Cholera toxin, the pathogenic agent of cholera, is made of two subunits, A (27 kDa) and B (12 kDa) assembled with the stoichiometry AB5. The B-subunit binds to specific receptors, the monosialogangliosides GM1, located in the membrane of intestinal epithelial cells. The A1 fragment of the A-subunit is translocated through the membrane of the host cell, where it catalyses the ADP-ribosylation of the Gsa regulatory component of the adenylate cyclase complex. The resulting increased level of cyclic AMP promotes a wide variety of actions, including the secretion of chloride ions in the case of intestinal epithelial cells.
Cholera toxin (CT), a multifunctional protein plays a role in the immune system. It possesses immunomodulatory, adjuvant properties and also acts as an anti-inflammatory agent. Its immunomodulatory properties can be utilized to treat several autoimmune disorders. CT can serve as one of the best model of a multifunctional protein.
