Structural Basis for the Function of Clostridium difficile Toxin B

• Published in: Journal of molecular biology Vol. 351; no. 5; pp. 973 - 981
• Main Authors: Reinert, Dirk J., Jank, Thomas, Aktories, Klaus, Schulz, Georg E.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 02.09.2005
• Subjects: Bacterial Proteins - genetics; Bacterial Toxins - genetics; Binding Sites; Carbon - chemistry; Catalysis; clostridial cytotoxins; Clostridium difficile; Clostridium difficile - metabolism; Crystallography, X-Ray; Escherichia coli - metabolism; Glucose - chemistry; glucosyltransfer reaction; Glutathione Transferase - metabolism; glycosyltransferases; Glycosyltransferases - metabolism; Hydrolysis; Ligands; Manganese - chemistry; Models, Molecular; Molecular Conformation; Mutation; Protein Binding; Protein Conformation; Protein Isoforms; Rho proteins; Stereoisomerism; Uridine Diphosphate - chemistry; Uridine Diphosphate Glucose - chemistry; X-ray structure analysis; clostridial cytotoxins; glycosyltransferases; MAD; Gal; cisPt; GlcNAc; SIRAS; X-ray structure analysis; Rho proteins; glucosyltransfer reaction; Glc
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2005.06.071

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 Mn 2+. The structure was determined at 2.2 Å 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 γ1 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.