1-N6-Etheno-ADP-ribosylation of elongation factor-2 by diphtheria toxin

Diphtheria toxin fragment A is able to inhibit protein synthesis in the eukaryotic cell by ADP-ribosylating the diphthamide residue of elongation factor-2 (EF-2) [(1980) J. Biol. Chem. 255, 10710-10720]. The reaction requires NAD as ADP-ribose donor. This work reports on the capacity of an NAD analog, the nicotinamide 1-N6-ethenoadenine dinucleotide (epsilon NAD), to be a substrate of diphtheria toxin fragment A in the transferring reaction of the fluorescent moiety, the epsilon ADP-ribose, to the EF-2. As a consequence of the transfer of the epsilon ADP-ribosyl moiety to the EF-2, there is an increase in the emission intensity of the fluorophore and a blue shift in its emission maximum. The epsilon ADP-ribosylated EF-2, like ADP-ribosylated EF-2, retains the capacity to bind GTP and ribosome. The utility of introducing a fluorescent probe in a well defined point of the EF-2 molecule for conformational or binding studies is discussed.