A d‑Phenylalanine-Benzoxazole Derivative
Reveals the Role of the Essential Enzyme Rv3603c in the Pantothenate
Biosynthetic Pathway of Mycobacterium tuberculosis
posted on 2022-01-11, 19:38authored byMichael
J. Pepi, Shibin Chacko, Gary M. Marqus, Vinayak Singh, Zhe Wang, Kyle Planck, Ryan T. Cullinane, Penchala N. Meka, Deviprasad R. Gollapalli, Thomas R. Ioerger, Kyu Y. Rhee, Gregory D. Cuny, Helena I.M. Boshoff, Lizbeth Hedstrom
New drugs and new targets are urgently
needed to treat tuberculosis.
We discovered that d-phenylalanine-benzoxazole Q112 displays potent antibacterial activity against Mycobacterium
tuberculosis (Mtb) in multiple media and
in macrophage infections. A metabolomic profiling indicates that Q112 has a unique mechanism of action. Q112 perturbs
the essential pantothenate/coenzyme A biosynthetic pathway, depleting
pantoate while increasing ketopantoate, as would be expected if ketopantoate
reductase (KPR) were inhibited. We searched for alternative KPRs,
since the enzyme annotated as PanE KPR 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 orthologue
of PanG KPR and demonstrated that a purified recombinant Rv3603c has
KPR activity. Q112 inhibits Rv3603c, explaining the metabolomic
changes. Surprisingly, pantothenate does not rescue Q112-treated bacteria, indicating that Q112 has an additional
target(s). Q112-resistant strains contain loss-of-function
mutations in the twin arginine translocase TatABC, further underscoring Q112’s unique mechanism of action. Loss of TatABC causes
a severe fitness deficit attributed to changes in nutrient uptake,
suggesting that Q112 resistance may derive from a decrease
in uptake.