title: The interaction of fusidic acid with peptidyl-transfer-ribonucleic-acid - ribosome complexes.
abstract: The inhibitory action of fusidic acid on peptide-chain elongation was studied with systems in vitro directed by either polyuridylic acid or endogenous messenger (Escherichia coli polysomes washed with 1 M NH4Cl) or R17 RNA, and supplemented with either crude or purified elongation factors. In all cases strong inhibition of synthesis required high concentrations of the antibiotic (approx. 1 mM), while a similar inhibition of the EF-G-plus-ribosome-dependent GTP hydrolysis required between 10 and 100 times less antibiotic. Since most of the GTP hydrolysis observed was presumably due to free ribosomes (without aminoacyl-tRNA or peptidyl-tRNA), fusidic acid seemed to interact far more easily with these ribosomes than with ribosomes engaged in peptide-chain elongation. The role of the GDP-EF-G-ribosome-fusidic acid complex in the inhibition of polypeptide synthesis was assessed by measuring formation of this complex on polysomes engaged in peptide-chain elongation. Using purified elongation factors the complex formed on only 25-35% of ribosomes, as measured either by retention of [3H]GDP or by hydrolysis of [3H, gamma-32P]GTP. In contrast, with crude factors (S 100 extract) it formed on more than 70% of ribosomes. The results are compatible with the postulated role of the complex in polypeptide synthesis inhibition (blockade of the ribosomal acceptor site and subsequent inhibition of aminoacyl-tRNA binding) and indicate that formation of the complex takes place by overriding the control that prevents interaction of EF-G when the donor site is occupied by peptidyl-tRNA. In the polyuridylic-acid-directed system for synthesis of oligophenylalanine the antibiotic inhibits every round of peptide elongation, including dipeptide formation, to roughly the same extent.
mesh_terms: D001665:Binding Sites; D004926:Escherichia coli / Q000378:metabolism*; D005672:Fusidic Acid / Q000494:pharmacology*; D046911:Macromolecular Substances; D010441:Peptide Chain Elongation, Translational / Q000187:drug effects*; D010445:Peptide Elongation Factors; D010649:Phenylalanine / Q000378:metabolism; D011072:Poly U; D011485:Protein Binding; D012343:RNA, Transfer / Q000378:metabolism*; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D010445:Peptide Elongation Factors; D011072:Poly U; D010649:Phenylalanine; D005672:Fusidic Acid; D012343:RNA, Transfer