Mono-ADP-ribosylating toxins catalyze the transfer of ADP_ribose from NAD+ to eukaryotic Elongation Factor 2, halting protein synthesis. A single molecule of delivered toxin is sufficient to kill a cell. These toxins share mono-ADP-ribosylating activity with a variety of bacterial toxins, such as cholera toxin and pertussis toxin. The structural core is homologous to the poly-ADP ribosylating enzymes such as the PARP enzymes and Tankyrase. Diphtheria toxin is encoded by a lysogenic bacteriophage. Both diphtheria toxin and Pseudomonas aeruginosa exotoxin A are multi-domain proteins. These domains provide a EF2 ADP_ribosylating, receptor-binding, and intracellular trafficking/transmembrane functions .
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