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 binds via extracellular loop 4 (PubMed:16543415). Restores uptake of BoNT/A in mouse cells that are deleted for SV2 receptor (PubMed:16543415, PubMed:18815274). Glycosylation of Asn-573 is not essential for receptor activity, but enhances uptake (PubMed:18815274, PubMed:19650874). Also serves as a receptor for the closely related C.botulinum neurotoxin type A2; glycosylation is not essential but enhances the interaction (PubMed:29649119). Possible receptor for C.botulinum neurotoxin type D (BoNT/D, botD); BoNT/D does not bind to extracellular loop 4 as do BoNT/A and BoNT/E, nor to loop 1 or loop 3 (PubMed:21483489). Another group does not find a convincing interaction with SV2 (PubMed:21632541). (Microbial infection) Receptor for C.botulinum neurotoxin type E (BoNT/E); the toxin probably binds via extracellular loop 4 and requires glycosylation of Asn-573 (PubMed:18815274, PubMed:19650874). Restores uptake of BoNT/E in mouse cells that are deleted for SV2 receptor (PubMed:18815274). (Microbial infection) Receptor for C.botulinum neurotoxin type F (BoNT/F) (PubMed:19476346, PubMed:19650874). Binding requires glycosylation of Asn-573 (PubMed:19476346). Interacts with SYT1/synaptotagmin-1 in a calcium-dependent manner. Binds the adapter protein complex AP-2. (Microbial infection) Interacts with C.botulinum neurotoxin type A1 and type A2 (BoNT/A, botA) (PubMed:16543415, PubMed:19650874, PubMed:21632541, PubMed:21483489, PubMed:29649119). Interaction is improved by glycosylation of SV2 (PubMed:29649119). (Microbial infection) Copurifies with C.botulinum neurotoxin type B (BoNT/B, botB) and synaptotagmin 1 (SYT1) (PubMed:19476346). Interaction does not require glycosylation of SV2 or SYT1 proteins (PubMed:19476346). Another group finds only copurification with SYT1 and SYT2 (PubMed:19650874). (Microbial infection) Interacts with C.botulinum neurotoxin type E (BoNT/E) (PubMed:18815274, PubMed:19476346, PubMed:19650874). Interaction requires glycosylation of SV2 proteins (PubMed:18815274, PubMed:19476346, PubMed:19650874). (Microbial infection) Copurifies with C.botulinum neurotoxin type F (BoNT/F) and synaptotagmin 1 (SYT2) (PubMed:19476346). Another group finds only copurification with BoNT/F (PubMed:19650874). Interaction requires SV2 glycosylation (PubMed:19476346). Enriched in chromaffin granules, not present in adrenal microsomes. Associated with both insulin granules and synaptic-like microvesicles in insulin-secreting cells of the pancreas. Colocalizes with ATP2B1 at photoreceptor synaptic terminals. Widely expressed throughout the brain (at protein level). Expressed by neural and endocrine cells of brain and spinal cord. Phosphorylation by CK1 of the N-terminal cytoplasmic domain regulates interaction with SYT1. N-glycosylated, on at least 3 residues. Short hairpin-mediated RNA knockdown of the protein in PC12 cells leads to increased resistance to C.botulinum neurotoxin type A (BoNT/A, botA) as assayed by reduced SNAP25 cleavage; uptake and degradation are restored by expression of SV2B or SV2C (PubMed:16543415). Identified as the brain binding-site for the antiepileptic drug levetiracetam/lev. Belongs to the major facilitator superfamily. The use of this protein as a coreceptor for C.botulinum type D (BoNT/D, botD) is controversial. In double SV2A/SV2B knockout mice BoNT/D does not degrade its synaptobrevin target; introducing SV2A, SV2B or SV2C restores target cleavage (PubMed:21483489). However another group does not find a convincing interaction with SV2 (PubMed:21632541).