Effect of ADP-ribosylation and phosphorylation on the interaction of elongation factor 2 with guanylic nucleotides.

Samples of unmodified EF-2, EF-2 ADP-ribosylated with diphtheria toxin and NAD, and/or phosphorylated using ATP and the Ca(2+)-calmodulin dependent kinase III partially purified, were irradiated at 254 nm with 32P-labeled GDP or GTP, and analyzed by one- and two-dimensional gel electrophoresis. By this method we showed that unmodified EF-2 formed a stable complex with GDP but not with GTP, whereas phosphorylated EF-2 and ADP-ribosylated + phosphorylated EF-2 formed stable complexes even in the absence of irradiation, with GTP but not GDP. ADP-ribosylated EF-2 did not form stable complexes with either GDP or GTP. Prior ADP-ribosylation of EF-2 increased its ability to the phosphorylated. These results show that the structures of the two domains containing diphtamide 715 and the phosphorylatable threonines (between Ala 51 and Arg 60) are interdependent; modifications of these residues induce different conformational changes of EF-2 which alter the interactions of the factor with guanylic nucleotides as well with ribosomes.