Zippering of SNARE complexes spanning docked membranes is essential for most intracellular fusion events. Here we explore how SNARE regulators operate on discrete zippering states. The formation of a metastable trans-complex, catalyzed by HOPS and its SM subunit Vps33, is followed by subsequent zippering transitions that increase the probability of fusion. Operating independently of Sec18 (NSF) catalysis, Sec17 (α-SNAP) either inhibits or stimulates SNARE-mediated fusion. If HOPS or Vps33 are absent, Sec17 inhibits fusion at an early stage. Thus, Vps33/HOPS promotes productive SNARE assembly in the presence of otherwise inhibitory Sec17. Once SNAREs are partially zipped, Sec17 promotes fusion in either the presence or absence of HOPS, but with faster kinetics when HOPS is absent, suggesting that ejection of the SM is a rate-limiting step.

对大多数细胞内融合事件而言，跨接膜的SNARE复合物的拉链拉紧是必不可少的。在这里，我们探讨了SNARE调节器如何在离散的拉链状态下工作。亚稳态反式的形成 在HOPS及其SM亚基Vps33催化下的复合物，随后进行了拉链过渡，从而增加了融合的可能性。独立于Sec18（NSF）催化运行，Sec17（α-SNAP）抑制或刺激SNARE介导的融合。如果不存在HOPS或Vps33，则Sec17会在早期抑制融合。因此，在存在抑制性Sec17的情况下，Vps33 / HOPS促进了高效的SNARE装配。SNARE部分压缩后，无论是否存在HOPS，Sec17都会促进融合，但是当缺少HOPS时，Sec17的动力学更快，这表明SM的弹出是一个限速步骤。