Molecular and biochemical characterisation of a thioredoxin-linked thiolperoxidase system in the hydrogenosomes of the microaerophilic parasite Trichomonas vaginalis

滴虫病是全世界最流行的非病毒性性传播感染，每年有1.8亿例。与滴虫病有关的艾滋病毒感染风险的增加以及滴虫病治疗中最重要的药物甲硝唑的耐药性的出现，增加了详细研究滴虫，特别是其独特的产生ATP的细胞器--氢小体的必要性。氢基因组含有丙酮酸：铁氧还蛋白氧化还原酶和铁氢酶等氧敏感酶，通过氧诱导的超氧化物歧化酶主动消耗氧气并产生过氧化氢。奇怪的是，到目前为止，在细胞器中还没有发现能够还原过氧化氢或烷基过氧化氢的酶，这引发了一个问题，即这些高度有害的化合物是如何在氢小体中解毒的。在对阴道毛滴虫氢小体进行的蛋白质组学分析中，我们发现了两个新的蛋白质，它们与两种可能的原核过氧化物酶--红蛋白和小的质膜硫醇过氧化物酶TPx有很强的相似性，它们似乎在氧化应激下受到不同的调控。先前在许多原核生物中都发现了TPX和红蛋白，但在其他真核生物中没有发现，这表明原核生物对滴虫氢小体的氧解毒系统有重要的贡献。为了了解滴虫氢体氧化应激保护的机制，我们建议分析TPX及其可能的供电子系统硫氧还蛋白/硫氧还蛋白还原酶在氢体中的生化活性，以及这些蛋白在氧化应激下的转录和翻译调节。

With 180 million cases per year trichomoniasis is the most prevalent non-viral sexually transmitted infection world wide. The elevated risk of HIV infection connected to trichomoniasis and emergence of resistance to the most important drug in trichomoniasis treatment, metronidazole, has raised the need to study trichomonads, and especially their unique ATP-generating organelles, the hydrogenosomes, in detail. Hydrogenosomes, which harbour oxygen-sensitive enzymes like pyruvate:ferrodoxin oxidoreductase and Fe-hydrogenase, actively consume oxygen and produce H2O2 via oxygen-inducible Superoxide dismutase. Curiously, no enzymes capable of reducing H2O2 or alkyl peroxides have so far been identified in the organelles, raising the question how these highly deleterious compounds are detoxified in hydrogenosomes. In an ongoing proteome analysis of Trichomonas vaginalis hydrogenosomes we have identified two novel proteins with strong similarity to two putative prokaryotic peroxidases, rubrerythrin and the small periplasmic thiol peroxidase Tpx, which seem to be differentially regulated under oxidative stress. Both Tpx and rubrerythrin were previously found in many prokaryotes but not in other eukaryotes, suggesting a significant prokaryotic contribution to the oxygen-detoxification system of trichomonad hydrogenosomes. We propose to analyse the biochemical activity of Tpx and its putative electron-donating system thioredoxin/thioredoxin reductase in hydrogenosomes, as well as transcriptional and translational regulation of these proteins under oxidative stess, in oder to understand the mechanisms of oxidative stress protection in hydrogenosomes of trichomonads.