title: Crystal structure of the botulinum neurotoxin type G binding domain: insight into cell surface binding.
abstract: Botulinum neurotoxins (BoNTs) typically bind the neuronal cell surface via dual interactions with both protein receptors and gangliosides. We present here the 1.9-A X-ray structure of the BoNT serotype G (BoNT/G) receptor binding domain (residues 868-1297) and a detailed view of protein receptor and ganglioside binding regions. The ganglioside binding motif (SxWY) has a conserved structure compared to the corresponding regions in BoNT serotype A and BoNT serotype B (BoNT/B), but several features of interactions with the hydrophilic face of the ganglioside are absent at the opposite side of the motif in the BoNT/G ganglioside binding cleft. This may significantly reduce the affinity between BoNT/G and gangliosides. BoNT/G and BoNT/B share the protein receptor synaptotagmin (Syt) I/II. The Syt binding site has a conserved hydrophobic plateau located centrally in the proposed protein receptor binding interface (Tyr1189, Phe1202, Ala1204, Pro1205, and Phe1212). Interestingly, only 5 of 14 residues that are important for binding between Syt-II and BoNT/B are conserved in BoNT/G, suggesting that the means by which BoNT/G and BoNT/B bind Syt diverges more than previously appreciated. Indeed, substitution of Syt-II Phe47 and Phe55 with alanine residues had little effect on the binding of BoNT/G, but strongly reduced the binding of BoNT/B. Furthermore, an extended solvent-exposed hydrophobic loop, located between the Syt binding site and the ganglioside binding cleft, may serve as a third membrane association and binding element to contribute to high-affinity binding to the neuronal membrane. While BoNT/G and BoNT/B are homologous to each other and both utilize Syt-I/Syt-II as their protein receptor, the precise means by which these two toxin serotypes bind to Syt appears surprisingly divergent.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Pål
authors.initials: P
authors.lastname: Stenmark
authors.forename: Min
authors.initials: M
authors.lastname: Dong
authors.forename: Jérôme
authors.initials: J
authors.lastname: Dupuy
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Chapman
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Stevens
mesh_terms: D000818:Animals; D001665:Binding Sites; D001905:Botulinum Toxins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D005732:Gangliosides / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism; D050857:Synaptotagmins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005732:Gangliosides; D011956:Receptors, Cell Surface; D050857:Synaptotagmins; C488535:botulinum toxin type G; D001905:Botulinum Toxins