ADP-rlbosylation of regulatory proteins is an important mechanism by which bacterial toxins affect the eukaryotic organism.9,27,32 Diphtheria toxin and Pseudomonas aeruginosa exotoxin A modify elongation factor 2 thereby inhibiting protein synthesis.9,26,32 Cholera toxin, Escherichia coli heat-labile enterotoxin and pertussis toxin ADP-ribosylate regulatory G-proteins involved in a variety of transmembranous signaling processes in eukaryotic cells.8,9,28,32 These G-proteins (Gg, Gi, Go, transducin) comprise a family of highly homologous proteins of heterotrimeric structure,25 which function by utilizing a guanine nucleotide binding and GTPase cycle. The toxins ADP-ribosylate the α-subunit of the G-proteins thereby either enhancing (cholera toxin) or inhibiting (pertussis toxin) signal transduction.25
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Aktories et al. (1989) studied this question.