Properties of elongation factor-2 fragments obtained by partial proteolysis

Rat liver elongation factor eEF-2 was treated with endoproteinase Glu-C. Two major fragments were obtained, which were identified by N-terminal sequencing and purified. The larger one (F61) contained 554 residues including the N-terminal end, and after a second cleavage released a N-terminal peptide (F7) of 62 residues. The smaller one (F34) contained the other 303 residues including the C terminal end. F61 and F34, either isolated or after combination, were unable to catalyze protein synthesis. However, we show by fluorimetry that F61 could still interact with GTP and GDP. This fragment was was able to participate into a ternary complex with ribosome and GDP, but not with ribosome and a GTP analogue. It was unable to protect the ribosome against ricin-inactivation and to be phosphorylated by the eEF-2-specific Ca(2+)-calmodulin-dependent kinase, though it contained Trp221 and Thr56 involved in these reactions. On the other hand, F34 could be ADP-ribosylated in the presence of NAD+ and diphtheria toxin, but this fragment was apparently unable to bind to ribosomes. These results and those obtained with other proteinases are discussed in the light of the data published recently which show the existence of five different domains in the three-dimensional structure of EF-G.