PMID:11970956

Citation	Kitabatake, M, Ali, K, Demain, A, Sakamoto, K, Yokoyama, S and Söll, D (2002) Indolmycin resistance of Streptomyces coelicolor A3(2) by induced expression of one of its two tryptophanyl-tRNA synthetases. J. Biol. Chem. 277:23882-7
Abstract	Aminoacyl-tRNA synthetases, a family of enzymes essential for protein synthesis, are promising targets of antimicrobials. Indolmycin, a secondary metabolite of Streptomyces griseus and a selective inhibitor of prokaryotic tryptophanyl-tRNA synthetase (TrpRS), was used to explore the mechanism of inhibition and to explain the resistance of a naturally occurring strain. Streptomyces coelicolor A3(2), an indolmycin-resistant strain, contains two trpS genes encoding distinct TrpRS enzymes. We show that TrpRS1 is indolmycin-resistant in vitro and in vivo, whereas TrpRS2 is sensitive. The lysine (position 9) in the enzyme tryptophan binding site is essential for making TrpRS1 indolmycin-resistant. Replacement of lysine 9 by glutamine, which at this position is conserved in most bacterial TrpRS proteins, abolished the ability of the mutant trpS gene to confer indolmycin resistance in vivo. Molecular modeling suggests that lysine 9 sterically hinders indolmycin binding to the enzyme. Tryptophan recognition (assessed by k(cat)/K(M)) by TrpRS1 is 4-fold lower than that of TrpRS2. Examination of the mRNA for the two enzymes revealed that only TrpRS2 mRNA is constitutively expressed, whereas mRNA for the indolmycin-resistant TrpRS1 enzyme is induced when the cells are exposed to indolmycin.
Links	PubMed Online version:10.1074/jbc.M202639200
Keywords	Amino Acid Sequence; Anti-Bacterial Agents/pharmacology; Cloning, Molecular; Drug Resistance, Bacterial; Indoles/pharmacology; Isoenzymes/analysis; Isoenzymes/genetics; Models, Structural; Molecular Sequence Data; RNA, Messenger/analysis; Sequence Alignment; Streptomyces/drug effects; Tryptophan-tRNA Ligase/analysis; Tryptophan-tRNA Ligase/chemistry; Tryptophan-tRNA Ligase/genetics
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