Plays a role in the control of regulated secretion in neural and endocrine cells, enhancing selectively low-frequency neurotransmission. Positively regulates vesicle fusion by maintaining the readily releasable pool of secretory vesicles. (Microbial infection) Receptor for C.botulinum neurotoxin type A (BoNT/A, botA); the toxin probably binds via extracellular loop 4 (PubMed:27313224). Recognition by BoNT/A relies on both protein-protein and protein-N-glycosylation; glycosylation of Asn-559 increases its affinity for BoNT/A (PubMed:27313224). Also serves as a receptor for the closely related C.botulinum neurotoxin type A2; glycosylation is not essential but enhances the interaction (PubMed:29649119). (Microbial infection) Possible receptor for C.botulinum neurotoxin type D (BoNT/D, botD); note that type D does not usually infect humans. Interacts with SYT1 in a calcium-dependent manner. (Microbial infection) Interacts with C.botulinum neurotoxin type A1 and type A2 (BoNT/A, botA) (PubMed:29649119). Interaction is improved by glycosylation of SV2 (PubMed:29649119). Enriched in small synaptic vesicles and adrenal microsomes, not present in chromaffin granules. Associated with both insulin granules and synaptic-like microvesicles in insulin-secreting cells of the pancreas. N-glycosylated. Upon expression in a kidney cell line the most abundant glycan on Asn-534 is GlcNAc(3)Hex(5), while on Asn-559 and Asn-565 the most abundant glycan is GlcNAc2Fuc1Man3GlcNAc3Gal3. Both Asn-559 and Asn-565 have a high degree of glycan heterogeneity (PubMed:27313224). Belongs to the major facilitator superfamily.