title: Botulinum neurotoxin B recognizes its protein receptor with high affinity and specificity.
abstract: Botulinum neurotoxins (BoNTs) are produced by Clostridium botulinum and cause the neuroparalytic syndrome of botulism. With a lethal dose of 1 ng kg(-1), they pose a biological hazard to humans and a serious potential bioweapon threat. BoNTs bind with high specificity at neuromuscular junctions and they impair exocytosis of synaptic vesicles containing acetylcholine through specific proteolysis of SNAREs (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors), which constitute part of the synaptic vesicle fusion machinery. The molecular details of the toxin-cell recognition have been elusive. Here we report the structure of a BoNT in complex with its protein receptor: the receptor-binding domain of botulinum neurotoxin serotype B (BoNT/B) bound to the luminal domain of synaptotagmin II, determined at 2.15 A resolution. On binding, a helix is induced in the luminal domain which binds to a saddle-shaped crevice on a distal tip of BoNT/B. This crevice is adjacent to the non-overlapping ganglioside-binding site of BoNT/B. Synaptotagmin II interacts with BoNT/B with nanomolar affinity, at both neutral and acidic endosomal pH. Biochemical and neuronal ex vivo studies of structure-based mutations indicate high specificity and affinity of the interaction, and high selectivity of BoNT/B among synaptotagmin I and II isoforms. Synergistic binding of both synaptotagmin and ganglioside imposes geometric restrictions on the initiation of BoNT/B translocation after endocytosis. Our results provide the basis for the rational development of preventive vaccines or inhibitors against these neurotoxins.
authors.affiliation: Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA.
authors.forename: Rongsheng
authors.initials: R
authors.lastname: Jin
authors.forename: Andreas
authors.initials: A
authors.lastname: Rummel
authors.forename: Thomas
authors.initials: T
authors.lastname: Binz
authors.forename: Axel T
authors.initials: AT
authors.lastname: Brunger
mesh_terms: D000818:Animals; D001665:Binding Sites; D001905:Botulinum Toxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019274:Botulinum Toxins, Type A; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D013379:Substrate Specificity; D050863:Synaptotagmin I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050861:Synaptotagmin II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D050863:Synaptotagmin I; D050861:Synaptotagmin II; C096323:rimabotulinumtoxinB; D001905:Botulinum Toxins; D019274:Botulinum Toxins, Type A