Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA.
Nat Struct Mol Biol. 2011 Jun 5;18(7):813-21. doi: 10.1038/nsmb.2075.
Synaptotagmin-1 is a Ca(2+) sensor that triggers synchronous neurotransmitter release. The first documented biochemical property of synaptotagmin-1 was its ability to aggregate membranes in response to Ca(2+). However, the mechanism and function of this process were poorly understood. Here we show that synaptotagmin-1-mediated vesicle aggregation is driven by trans interactions between synaptotagmin-1 molecules bound to different membranes. We found a strong correlation between the ability of Ca(2+)-bound synaptotagmin-1 to aggregate vesicles and to stimulate SNARE-mediated membrane fusion. Moreover, artificial aggregation of membranes-using non-synaptotagmin proteins-also efficiently promoted fusion of SNARE-bearing liposomes. Finally, using a modified fusion assay, we observed that synaptotagmin-1 drove the assembly of otherwise non-fusogenic individual t-SNARE proteins into fusion-competent heterodimers, independently of aggregation. Thus, membrane aggregation and t-SNARE assembly appear to be two key aspects of fusion reactions that are regulated by Ca(2+)-bound synaptotagmin-1 and catalyzed by SNAREs.
突触结合蛋白 1 是一种钙离子感受器，能引发神经递质同步释放。突触结合蛋白 1 的第一个被记录的生化特性是它能够在钙离子的响应下聚集膜。然而，这个过程的机制和功能仍不清楚。在这里，我们表明突触结合蛋白 1 介导的囊泡聚集是由结合在不同膜上的突触结合蛋白 1 分子之间的跨相互作用驱动的。我们发现，与 Ca(2+)-结合的突触结合蛋白 1 聚集囊泡的能力和刺激 SNARE 介导的膜融合之间存在很强的相关性。此外，使用非突触结合蛋白的人工膜聚集-也能有效地促进 SNARE 携带的脂质体融合。最后，通过改良的融合测定，我们观察到突触结合蛋白 1 驱动了原本不能融合的单个 t-SNARE 蛋白组装成融合能力的异二聚体，而无需聚集。因此，膜聚集和 t-SNARE 组装似乎是融合反应的两个关键方面，由 Ca(2+)-结合的突触结合蛋白 1 调节，并由 SNARE 催化。
