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 (By similarity). May play a role in regulating the secretion of hormones relevant to the reproduction and egg-laying of female geese (PubMed:25146222). Binds 3 Ca(2+) ions per subunit. The ions are bound to the C2 domains. Homotetramer (Probable). Synaptic vesicles and chromaffin granules. Expressed during egg-laying cycle in the hypothalamus and pituitary. Expression increases from the pre-laying period to the peak laying period reaching its highest level in the peak laying period and then decreases in the ceased period (PubMed:25146222). Expression is up-regulated in the pituitary gland during egg-laying period and down-regulated during ceased period (PubMed:25049869). 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.