Structural basis for the function of Clostridium difficile toxin B

J Mol Biol. 2005 Sep 2;351(5):973-81. 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 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Toxins / genetics*
  • Binding Sites
  • Carbon / chemistry
  • Catalysis
  • Clostridioides difficile / metabolism
  • Crystallography, X-Ray
  • Escherichia coli / metabolism
  • Glucose / chemistry
  • Glutathione Transferase / metabolism
  • Glycosyltransferases / metabolism
  • Hydrolysis
  • Ligands
  • Manganese / chemistry*
  • Models, Molecular
  • Molecular Conformation
  • Mutation
  • Protein Binding
  • Protein Conformation
  • Protein Isoforms
  • Stereoisomerism
  • Uridine Diphosphate / chemistry
  • Uridine Diphosphate Glucose / chemistry*


  • Bacterial Proteins
  • Bacterial Toxins
  • Ligands
  • Protein Isoforms
  • toxB protein, Clostridium difficile
  • Manganese
  • Uridine Diphosphate
  • Carbon
  • Glycosyltransferases
  • Glutathione Transferase
  • Glucose
  • Uridine Diphosphate Glucose

Associated data

  • PDB/2BVL
  • PDB/2BVM