ADP ribosylation of elongation factor (EF)-2 by DT or ExoA blocks interaction of GTP-bound EF-2 with the ribosome in the pretranslocation phase of the peptideelongation cycle, which prevents formation of the high-affinity complex and stimulation of the GAP activity of EF-2 by the ribosome. ADP ribosylation of EF-2 does not interfere with GTP or GDP binding to EF-2, but may inhibit the exchange of GDP with GTP.
DT: Diphtheria toxin; GAP: GTPase activating protein; GEF: Guanine nucleotide exchange factor.