Calcium sensor that participates in triggering neurotransmitter release at the synapse (By similarity). May have a regulatory role in the membrane interactions during trafficking of synaptic vesicles at the active zone of the synapse (By similarity). It binds acidic phospholipids with a specificity that requires the presence of both an acidic head group and a diacyl backbone. A Ca(2+)-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 Ca(2+)-independent manner; these are neurexins, syntaxin and AP2. Plays a role in dendrite formation by melanocytes (By similarity). Binds 3 Ca(2+) ions per subunit. The ions are bound to the C2 domains. Homotetramer (Probable). Interacts with SCAMP5 (By similarity). Interacts with STON2 (By similarity). Forms a complex with SV2B, syntaxin 1 and SNAP25 (By similarity). Interacts with SV2A, SV2B and SV2C (By similarity). Interacts with RIMS1 (By similarity). Interacts with PRRT2 (By similarity). Interacts with DNAJC5 in a phosphorylation-dependent manner (By similarity). Interacts (via N-terminus) with RAB3A (By similarity). Interacts with SYT12 (By similarity). Interacts with calmodulin (By similarity). The first C2 domain mediates Ca(2+)-dependent phospholipid binding. The second C2 domain mediates interaction with SV2A and probably with STN2. Glycosylated. Belongs to the synaptotagmin family.