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

Tuberculosis (TB) is the leading infectious disease caused by Mycobacterium tuberculosis 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 M. tuberculosis in vitro and in vivo. 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 M. tuberculosis. 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-tRNATrp by transferring Trp to tRNATrp. So, we speculate that IPA may also target TrpRS. In this study, we found that IPA can dock into the Trp binding pocket of M. tuberculosis TrpRS (TrpRSMtb), 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 trpS in M. tuberculosis increased the MIC of IPA to 32-fold, and knock-down trpS in Mycolicibacterium smegmatis made it more sensitive to IPA. The supplementation of Trp in the medium abrogated the inhibition of M. tuberculosis 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.

Towards an Integrative Understanding of tRNA Aminoacylation-Diet-Host-Gut Microbiome Interactions in Neurodegeneration.

Transgenic mice used for Alzheimer's disease (AD) preclinical experiments do not recapitulate the human disease. In our models, the dietary tryptophan metabolite tryptamine produced by human gut microbiome induces tryptophanyl-tRNA synthetase (TrpRS) deficiency with consequent neurodegeneration in cells and mice. Dietary supplements, antibiotics and certain drugs increase tryptamine content in vivo. TrpRS catalyzes tryptophan attachment to tRNAtrp at initial step of protein biosynthesis. Tryptamine that easily crosses the blood-brain barrier induces vasculopathies, neurodegeneration and cell death via TrpRS competitive inhibition. TrpRS inhibitor tryptophanol produced by gut microbiome also induces neurodegeneration. TrpRS inhibition by tryptamine and its metabolites preventing tryptophan incorporation into proteins lead to protein biosynthesis impairment. Tryptophan, a least amino acid in food and proteins that cannot be synthesized by humans competes with frequent amino acids for the transport from blood to brain. Tryptophan is a vulnerable amino acid, which can be easily lost to protein biosynthesis. Some proteins marking neurodegenerative pathology, such as tau lack tryptophan. TrpRS exists in cytoplasmic (WARS) and mitochondrial (WARS2) forms. Pathogenic gene variants of both forms cause TrpRS deficiency with consequent intellectual and motor disabilities in humans. The diminished tryptophan-dependent protein biosynthesis in AD patients is a proof of our model-based disease concept.

Human tryptophanyl-tRNA synthetase binds with heme to enhance its aminoacylation activity.

Mammalian tryptophanyl-tRNA synthetases (TrpRSs) are Zn2+-binding proteins that catalyze the aminoacylation of tRNATrp. The cellular expression level of human TrpRS is highly upregulated by interferon-gamma (IFN-gamma). In this study, a heme biosynthesis inhibitor, succinylacetone (SA), was found to inhibit cellular TrpRS activity in IFN-gamma-activated cells without affecting TrpRS protein expression. In addition, supplementation of lysates from the SA-treated cells with hemin fully restored TrpRS activity to control levels. Biochemical analyses using purified TrpRS demonstrated that heme can interact strongly with Zn2+-depleted human full-length TrpRS with a stoichiometric heme:protein ratio of 1:1 to enhance the aminoacylation activity significantly. In contrast, the Zn2+-bound form of TrpRS did not bind heme. Further studies using site-directed mutagenesis clarified that the Zn2+-unbound human H130R mutant cannot bind heme. These results provide the first evidence of the involvement of heme in regulation of TrpRS aminoacylation activity. The regulation mechanism and its physiological roles are discussed.

In vitro and in vivo antibacterial activities of TAK-083, an agent for treatment of Helicobacter pylori infection.

The antibacterial activity of TAK-083 was tested against 54 clinical isolates of Helicobacter pylori and was compared with those of amoxicillin, clarithromycin, and metronidazole. The growth-inhibitory activity of TAK-083 was more potent than that of amoxicillin, clarithromycin, or metronidazole (the MICs at which 90% of the strains are inhibited were 0.031, 0.125, 64, and 8 microg/ml, respectively). The antibacterial activity of TAK-083 was highly selective against H. pylori; there was a >30-fold difference between the concentration of TAK-083 required to inhibit the growth of H. pylori and that required to inhibit the growth of common aerobic and anaerobic bacteria. Exposure of H. pylori strains to TAK-083 at the MIC or at a greater concentration resulted in an extensive loss of viability. When four H. pylori strains were successively subcultured in the medium containing subinhibitory concentrations of TAK-083, no significant change in the MICs of this compound was observed. TAK-083 strongly inhibited the formation of tryptophanyl-tRNA in H. pylori while exhibiting little effect on the same system in eukaryotes. TAK-083 was efficacious in the treatment of gastric infection caused by H. pylori in Mongolian gerbils. The results presented here indicate that TAK-083 is a promising candidate for the treatment of H. pylori infection.