Abstract
New drugs and new targets are urgently needed to treat tuberculosis. We discovered the D-phenylalanine-benzoxazole Q112 displays potent antibacterial activity against Mycobacterium tuberculosis in multiple media and in macrophage infections. Metabolomic profiling experiments indicate that Q112 has a unique mechanism of action compared to other antitubercular agents. Q112 perturbs the essential pantothenate/CoA biosynthetic pathway, depleting pantoate while increasing ketopantoate, as would be expected if ketopantoate reductase (KPR) were inhibited. We searched for alternative KPRs since the canonical enzyme is not essential in Mtb. The ketol-acid reductoisomerase IlvC catalyzes the KPR reaction in the close Mtb relative Corynebacterium glutamicum, but Mtb IlvC does not display KPR activity. We identified the essential protein Rv3603c as an ortholog of the second alternative KPR PanG, and purified recombinant Rv3603c is a bona fide PanG KPR. Q112 inhibits Rv3603c, explaining the metabolomic changes. Surprisingly, pantothenate does not rescue Q112-treated bacteria, indicating that Q112 has an additional target(s).