Sec18 supports membrane fusion by promoting Sec17 membrane association.
Sec18 supports membrane fusion by promoting Sec17 membrane association.
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DOI：
10.1091/mbc.e22-07-0274
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发表时间：
2022-11-01
影响因子：
3.3
通讯作者：
Wickner, William
中科院分区：
文献类型：
--
作者：
Orr, Amy;Wickner, William
膜融合是由Sec17、Sec18和诱捕拉链驱动的。与SNARS结合的Sec17通过其膜近端N末端无极环区促进融合。在其膜末端，Sec17是Sec18的高亲和力受体。在距离聚变地点这么远的地方，尚不清楚Sec18如何帮助Sec17促进融合。我们现在报道，第18节，与三磷酸腺苷γS，降低了第17节的公里进行融合。C端和膜-远端Sec17突变L291A、L292A会降低Sec17与Sec18的亲和力。高水平的野生型Sec17或Sec17-L291AL292A在没有Sec18的情况下表现出相同的融合，但低水平的Sec17-L291AL292A对Sec18的融合促进作用远低于野生型Sec17。另一个突变体Sec17-F21SM22S降低了N-环去极化。只有非常高水平的突变蛋白支持融合，但Sec18仍然降低了Sec17-F21SM22S的表观融合Km。因此，Sec18通过Sec17刺激融合，并作用于Sec18和Sec17之间的界面。ATP作为配体激活Sec18进行依赖于Sec17的融合，但不需要ATP水解酶。即使没有陷阱，Sec18和Sec17也表现出与脂类的相互依赖的稳定结合，每个Sec18六角体结合了几个Sec17，解释了Sec17表面集中的簇的Sec18稳定如何降低了Sec17公里的装配与陷阱。SNARE复合体、Sec18、Sec17和脂质之间的每一种关联都有助于组装融合机制。
Membrane fusion is driven by Sec17, Sec18, and SNARE zippering. Sec17 bound to SNAREs promotes fusion through its membrane-proximal N-terminal apolar loop domain. At its membrane-distal end, Sec17 serves as a high-affinity receptor for Sec18. At that distance from the fusion site, it has been unclear how Sec18 can aid Sec17 to promote fusion. We now report that Sec18, with ATPγS, lowers the Km of Sec17 for fusion. A C-terminal and membrane-distal Sec17 mutation, L291A,L292A, diminishes Sec17 affinity for Sec18. High levels of wild-type Sec17 or Sec17-L291AL292A show equivalent fusion without Sec18, but Sec18 causes far less fusion enhancement with low levels of Sec17-L291AL292A than with wild-type Sec17. Another mutant, Sec17-F21SM22S, has reduced N-loop apolarity. Only very high levels of this mutant protein support fusion, but Sec18 still lowers the apparent fusion Km for Sec17-F21SM22S. Thus Sec18 stimulates fusion through Sec17 and acts at the well-described interface between Sec18 and Sec17. ATP acts as a ligand to activate Sec18 for Sec17-dependent fusion, but ATP hydrolysis is not required. Even without SNAREs, Sec18 and Sec17 exhibit interdependent stable association with lipids, with several Sec17 bound for each Sec18 hexamer, explaining how Sec18 stabilization of surface-concentrated clusters of Sec17 lowers the Sec17 Km for assembly with SNAREs. Each of the associations, between SNARE complex, Sec18, Sec17, and lipid, helps assemble the fusion machinery.