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Structure of F420 binding protein Rv1558 from Mycobacterium tuberculosis with F420 boundStructure of F420 binding protein Rv1558 from Mycobacterium tuberculosis with F420 bound
Structural highlights
FunctionFQR58_MYCTU Involved in a F420-dependent anti-oxidant mechanism that protects M.tuberculosis against oxidative stress and bactericidal agents. Catalyzes the F420H(2)-dependent two-electron reduction of quinones to dihydroquinones, thereby preventing the formation of cytotoxic semiquinones obtained by the one-electron reduction pathway. In vitro, catalyzes the reduction of menadione to menadiol; since menaquinone is the sole quinone electron carrier in the respiratory chain in M.tuberculosis, the physiological electron acceptor for Fqr-mediated F420H(2) oxidation is therefore likely to be the endogenous menaquinone found in the membrane fraction of M.tuberculosis.[1] Publication Abstract from PubMedTriaza-coumarin (TA-C) is a Mycobacterium tuberculosis (Mtb) dihydrofolate reductase (DHFR) inhibitor with an IC50 (half maximal inhibitory concentration) of approximately 1 microM against the enzyme. Despite this moderate target inhibition, TA-C shows exquisite antimycobacterial activity (MIC50, concentration inhibiting growth by 50% = 10 to 20 nM). Here, we investigated the mechanism underlying this potency disconnect. To confirm that TA-C targets DHFR and investigate its unusual potency pattern, we focused on resistance mechanisms. In Mtb, resistance to DHFR inhibitors is frequently associated with mutations in thymidylate synthase thyA, which sensitizes Mtb to DHFR inhibition, rather than in DHFR itself. We observed thyA mutations, consistent with TA-C interfering with the folate pathway. A second resistance mechanism involved biosynthesis of the redox coenzyme F420 Thus, we hypothesized that TA-C may be metabolized by Mtb F420-dependent oxidoreductases (FDORs). By chemically blocking the putative site of FDOR-mediated reduction in TA-C, we reproduced the F420-dependent resistance phenotype, suggesting that F420H2-dependent reduction is required for TA-C to exert its potent antibacterial activity. Indeed, chemically synthesized TA-C-Acid, the putative product of TA-C reduction, displayed a 100-fold lower IC50 against DHFR. Screening seven recombinant Mtb FDORs revealed that at least two of these enzymes reduce TA-C. This redundancy in activation explains why no mutations in the activating enzymes were identified in the resistance screen. Analysis of the reaction products confirmed that FDORs reduce TA-C at the predicted site, yielding TA-C-Acid. This work demonstrates that intrabacterial metabolism converts TA-C, a moderately active "prodrug," into a 100-fold-more-potent DHFR inhibitor, thus explaining the disconnect between enzymatic and whole-cell activity. Potency boost of a Mycobacterium tuberculosis dihydrofolate reductase inhibitor by multienzyme F420H2-dependent reduction.,Aragaw WW, Lee BM, Yang X, Zimmerman MD, Gengenbacher M, Dartois V, Chui WK, Jackson CJ, Dick T Proc Natl Acad Sci U S A. 2021 Jun 22;118(25). pii: 2025172118. doi:, 10.1073/pnas.2025172118. PMID:34161270[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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