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Tuberculosis (TB) remains one of the leading causes of death due to a single pathogen. The emergence and proliferation of multidrug-resistant (MDR-TB) and extensively drug-resistant strains (XDR-TB) represent compelling reasons to invest in the pursuit of new anti-TB agents. The shikimate pathway, responsible for chorismate biosynthesis, which is a precursor of important aromatic compounds, is required for Mycobacterium tuberculosis growth. The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase ( Mtb DAHPS) catalyzes the first step in the shikimate pathway and it is an attractive target for anti-tubercular agents. Here, we used a CRISPRi system to evaluate the DAHPS as a vulnerable target in M. tuberculosis. The silencing of aroG significantly reduces the M. tuberculosis growth in both rich medium and, especially, in infected murine macrophages. The supplementation with amino acids was only able to partially rescue the growth of bacilli, whereas the Aro supplement (aromix) was enough to sustain the bacterial growth at lower rates. This study shows that Mtb DAHPS protein is vulnerable and, therefore, an attractive target to develop new anti-TB agents. In addition, the study contributes to a better understanding of the biosynthesis of aromatic compounds and the bacillus physiology. IMPORTANCE Determining the vulnerability of a potential target allows us to assess whether its partial inhibition will impact bacterial growth. Here, we evaluated the vulnerability of the enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAHPS) from M. tuberculosis by silencing the DAHPS-coding aroG gene in different contexts. These results could lead to the development of novel and potent anti-tubercular agents in the near future.

The epidemiological importance of mycobacterial species is indisputable, and the necessity to find new molecules that can inhibit their growth is urgent. The shikimate pathway, required for the synthesis of important bacterial metabolites, represents a set of targets for inhibitors of Mycobacterium tuberculosis growth. The aroA -encoded 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme catalyzes the sixth step of the shikimate pathway. In this study, we combined gene disruption, gene knockdown, point mutations (D61W, R134A, E321N), and kinetic analysis to evaluate aroA gene essentiality and vulnerability of its protein product, EPSPS, from Mycolicibacterium ( Mycobacterium ) smegmatis ( Ms EPSPS). We demonstrate that aroA -deficient cells are auxotrophic for aromatic amino acids (AroAAs) and that the growth impairment observed for aroA -knockdown cells grown on defined medium can be rescued by AroAA supplementation. We also evaluated the essentiality of selected Ms EPSPS residues in bacterial cells grown without AroAA supplementation. We found that the catalytic residues R134 and E321 are essential, while D61, presumably important for protein dynamics and suggested to have an indirect role in catalysis, is not essential under the growth conditions evaluated. We have also determined the catalytic efficiencies ( K cat / K m ) of recombinant wild-type (WT) and mutated versions of Ms EPSPS (D61W, R134A, E321N). Our results suggest that drug development efforts toward EPSPS inhibition may be ineffective if bacilli have access to external sources of AroAAs in the context of infection, which should be evaluated further. In the absence of AroAA supplementation, aroA from M. smegmatis is essential, its essentiality is dependent on Ms EPSPS activity, and Ms EPSPS is vulnerable. IMPORTANCE We found that cells from Mycobacterium smegmatis, a model organism safer and easier to study than the disease-causing mycobacterial species, when depleted of an enzyme from the shikimate pathway, are auxotrophic for the three aromatic amino acids (AroAAs) that serve as building blocks of cellular proteins: l-tryptophan, l-phenylalanine, and l-tyrosine. That supplementation with only AroAAs is sufficient to rescue viable cells with the shikimate pathway inactivated was unexpected, since this pathway produces an end product, chorismate, that is the starting compound of essential pathways other than the ones that produce AroAAs. The depleted enzyme, the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), catalyzes the sixth step of shikimate pathway. Depletion of this enzyme inside cells was performed by disrupting or silencing the EPSPS-encoding aroA gene. Finally, we evaluated the essentiality of specific residues from EPSPS that are important for its catalytic activity, determined with experiments of enzyme kinetics using recombinant EPSPS mutants.