Role of synaptotagmin in Ca2+-triggered exocytosis

The Ca2+-binding synaptic-vesicle protein synaptotagrnin I has attracted considerable interest as a potential Ca2+ sensor that regulates exocytosis from neurons and neuroendocrine cells. Recent Studies have shed new light on the structure, biochemical/biophysical properties and function of synaptotagmin, and the emerging view is that it plays an important role in both exocytosis and endocytosis. At least a dozen additional isoforms exist, some of which are expressed outside of the nervous system, suggesting that synaptotagmins might regulate membrane traffic in a variety of cell types. Here we provide an overview of the members of this gene family, with particular emphasis on the question of whether and how synaptotagmin I functions during the final stages of membrane fusion: does it regulate the Ca2+ triggered opening and dilation of fusion pores?.