Kirromycin, an Inhibitor of Protein Biosynthesis that Acts on Elongation Factor Tu

Abstract

Kirromycin, a new inhibitor of protein synthesis, is shown to interfere with the peptide transfer reaction by acting on elongation factor Tu (EF-Tu). All the reactions associated with this elongation factor are affected. Formation of the EF-Tu.GTP complex is strongly stimulated. Peptide bond formation is prevented only when Phe-tRNA(Phe) is bound enzymatically to ribosomes, presumably because GTP hydrolysis associated with enzymatic binding of Phe-tRNA(Phe) is not followed by release of EF-Tu.GDP from the ribosome. This antibiotic also enables EF-Tu to catalyze the binding of Phe-tRNA(Phe) to the poly(U).ribosome complex even in the absence of GTP. EF-Tu activity in the GTPase reaction is dramatically affected by kirromycin: GTP hydrolysis, which normally requires ribosomes and aminoacyl-tRNA, takes place with the elongation factor alone. This GTPase shows the same K(m) for GTP as the one dependent on Phe-tRNA(Phe) and ribosomes in the absence of the antibiotic. Ribosomes and Phe-tRNA(Phe), but not tRNA(Phe) or Ac-Phe-tRNA(Phe), stimulate the kirromycin-induced EF-Tu GTPase. These results indicate that the catalytic center of EF-Tu GTPase that is dependent upon aminoacyl-tRNA and ribosomes is primarily located on the elongation factor. In conclusion, kirromycin can substitute for GTP, aminoacyl-tRNA, or ribosomes in various reactions involving EF-Tu, apparently by affecting the allosteric controls between the sites on the EF-Tu molecule interacting with these components.