Bang Iel-Soo, Liu Limin, Vazquez-Torres Andrés, Crouch Marie-Laure, Stamler Jonathan S, Fang Ferric C
Departments of Microbiology and Laboratory Medicine, University of Washington School of Medicine, Seattle, 98195, USA.
J Biol Chem. 2006 Sep 22;281(38):28039-47. doi: 10.1074/jbc.M605174200. Epub 2006 Jul 26.
Intracellular pathogens must resist the antimicrobial actions of nitric oxide (NO.) produced by host cells. To this end pathogens possess several NO.-metabolizing enzymes. Here we show that the flavohemoglobin Hmp is the principal enzyme responsible for aerobic NO. metabolism by Salmonella enterica serovar typhimurium. We further show that Hmp is required for Salmonella virulence in mice, in contrast to S-nitrosoglutathione reductase, flavorubredoxin, or cytochrome c nitrite reductase. Abrogation of murine-inducible NO. synthase restores virulence to hmp mutant bacteria. In the presence of nitrosative stress, Hmp-deficient Salmonella exhibits reduced NO. consumption, impaired growth, increased protein S-nitrosylation, and filamentous morphology. However, under aerobic conditions in the absence of nitrosative stress, elevated hmp expression increases S. typhimurium susceptibility to hydrogen peroxide. Both the heme binding and flavoreductase domains are required for resistance to NO., whereas the flavoreductase domain is responsible for iron-dependent susceptibility to oxidative stress. This provides a rationale for the regulation of hmp expression by the transcriptional repressor NsrR in response to both nitrosative stress and intracellular free iron concentration. The Hmp flavohemoglobin plays a central role in the response of Salmonella to nitrosative stress but requires precise regulation to avoid the exacerbation of oxidative stress that can result if electrons are shuttled to extraneous iron.
细胞内病原体必须抵抗宿主细胞产生的一氧化氮（NO·）的抗菌作用。为此，病原体拥有几种代谢NO·的酶。在这里，我们表明黄素血红蛋白Hmp是鼠伤寒沙门氏菌有氧代谢NO·的主要酶。我们进一步表明，与S-亚硝基谷胱甘肽还原酶、黄素铁氧化还原蛋白或细胞色素c亚硝酸盐还原酶不同，Hmp是小鼠体内沙门氏菌毒力所必需的。消除小鼠诱导型NO合酶可恢复hmp突变细菌的毒力。在存在亚硝化应激的情况下，缺乏Hmp的沙门氏菌表现出NO·消耗减少、生长受损、蛋白质S-亚硝基化增加和丝状形态。然而，在没有亚硝化应激的有氧条件下，hmp表达升高会增加鼠伤寒沙门氏菌对过氧化氢的敏感性。抗NO·需要血红素结合域和黄素还原酶域，而黄素还原酶域负责铁依赖性氧化应激敏感性。这为转录阻遏物NsrR响应亚硝化应激和细胞内游离铁浓度调节hmp表达提供了理论依据。Hmp黄素血红蛋白在沙门氏菌对亚硝化应激的反应中起核心作用，但需要精确调节以避免如果电子转移到外来铁可能导致的氧化应激加剧。
