Carbohydrate recognition by Clostridium difficile toxin A

Abstract

Clostridium difficile TcdA is a large toxin that binds carbohydrates on intestinal epithelial cells. A 2-A resolution cocrystal structure reveals two molecules of alpha-Gal-(1,3)-beta-Gal-(1,4)-beta-GlcNAcO(CH(2))(8)CO(2)CH(3) 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.

Structural organization of the functional domains of Clostridium difficile toxins A and B

“…1A). The toxins first bind the surface of the target cell through a highly repetitive C-terminal domain (6,7) and are internalized by endocytosis (8,9). The low pH of the endosome is proposed to induce structural changes that lead to pore formation and translocation of the N terminus across the membrane (9)(10)(11).…”

“…We have determined a 3D structure of the TcdA holotoxin at neutral pH by negative stain EM and experimentally mapped three of the four functional domains to discrete regions within the density. These data allow us to evaluate structural models of the TcdA receptor-binding domain (6,18), the TcdA autoprotease domain (19), and the TcdB glucosyltransferase domain (20) within the architecture of the holotoxin. In addition to the analysis at neutral pH, we present images of TcdA after autoprocessing and after exposure to acidic pH.…”

Role of the C-terminal region of dextransucrase from Leuconostoc mesenteroides IBT-PQ in cell anchoring

“…A DsrP C-terminal domain model was constructed based on the known structures of the CWBR of LytA and ToxA (GenBank accession nos 1GVMB and 2F6EA) (Fernández-Tornero et al, 2001, 2002Ho et al, 2005;Greco et al, 2006). Both the Geno3D and the SWISS-MODEL programs retrieved equivalent structural models from C-terminal domain sequences.…”

“…This region also adopts a b-solenoid fold. Residues that interact with the carbohydrate are conserved in all seven putative binding sites in TcdA, suggesting a multivalent binding mode (Greco et al, 2006). Several streptococcal GSs and Leuconostoc dextransucrases are present in both the pellet and the supernatant fractions of cultures when strains are grown in the presence of sucrose; it is usually assumed that insoluble GSs are the result of binding to high-molecular-weight dextran that pellets together the enzyme and the cells.…”

Self-Cutting To Kill: New Insights into the Processing ofClostridium difficileToxins

“…Analysis of the crystal structure of a C-terminal fragment of 127 residues of toxin A revealed a ␤-solenoid fold with 32 short repeats of 15-21 residues and 7 long repeats consisting of 30 residues, with each repeat consisting of a ␤-hairpin followed by a loop (9). Moreover, cocrystallization of the polypeptide repeats with a synthetic carbohydrate structure derived from a putative receptor carbohydrate allowed the first insights into the interaction of the toxins with carbohydrate receptor structures (10). Recently, the crystal structure of the N-terminal enzyme domain, which is transported into the cytosol, was solved.…”