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. It binds acidic phospholipids with a specificity that requires the presence of both an acidic head group and a diacyl backbone. May play a role in dendrite formation by melanocytes. Binds 3 Ca(2+) ions per subunit. The ions are bound to the C2 domains. Homotetramer. The first C2 domain mediates Ca(2+)-dependent phospholipid binding. The second C2 domain mediates interaction with SV2A and probably with STN2. Belongs to the synaptotagmin family.