Effect of Thermus thermophilus elongation factor Ts on the conformation of elongation factor Tu

Affinity labeling in situ of the Thermus thermophilus elongation factor Tu (EF-Tu) nucleotide binding site was achieved with periodate-oxidized GDP (GDPoxi) or GTP (GTPoxi) in the absence and presence of elongation factor Ts (EF-Ts). Lys52 and Lys137, both reacting with GDPoxi and GTPoxi, are located in the nucleotide binding region. In the absence of EF-Ts Lys137 and to a lesser extent Lys52 were accessible to the reaction with GTPoxi, GDPoxi reacted much more efficiently with Lys52 than with Lys137 under these conditions [Peter, M. E., Wittman-Liebold, B. & Sprinzl, M. (1988) Biochemistry 27, 9132–9138]. In the presence of EF-Ts, GDPoxi reacted more efficiently with Lys137 than with Lys52, indicating that the interaction of EF-Ts with EF-Tu˙ GDPoxi induces a conformation resembling that of the EF-Tu˙ GTPoxi complex in the absence of EF-Ts. Binding of EF-Ts to EF-Tu˙ GDP enhances the accessibility of the Arg59-Gly60 peptide bond of EF-Tu to trypsin cleavage. Hydrolysis of this peptide bond does not interfere with the ability of EF-Ts to bind to EF-Ts. EF-Ts is protected against trypsin cleavage by interaction with EF-Tu˙ GDP. High concentrations of EF-Ts did not interfere significantly with aminoacyl-tRNA˙ EF–Tu˙ GTP complex formation.