Cholera Toxin (CT): Secretion by the Vibrios

The secretion of cholera toxin (CT) by the organism Vibrio cholerae involves different sets of proteins spanning the inner and outer membrane of the bacterial cell. In the bacterial cytosol, the subunits A and B are synthesized as unfolded chains with N-terminal signal peptide. These unfolded chains are then translocated across the inner membrane via the Sec-dependent pathway to reach the periplasmic space. Here, the chains are freed of the signal peptides; they then fold to achieve their respective 3D structures and ultimately assemble into the AB₅ type of holotoxin structure. This fully formed CT holotoxin is then translocated across the outer membrane via another secretory pathway spanning the inner and outer membranes, which is known as the type II secretion system (T2SS) or the Eps (extra cellular protein secretion) system of V. cholerae. Both of these secretion channels consist of multiprotein complexes, whose organizations and functions govern the secretion of CT by V. cholerae.