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.
摘要
结核分枝杆菌
结核分枝杆菌
对异烟
肼(INH)的耐药性在很大程度上与激活 INH 的
过氧化氢酶(KatG)被抑制有关。在 KatG 缺失的情况下,
过氧化氢过氧化物酶 AhpC 的表达增强可提供抗氧化保护,而 AhpC 本身会被 AhpD 还原,后者是一种自身烷基氢
过氧化物酶活性较低的蛋白质。因此,抑制 AhpD 可能会损害 AhpC 提供的抗氧化保护,使 KatG 阴性菌株对氧化应激更加敏感。我们在此报告 3(
E
),17-
睾酮二
肟是一种强效的 AhpD 竞争性
抑制剂,其 K
K
i
为 50 ± 2 nM。该
抑制剂具有立体特异性,即 3(
E
) 而非 3(
Z
) 异构体具有活性。计算研究为所提出的 AhpD 底物结合位点提供了支持。然而,
抑制剂并不能完全抑制 AhpC/AhpD 的体外活性,因为低滴度的 AhpD 足以维持 AhpC 的活性。这一发现以及
抑制剂的低溶解度解释了为什么它不能抑制耐 INH 结核杆菌的生长。
结核杆菌
在受感染小鼠肺部的生长。