v-SNARE transmembrane domains function as catalysts for vesicle fusion
v-SNARE transmembrane domains function as catalysts for vesicle fusion
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DOI：
10.7554/elife.17571
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发表时间：
2016-06-25
期刊：
影响因子：
7.7
通讯作者：
Bruns, Dieter
中科院分区：
文献类型：
--
作者：
Dhara, Madhurima;Yarzagaray, Antonio;Bruns, Dieter
囊泡融合是由SNARE蛋白在对立膜之间的组装介导的，但目前尚不清楚SNARE蛋白的跨膜结构域（TMDs）是否具有机制功能，而不仅仅是将产生力的SNAREpin被动锚定在融合膜上。在这里，我们发现synaptobrevin-2 TMD的构象灵活性对于有效的ca2触发的胞吐至关重要，并积极促进膜融合和融合孔扩张。具体来说，在跨越囊泡外层小叶的TMD区域内引入稳定螺旋的亮氨酸残基会严重损害胞吐作用并减缓融合孔扩张。相比之下，增加TMD中螺旋不稳定、b支化缬氨酸或异亮氨酸残基的数量可以恢复正常分泌，但会加速融合孔扩张，超过野生型蛋白的速度。这些观察结果证明，synaptobrevin-2 TMD通过其结构灵活性催化融合过程，积极设定融合孔扩张的速度。
Vesicle fusion is mediated by an assembly of SNARE proteins between opposing membranes, but it is unknown whether transmembrane domains (TMDs) of SNARE proteins serve mechanistic functions that go beyond passive anchoring of the force-generating SNAREpin to the fusing membranes. Here, we show that conformational flexibility of synaptobrevin-2 TMD is essential for efficient Ca2-triggered exocytosis and actively promotes membrane fusion as well as fusion pore expansion. Specifically, the introduction of helix-stabilizing leucine residues within the TMD region spanning the vesicle's outer leaflet strongly impairs exocytosis and decelerates fusion pore dilation. In contrast, increasing the number of helix-destabilizing, B-branched valine or isoleucine residues within the TMD restores normal secretion but accelerates fusion pore expansion beyond the rate found for the wildtype protein. These observations provide evidence that the synaptobrevin-2 TMD catalyzes the fusion process by its structural flexibility, actively setting the pace of fusion pore expansion.