ABSTRACT
The principal pathological effects produced by several bacterial species are mediated by a class of secreted enzyme toxins, termed ADP-ribosyltransferases. The enzymatic toxins of Bordetella pertussis, Vibrio choierae, and enterotoxigenic Escherichia coli exert their action by covalent modification of the a-subunit of heterotrimeric guanyl nucleotide-binding proteins (G proteins) involved in the transduction of certain receptor-coupled agonist regulatory signals that modulate control of intracellular adenylate cyclase. Cholera toxin and the heat-labile enterotoxins of E. coli are, respectively, the direct cause of the diarrhea and vomiting resulting from infection with V. choierae and enterotoxigenic E. coli. Cholera toxin and the LTs share a common oligomeric structure, consisting of an A protomer and B oligomer. Each of these three ADP-ribosylating toxins conform to an A-B structural organization: an active (A) subunit possessing catalytic potential and a binding (B) subunit involved in cellular recognition.
