title: Inhibition of Mycobacterium tuberculosis AhpD, an element of the peroxiredoxin defense against oxidative stress.
abstract: The resistance of Mycobacterium tuberculosis to isoniazid (INH) is largely linked to suppression of a catalase-peroxidase enzyme (KatG) that activates INH. In the absence of KatG, antioxidant protection is provided by enhanced expression of the peroxiredoxin AhpC, which is itself reduced by AhpD, a protein with low alkylhydroperoxidase activity of its own. Inhibition of AhpD might therefore impair the antioxidant protection afforded by AhpC and make KatG-negative strains more sensitive to oxidative stress. We report here that the 3(E),17-dioxime of testosterone is a potent competitive AhpD inhibitor, with a K(i) of 50 +/- 2 nM. The inhibitor is stereospecific, in that the 3(E) but not 3(Z) isomer is active. Computational studies provide support for a proposed AhpD substrate binding site. However, the inhibitor does not completely suppress the in vitro activity of AhpC/AhpD, because a low titer of AhpD suffices to maintain AhpC activity. This finding, and the low solubility of the inhibitor, explains its inability to suppress the growth of INH-resistant M. tuberculosis in infected mouse lungs.
authors.affiliation: University of California, Genentech Hall N572D, 600 16th Street, San Francisco, CA 94143-2280, USA.
authors.forename: Aleksey
authors.initials: A
authors.lastname: Koshkin
authors.forename: Xiao-ti
authors.initials: XT
authors.lastname: Zhou
authors.forename: Carl N
authors.initials: CN
authors.lastname: Kraus
authors.forename: Jason M
authors.initials: JM
authors.lastname: Brenner
authors.forename: Pradipta
authors.initials: P
authors.lastname: Bandyopadhyay
authors.forename: Irwin D
authors.initials: ID
authors.lastname: Kuntz
authors.forename: Clifton E
authors.initials: CE
authors.lastname: Barry
authors.forename: Paul R
authors.initials: PR
authors.lastname: Ortiz de Montellano
mesh_terms: D000818:Animals; D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins; D015169:Colony Count, Microbial; D005260:Female; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D018384:Oxidative Stress / Q000187:drug effects*; D010544:Peroxidases / Q000032:analysis* / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology*; D054464:Peroxiredoxins; D013261:Sterols / Q000378:metabolism
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D013261:Sterols; D006861:Hydrogen Peroxide; C489153:AhpD protein, Mycobacterium tuberculosis; D010544:Peroxidases; D054464:Peroxiredoxins