Discussion
Which one of the following bacterial toxins does NOT have ADP-ribosyl transferase activity?
Answer: D
The toxin without ADP-ribosyl transferase activity is S. aureus α-toxin.
α-toxin (α-haemolysin) of Staphylococcus aureus is a pore-forming toxin: its monomers assemble into a heptameric beta-barrel pore in the target cell membrane, letting ions leak and lysing the cell. It has no enzymatic activity.
The other three are ADP-ribosylating toxins. Diphtheria toxin and Pseudomonas exotoxin A both ADP-ribosylate elongation factor 2 and halt protein synthesis, and pertussis toxin ADP-ribosylates the inhibitory G protein Gi, uncoupling it from its receptors.
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