Cholera toxin (CT) is a heat-sensitive multimeric protein enterotoxin produced by Vibrio cholera*, which transfers ADP-ribose to a G protein, locking adenyl cyclase in an “on” position by ADP ribosylation of a Gs protein.
*Composed of five 11.6 kD cell-binding B subunits forming a ring around a finger-like subunit A, a 27 kD catalase. CT’s functional properties are shared by Bordetella pertussis toxin, diphtheria toxin, and exotoxin A.
Mechanism The B subunit ring of CT binds to GM1 gangliosides on the surface of target cells. Once bound, the entire toxin complex is endocytosed by the cell, releasing the cholera toxin A1 (CTA1) chain by a disulfide bridge reduction. The endosome moves to the Golgi apparatus, where the A1 protein is recognised by the endoplasmic reticulum chaperone, protein disulfide isomerase.