The complete receptor-binding domain of Clostridium difficile toxin A is required for endocytosis

Biochem Biophys Res Commun. 2003 Jan 17;300(3):706-11. doi: 10.1016/s0006-291x(02)02919-4.


Clostridium difficile toxin A, the chief pathogenicity factor of the antibiotic-associated pseudomembranous colitis, is an intracellular acting cytotoxin that reaches its targets, the Rho GTPases, after receptor-mediated endocytosis. The C-terminal part, constructed of repetitive peptide elements, is thought to bind to a lot of carbohydrate containing receptor molecules to induce clustering and endocytosis. To study which part of the receptor-binding domain is in charge of addressing toxin A into the target cells, we studied the functional, i.e., endocytosis-inducing, binding of toxin A. By a competition assay between various receptor-binding fragments of toxin A and the holotoxin A we found that the complete receptor-binding domain, encompassing the entire repetitive elements, but not parts of it, is necessary for binding-induced endocytosis. The receptor binding domain itself shows weaker competition with holotoxin A than the fragment consisting of receptor-binding domain plus intermediary part of the toxin. All toxin A fragments that compete with holotoxin A are capable of inducing their own endocytosis. Thus, the entire receptor-binding domain, covering the C-terminal third of the toxin A molecule, is responsible for cell uptake of toxin A and the intermediary part contributes to the correct folding and assembly of the repetitive domains.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Toxins / chemistry*
  • Bacterial Toxins / metabolism
  • Bacterial Toxins / toxicity
  • Binding, Competitive / physiology
  • Cell Count
  • Cell Survival / drug effects
  • Endocytosis / drug effects
  • Endocytosis / physiology*
  • Enterotoxins / chemistry*
  • Enterotoxins / metabolism
  • Enterotoxins / toxicity
  • HT29 Cells
  • Humans
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Peptide Fragments / toxicity
  • Protein Binding / physiology
  • Protein Structure, Tertiary / physiology
  • Receptors, Cell Surface / metabolism*
  • Temperature


  • Bacterial Toxins
  • Enterotoxins
  • Peptide Fragments
  • Receptors, Cell Surface
  • tcdA protein, Clostridium difficile