Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA.
Neuron. 2013 Oct 16;80(2):470-83. doi: 10.1016/j.neuron.2013.09.010. Epub 2013 Oct 10.
Synaptic vesicle fusion during neurotransmitter release is mediated by assembly of SNARE- and SM-protein complexes composed of syntaxin-1, SNAP-25, synaptobrevin-2/VAMP2, and Munc18-1. Current models suggest that SNARE-complex assembly catalyzes membrane fusion by pulling the transmembrane regions (TMRs) of SNARE proteins together, thus allowing their TMRs to form a fusion pore. These models are consistent with the requirement for TMRs in viral fusion proteins. However, the role of the SNARE TMRs in synaptic vesicle fusion has not yet been tested physiologically. Here, we examined whether synaptic SNAREs require TMRs for catalysis of synaptic vesicle fusion, which was monitored electrophysiologically at millisecond time resolution. Surprisingly, we find that both lipid-anchored syntaxin-1 and lipid-anchored synaptobrevin-2 lacking TMRs efficiently promoted spontaneous and Ca(2+)-triggered membrane fusion. Our data suggest that SNARE proteins function during fusion primarily as force generators, consistent with the notion that forcing lipid membranes close together suffices to induce membrane fusion.
神经递质释放过程中的突触囊泡融合是由 SNARE 和 SM 蛋白复合物的组装介导的，该复合物由突触融合蛋白 1（syntaxin-1）、突触相关蛋白 25（SNAP-25）、囊泡相关膜蛋白 2（synaptobrevin-2/VAMP2）和 Munc18-1 组成。目前的模型表明，SNARE 复合物的组装通过拉动 SNARE 蛋白的跨膜区域（TMRs）来促进膜融合，从而允许它们的 TMR 形成融合孔。这些模型与病毒融合蛋白中 TMR 的要求是一致的。然而，突触囊泡融合中的 SNARE TMR 的作用尚未在生理条件下进行测试。在这里，我们研究了突触 SNARE 是否需要 TMR 来催化突触囊泡融合，这是通过电生理学在毫秒时间分辨率下进行监测的。令人惊讶的是，我们发现，缺乏 TMR 的脂质锚定突触融合蛋白 1 和脂质锚定囊泡相关膜蛋白 2 都能有效地促进自发和 Ca(2+)触发的膜融合。我们的数据表明，SNARE 蛋白在融合过程中主要作为力发生器发挥作用，这与迫使脂质膜紧密结合足以诱导膜融合的观点一致。
