Exhibits calcium-dependent phospholipid and inositol polyphosphate binding properties (PubMed:7961887). May have a regulatory role in the membrane interactions during trafficking of synaptic vesicles at the active zone of the synapse (PubMed:7961887). Plays a role in dendrite formation by melanocytes (By similarity). (Microbial infection) Receptor for C.botulinum neurotoxin type B (BoNT/B, botB); interaction is improved in the presence of gangliosides (PubMed:14504267). The toxin binds via the vesicular domain (residues 47-60) (PubMed:14504267, PubMed:17167418, PubMed:23807078). (Microbial infection) Receptor for C.botulinum neurotoxin type G (BoNT/G, botG); gangliosides are not required for (or only very slightly improve) binding to a membrane-anchored receptor fragment (PubMed:20219474). The toxin binds via the vesicular domain (residues 47-55) (PubMed:20219474). 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). Interacts with PRRT2 (PubMed:27052163). (Microbial infection) Interacts with C.botulinum neurotoxin type B (BoNT/B, botB). (Microbial infection) Interacts with C.botulinum neurotoxin type G (BoNT/G, botG). The first C2 domain mediates Ca(2+)-dependent phospholipid binding (PubMed:7961887). The second C2 domain mediates interaction with Stonin 2. The second C2 domain mediates phospholipid and inositol polyphosphate binding in a calcium-independent manner (PubMed:7961887). (Microbial infection) Binding to BoNT/B induces formation of an alpha-helix in the membrane-proximal extracytoplasmic domain (PubMed:17167418, PubMed:23807078). Belongs to the synaptotagmin family.