Conformational Transition in Polypeptide Elongation Factor Tu as Revealed by Electron Spin Resonance

The conformational transition in the polypeptide elongation factor Tu (EF-Tu) associated with the ligand change from GTP to GDP has been suggested from the differences in their reactivity toward aminoacyl-tRNA. We have examined the structural changes in these two forms of EF-Tu near the active site interacting with aminoacyl-tRNA using the protein spin-labeled with N-ethylmaleimide analogues. It was found that, among three sulfhydryl groups of EF-Tu, the one essential for the binding of aminoacyl-tRNA could be labeled specifically in the presence of GDP. The electron spin resonance spectra of the spin-labeled EF-Tu GDP complex markedly changed when its GDP moiety was replaced by GTP by incubation with phosphoenolpyruvate and pyruvate kinase. The spectral changes unequivocally demonstrate that a reversible conformational change does occur in EF-Tu near the active site induced by the ligand conversion from GDP to GTP.