Synaptotagmin-1: A Multi-Functional Protein that Mediates Vesicle Docking, Priming, and Fusion

The fusion of secretory vesicles with the plasma membrane depends on the assembly of v-SNAREs (VAMP2/synaptobrevin2) and t-SNAREs (SNAP25/syntaxinl) into the SNARE complex. Vesicles go through several upstream steps, referred to as docking and priming, to gain fusion competence. The vesicular protein synaptotagmin-1 (Syt-1) is the principal Ca2+ sensor for fusion in several central nervous system neurons and neuroendocrine cells and part of the docking complex for secretory granules. Syt-1 binds to the acceptor complex such as synaxin1, SNAP-25 on the plasma membrane to facilitate secretory vesicle docking, and upon Ca2+-influx, it promotes vesicle fusion. This review assesses the role of the Syt-1 protein involved in the secretory vesicle docking, priming, and fusion.