Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, United States.
Elife. 2021 Oct 26;10:e73240. doi: 10.7554/eLife.73240.
Yeast vacuolar membrane fusion has been reconstituted with R, Qa, Qb, and Qc-family SNAREs, Sec17/αSNAP, Sec18/NSF, and the hexameric HOPS complex. HOPS tethers membranes and catalyzes SNARE assembly into RQaQbQc -complexes which zipper through their SNARE domains to promote fusion. Previously, we demonstrated that Sec17 and Sec18 can bypass the requirement of complete zippering for fusion (Song et al., 2021), but it has been unclear whether this activity of Sec17 and Sec18 is directly coupled to HOPS. HOPS can be replaced for fusion by a synthetic tether when the three Q-SNAREs are pre-assembled. We now report that fusion intermediates with arrested SNARE zippering, formed with a synthetic tether but without HOPS, support Sec17/Sec18-triggered fusion. This zippering-bypass fusion is thus a direct result of Sec17 and Sec18 interactions: with each other, with the platform of partially zippered SNAREs, and with the apposed tethered membranes. As these fusion elements are shared among all exocytic and endocytic traffic, Sec17 and Sec18 may have a general role in directly promoting fusion.
酵母液泡膜融合已通过 R、Qa、Qb 和 Qc 家族 SNARE、Sec17/αSNAP、Sec18/NSF 和六聚体 HOPS 复合物进行了重建。HOPS 将膜连接起来，并催化 SNARE 组装成 RQaQbQc 复合物，该复合物通过 SNARE 结构域拉链促进融合。以前，我们证明了 Sec17 和 Sec18 可以绕过完全拉链融合的要求（Song 等人，2021 年），但尚不清楚 Sec17 和 Sec18 的这种活性是否直接与 HOPS 相关联。当三个 Q-SNARE 预先组装时，HOPS 可以被合成的系绳取代以促进融合。我们现在报告说，形成具有合成系绳但没有 HOPS 的融合中间产物，支持 Sec17/Sec18 触发的融合。因此，这种绕过拉链的融合是 Sec17 和 Sec18 相互作用的直接结果：彼此之间，与部分拉链 SNARE 的平台之间，以及与对接的系绳膜之间。由于这些融合元素在所有胞吐和胞吞运输中共享，Sec17 和 Sec18 可能在直接促进融合方面发挥一般作用。
