Structural basis for recognition of synaptic vesicle protein 2C by botulinum neurotoxin A.

Botulinum neurotoxin A (BoNT/A) belongs to the most dangerous class of bioweapons(1). Despite this, BoNT/A is used to treat a wide range of common medical conditions such as migraines and a variety of ocular motility and movement disorders(2). BoNT/A is probably best known for its use as an antiwrinkle agent in cosmetic applications (including Botox and Dysport)(3). BoNT/A application causes long-lasting flaccid paralysis of muscles through inhibiting the release of the neurotransmitter acetylcholine by cleaving synaptosomal-associated protein 25 (SNAP-25) within presynaptic nerve terminals(4). Two types of BoNT/A receptor have been identified, both of which are required for BoNT/A toxicity and are therefore likely to cooperate with each other(5): gangliosides and members of the synaptic vesicle glycoprotein 2 (SV2) family, which are putative transporter proteins that are predicted to have 12 transmembrane domains, associate with the receptor-binding domain of the toxin(5). Recently, fibroblast growth factor receptor 3 (FGFR3) has also been reported to be a potential BoNT/A receptor(6). In SV2 proteins, the BoNT/A-binding site has been mapped to the luminal domain(7), but the molecular details of the interaction between BoNT/A and SV2 are unknown. Here we determined the high-resolution crystal structure of the BoNT/A receptor-binding domain (BoNT/A-RBD) in complex with the SV2C luminal domain (SV2C-LD). SV2C-LD consists of a right-handed, quadrilateral beta-helix that associates with BoNT/A-RBD mainly through backbone-to-backbone interactions at open beta-strand edges, in a manner that resembles the inter-strand interactions in amyloid structures. Competition experiments identified a peptide that inhibits the formation of the complex. Our findings provide a strong platform for the development of novel antitoxin agents and for the rational design of BoNT/A variants with improved therapeutic properties.