Structure-function relationships in Escherichia coli translational elongation factor G: modification of lysine residues by the site-specific reagent pyridoxal phosphate

Translational elongation factor G (EF-G) of Escherichia coli was modified with the selective, site-specific lysine reagent pyridoxal phosphate (PLP). The reaction results in the modification of a maximum of 12 lysine residues, one of which is essential for guanosine 5'-triphosphate (GTP) binding and whose modification is inhibited by the presence of GTP. Formation of a reversible adduct between 2,3-butanedione and an essential arginine similarly located in the GTP binding site [Rohrbach, M.S., & Bodley, J. W. (1977) Biochemistry 16, 1360-1363] also protects EF-G from PLP inactivation, suggesting that these two residues are spatially close to each other in the native factor. The essential lysine residue was found in the trypsin-resistant fragment T4 (Mr 41 000). In addition to the lysine essential for GTP binding, at least one further lysine was found to be important for EF-G function, since GTP-protected, PLP-modified EF-G molecules fully competent in binding to 50S ribosomal subunits showed decreased activity in 50S- and 70S-dependent GTP hydrolysis. It is likely that a PLP-modified lysine impairs the interaction of the factor with 30S ribosomal subunits and/or a conformational change of the factor required for the hydrolysis of GTP.