Pertussis toxin

Pertussis toxin (PT) is a protein-based AB5-type exotoxin produced by the bacterium Bordetella pertussis. PT is involved in the colonization of the respiratory tract and the establishment of infection. Research suggests PT may have a therapeutic role in treating a number of common human ailments including hypertension, viral inhibition, and autoimmune inhibition.

Mechanism of pathogenesis
PT is an exotoxin with six subunits (named S1 through S5&mdash;each complex contains two copies of S4). The subunits are arranged in a A-B structure: the A component is enzymatically active and is formed from the S1 subunit, while the B component is the receptor-binding portion and is made up of subunits S2–S5. The subunits are encoded by ptx genes encoded on a large PT operon that also includes additional genes which encode Ptl proteins: Together these proteins form the PT secretion complex.

PT is released from B. pertussis in an inactive form. When the B subunit binds to a cell membrane receptor, the A subunit (or protomer) becomes activated, perhaps through the action of glutathione and ATP. PT catalyzes the ADP-ribosylation of the α subunits of the heterotrimeric guanine nucleotide regulatory proteins Gi, Go, and Gt. This prevents the G-proteins from interacting with cell membrane receptors, thus interfering with intracellular communication. Since the Gα subunits remain in their GDP-bound, inactive state, they are unable to inactivate adenylyl cyclase or open potassium channels.