four-helical bundle. The full assembly of Syb onto the core SNARE bundle promotes vesicle fusion. We investigated SNARE assembly using a coarse-grained model of the SNARE complex that retains chemical specificity. Steered force-control simulations of SNARE unzippering were used to set up initial disassembled states of the SNARE complex. From these states, the assembly process was simulated. We find that if Syb is in helical form and proximal to the other helices, then the SNARE complex assembles rapidly, on a microsecond time-scale, which is well within in vivo synaptic vesicle fusion time scales. Assembly times grow exponentially with a separation distance between Syb and Syx C-termini. Our results indicate that for biologically relevant rapid assembly of the SNARE complex, Syb should be in helical form, and the SNARE constituent helices brought into proximity, possibly by an agent, such as a chaperone.
神经元递质通过突触小泡与突触前膜融合从神经末梢释放。囊泡通过 SNARE 复合物附着在膜上，该复合物由囊泡相关蛋白突触融合蛋白（Syb）、膜相关蛋白突触融合蛋白（Syx）和细胞质蛋白 SNAP25 组成，它们共同形成一个四螺旋束。Syb 完全组装到核心 SNARE 束上促进囊泡融合。我们使用保留化学特异性的 SNARE 复合物粗粒化模型研究了 SNARE 组装。使用 SNARE 解拉链的力控制模拟来设置 SNARE 复合物的初始解组装状态。从这些状态出发，模拟了组装过程。我们发现，如果 Syb 呈螺旋状且靠近其他螺旋，则 SNARE 复合物会在微秒时间尺度内快速组装，这远在体内突触囊泡融合时间尺度内。组装时间随 Syb 和 Syx C 末端之间的分离距离呈指数增长。我们的结果表明，对于生物相关的 SNARE 复合物的快速组装，Syb 应该呈螺旋状，并且 SNARE 组成螺旋通过某种介体（如伴侣蛋白）靠近。
