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 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.; (Microbial infection) Receptor for C.botulinum neurotoxin type B (BoNT/B, botB); interaction is improved in the presence of gangliosides. BoNT/B toxin binds to the membrane proximal vesicular domain of Syt1 (residues 32-51).; (Microbial infection) Receptor for C.botulinum neurotoxin type G (BoNT/G, botG); unlike the case with BoNT/B, interaction is not improved in the presence of gangliosides. BoNT/G toxin binds to the vesicular domain of Syt1 (residues 32-53).

> 85% as determined by SDS-PAGE.