Clostridium difficile is a common nosocomial pathogen and a major cause of infectious diarrhea in hospitalized patients. Two structurally similar toxins denoted as TcdA and TcdB are the main virulence determinants associated with Clostridium difficile-associated disease. The TcdB is encoded by the tcdB gene and is pro-inflammatory, cytotoxic, and enterotoxic in the human colon. The molecular weight of TcdB is 270 kDa. TcdB is a glucosyltransferase that catalyzes the monoglucosylation of threonine 35/37 of small GTP-binding proteins Rho, Rac, and Cdc42 within target cells, and thus modulates several physiological cellular events resulting in cell death. Structurally TcdB contains three domains: the enzymatic activity is located in the N terminus of the protein, the middle domain is the putative translocation region, and the C terminus is involved in receptor binding. The N termini of TcdA and TcdB demonstrate 74% homology that accounts for their similar substrate specificity. The carboxy-terminal domain of both toxins carries a number of short homologous regions termed combined repetitive oligopeptides (CROPs).
A number of studies have demonstrated that the presence of TcdB in mammalian cells leads to rapid changes in cell morphology and cell signaling. Within a short period of time, cells have the appearance of plaque, even with small dosages of TcdB and TcdA.
For Research Use Only. NOT FOR CLINICAL USE.
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