Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA.
EMBO J. 2010 Jun 16;29(12):1948-60. doi: 10.1038/emboj.2010.97. Epub 2010 May 14.
SNARE-dependent membrane fusion requires the disassembly of cis-SNARE complexes (formed by SNAREs anchored to one membrane) followed by the assembly of trans-SNARE complexes (SNAREs anchored to two apposed membranes). Although SNARE complex disassembly and assembly might be thought to be opposing reactions, the proteins promoting disassembly (Sec17p/Sec18p) and assembly (the HOPS complex) work synergistically to support fusion. We now report that trans-SNARE complexes formed during vacuole fusion are largely associated with Sec17p. Using a reconstituted proteoliposome fusion system, we show that trans-SNARE complex, like cis-SNARE complex, is sensitive to Sec17p/Sec18p mediated disassembly. Strikingly, HOPS inhibits the disassembly of SNARE complexes in the trans-, but not in the cis-, configuration. This selective HOPS preservation of trans-SNARE complexes requires HOPS:SNARE recognition and is lost when the apposed bilayers are dissolved in Triton X-100; it is also observed during fusion of isolated vacuoles. HOPS thus directs the Sec17p/Sec18p chaperone system to maximize functional trans-SNARE complex for membrane fusion, a new role of tethering factors during membrane traffic.
SNARE 依赖性膜融合需要顺式 SNARE 复合物（由锚定在一个膜上的 SNARE 组成）的解组装，然后是反式 SNARE 复合物（锚定在两个相邻膜上的 SNARE）的组装。尽管 SNARE 复合物的解组装和组装可能被认为是相反的反应，但促进解组装的蛋白质（Sec17p/Sec18p）和组装（HOPS 复合物）协同作用以支持融合。我们现在报告说，在液泡融合过程中形成的反式 SNARE 复合物在很大程度上与 Sec17p 相关。使用重建的脂蛋白体融合系统，我们表明反式 SNARE 复合物与顺式 SNARE 复合物一样，对 Sec17p/Sec18p 介导的解组装敏感。引人注目的是，HOPS 抑制 SNARE 复合物在反式而非顺式构型中的解组装。这种选择性的 HOPS 对反式 SNARE 复合物的保留需要 HOPS：SNARE 识别，并且当相邻的双层在 Triton X-100 中溶解时会丢失；在分离的液泡融合过程中也观察到了这种情况。因此，HOPS 指导 Sec17p/Sec18p 伴侣系统将功能性反式 SNARE 复合物最大化用于膜融合，这是膜运输过程中 tethering 因子的新作用。
