Calcium sensor that participates in triggering neurotransmitter release at the synapse. May have a regulatory role in the membrane interactions during trafficking of synaptic vesicles at the active zone of the synapse. It binds acidic phospholipids with a specificity that requires the presence of both an acidic head group and a diacyl backbone. A Ca2+-dependent interaction between synaptotagmin and putative receptors for activated protein kinase C has also been reported. It can bind to at least three additional proteins in a Ca2+-independent manner; these are neurexins, syntaxin and AP2. Plays a role in dendrite formation by melanocytes.