Carbohydrate recognition by Clostridium difficile toxin A

Clostridium difficile TcdA is a large toxin that binds carbohydrates on intestinal epithelial cells. A 2-angstrom resolution cocrystal structure reveals two molecules of alpha-Gal-(1,3)-beta-Gal-(1,4)-beta-GlcNAcO(CH2)(8)CO2CH3 binding in an extended conformation to TcdA. Residues forming key contacts with the trisaccharides are conserved in all seven putative binding sites in TcdA, suggesting a mode of multivalent binding that may be exploited for the rational design of novel therapeutics.