title: Structural basis for the function of Clostridium difficile toxin B.
abstract: Toxin B is a member of the family of large clostridial cytotoxins which are of great medical importance. Its catalytic fragment was crystallized in the presence of UDP-glucose and Mn2+. The structure was determined at 2.2 A resolution, showing that toxin B belongs to the glycosyltransferase type A family. However, toxin B contains as many as 309 residues in addition to the common chainfold, which most likely contribute to the target specificity. A superposition with other glycosyltransferases shows the expected positions of the acceptor oxygen atom during glucosyl transfer and indicates further that the reaction proceeds probably along a single-displacement pathway. The C1'' donor carbon atom position is defined by the bound UDP and glucose. It assigns the surface area of toxin B that forms the interface to the target protein during the modifying reaction. A docking attempt brought the known acceptor atom, Thr37 O(gamma1) of the switch I region of the RhoA:GDP target structure, near the expected position. The relative orientation of the two proteins was consistent with both being attached to a membrane. Sequence comparisons between toxin B variants revealed that the highest exchange rate occurs around the active center at the putative docking interface, presumably due to a continuous hit-and-evasion struggle between Clostridia and their eukaryotic hosts.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, 79104 Freiburg im Breisgau, Germany.
authors.forename: Dirk J
authors.initials: DJ
authors.lastname: Reinert
authors.forename: Thomas
authors.initials: T
authors.lastname: Jank
authors.forename: Klaus
authors.initials: K
authors.lastname: Aktories
authors.forename: Georg E
authors.initials: GE
authors.lastname: Schulz
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001427:Bacterial Toxins / Q000235:genetics*; D001665:Binding Sites; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D016360:Clostridioides difficile / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism; D005947:Glucose / Q000737:chemistry; D005982:Glutathione Transferase / Q000378:metabolism; D016695:Glycosyltransferases / Q000378:metabolism; D006868:Hydrolysis; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms; D013237:Stereoisomerism; D014530:Uridine Diphosphate / Q000737:chemistry; D014532:Uridine Diphosphate Glucose / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D008024:Ligands; D020033:Protein Isoforms; C031815:toxB protein, Clostridium difficile; D008345:Manganese; D014530:Uridine Diphosphate; D002244:Carbon; D016695:Glycosyltransferases; D005982:Glutathione Transferase; D005947:Glucose; D014532:Uridine Diphosphate Glucose