The effect of Mg2+ on some properties of nucleotide-free elongation factor Tu from Bacillus stearothermophilus.

The nucleotide-free elongation factor from Bacillus stearothermophilus provides a means to study the effect of Mg2+ ions on various reactions of the protein. The binding of GDP to the protein is stimulated by Mg2+. From comparative studies with other metal ions, particularly Mn2+, it appears that this stimulation is due to the formation of a metal - GDP complex which is bound to the protein. Protection against proteolysis by trypsin is afforded by both Mg2+ and Mg - GDP, but not by GDP alone. The rate of substitution of the sulphydryl group associated with aminoacyl-tRNA binding, either 5,5'-dithio-bis(2-nitrobenzoic acid) or N-ethylmaleimide is reduced in the presence of Mg2+ - All these observations show that Mg2+ not only is involved in GDP binding but also has a direct effect on the tertiary structure of the protein.