Functional properties of the carboxy-terminal host cell-binding domains of the two toxins, TcdA and TcdB, expressed by Clostridium difficile

Glycobiology. 2008 Sep;18(9):698-706. doi: 10.1093/glycob/cwn048. Epub 2008 May 28.


The biological and ligand-binding properties of recombinant C-terminal cell-binding domains (CBDs) and subdomains of the two large exotoxins, Toxin A (TcdA) and Toxin B (TcdB) expressed by Clostridium difficile were examined in the hemagglutination and Verocytotoxicity neutralization assays and by qualitative affinity chromatography using Sepharose-linked alpha Gal(1,3)betaGal(1,4)beta Glc as well as the direct electrospray ionization mass spectrometry (ES-MS) assay. These studies revealed that, whereas the full-length TcdA CBD agglutinated rabbit erythrocytes, neutralized TcdA-mediated Vero cell death and bound to alpha Gal(1,3)betaGal(1,4)beta Glc-derivatized Sepharose, the TcdB CBD was inactive in these functional assays. Moreover, retention by alpha Gal(1,3)betaGal(1,4)beta Glc-derivatized Sepharose corresponded to the number of available TcdA subdomain ligand-binding sites. By contrast, the ES-MS assays revealed that both the TcdA and TcdB CBD bind to 8-methoxycarbonyloctyl-alpha Gal(1,3)betaGal(1,4)beta Glc sequences with similar avidities. Additional ES-MS experiments using chemically altered alpha Gal(1,3)betaGal(1,4)beta Glc sequences also revealed that the TcdA and TcdB CBD will tolerate a fair amount of structural variation in their complementary glycan ligands. Although the studies are consistent with the known ligand-binding properties of the TcdA and TcdB holotoxins, they also revealed subtle heretofore unrecognized functional differences in their receptor recognition properties.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Bacterial Proteins / physiology*
  • Bacterial Toxins / chemistry*
  • Bacterial Toxins / metabolism
  • Chlorocebus aethiops
  • Clostridioides difficile / metabolism
  • Enterotoxins / chemistry*
  • Enterotoxins / metabolism
  • Enterotoxins / physiology*
  • Host-Pathogen Interactions / physiology
  • Models, Biological
  • Models, Molecular
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Peptide Fragments / physiology
  • Protein Binding
  • Protein Structure, Tertiary / physiology
  • Toxicity Tests
  • Vero Cells


  • Bacterial Proteins
  • Bacterial Toxins
  • Enterotoxins
  • Peptide Fragments
  • tcdA protein, Clostridium difficile
  • toxB protein, Clostridium difficile