Clostridioides difficile toxin A (TcdA) and Sucrase-isomaltase (SI) receptor (TcdA-SI)

Clostridioides difficile toxin A (TcdA) is a high-molecular-weight enterotoxin and a primary virulence factor produced by the Gram-positive bacterium C. difficile (UniProt P15928). It exerts its pathogenic effects by binding to specific receptors on the intestinal brush border, most notably the enzyme sucrase-isomaltase (SI) in humans (UniProt P14410; Pothoulakis et al., 1996). Upon binding, TcdA is internalized via receptor-mediated endocytosis, followed by the translocation of its N-terminal glucosyltransferase domain into the host cell cytosol. Once inside, TcdA catalyzes the irreversible glucosylation of Rho family GTPases, such as Rho, Rac, and Cdc42, which are essential for maintaining the actin cytoskeleton and epithelial barrier integrity (Gerhard et al., 2015). This molecular disruption leads to cell rounding, loss of tight junctions, and a robust inflammatory response, resulting in the clinical symptoms of C. difficile infection (CDI), including severe diarrhea and pseudomembranous colitis. Therapeutic agents like the monoclonal antibody actoxumab (MK-3415) have been developed to neutralize TcdA by binding to its C-terminal repetitive domains, thereby preventing its interaction with intestinal receptors and subsequent cellular entry (Wilcox et al., 2017).

Other names

Toxin AEnterotoxin ATcdASucrase-isomaltaseSIClostridium difficile Toxin AC. difficile Toxin A receptor

Neutralizing monoclonal antibodies bind to the C-terminal combined repetitive oligopeptides (CROP) domain of TcdA, preventing the toxin from attaching to its intestinal brush border receptors, such as sucrase-isomaltase, thereby inhibiting toxin internalization and subsequent cytopathic effects.