Indole Propionic Acid Disturbs the Normal Function of Tryptophanyl-tRNA Synthetase in .

Tuberculosis (TB) is the leading infectious disease caused by and the second-most contagious killer after COVID-19. The emergence of drug-resistant TB has caused a great need to identify and develop new anti-TB drugs with novel targets. Indole propionic acid (IPA), a structural analog of tryptophan (Trp), is active against and . It has been verified that IPA exerts its antimicrobial effect by mimicking Trp as an allosteric inhibitor of TrpE, which is the first enzyme in the Trp synthesis pathway of . However, other Trp structural analogs, such as indolmycin, also target tryptophanyl-tRNA synthetase (TrpRS), which has two functions in bacteria: synthesis of tryptophanyl-AMP by catalyzing ATP + Trp and producing Trp-tRNA by transferring Trp to tRNA. So, we speculate that IPA may also target TrpRS. In this study, we found that IPA can dock into the Trp binding pocket of TrpRS (TrpRS), which was further confirmed by isothermal titration calorimetry (ITC) assay. The biochemical analysis proved that TrpRS can catalyze the reaction between IPA and ATP to generate pyrophosphate (PPi) without Trp as a substrate. Overexpression of wild-type in increased the MIC of IPA to 32-fold, and knock-down in made it more sensitive to IPA. The supplementation of Trp in the medium abrogated the inhibition of by IPA. We demonstrated that IPA can interfere with the function of TrpRS by mimicking Trp, thereby impeding protein synthesis and exerting its anti-TB effect.