Schlecker Tanja, Schmidt Armin, Dirdjaja Natalie, Voncken Frank, Clayton Christine, Krauth-Siegel R Luise
Biochemie-Zentrum der Universität Heidelberg, Germany.
J Biol Chem. 2005 Apr 15;280(15):14385-94. doi: 10.1074/jbc.M413338200. Epub 2005 Jan 21.
Trypanosoma brucei, the causative agent of African sleeping sickness, encodes three nearly identical cysteine homologues of the classical selenocysteine-containing glutathione peroxidases. Although one of the sequences, peroxidase III, carries both putative mitochondrial and glycosomal targeting signals, the proteins are detectable only in the cytosol and mitochondrion of mammalian bloodstream and insect procyclic T. brucei. The enzyme is a trypanothione/tryparedoxin peroxidase as are the 2 Cys-peroxiredoxins of the parasite. Hydrogen peroxide, thymine hydroperoxide, and linoleic acid hydroperoxide are reduced with second order rate constants of 8.7 x 10(4), 7.6 x 10(4), and 4 x 10(4) m(-1) s(-1), respectively, and represent probable physiological substrates. Phosphatidylcholine hydroperoxide is a very weak substrate and, in the absence of Triton X-100, even an inhibitor of the enzyme. The substrate preference clearly contrasts with that of the closely related T. cruzi enzyme, which reduces phosphatidylcholine hydroperoxides but not H(2)O(2). RNA interference causes severe growth defects in bloodstream and procyclic cells in accordance with the peroxidases being essential in both developmental stages. Thus, the cellular functions of the glutathione peroxidase-type enzymes cannot be taken over by the 2 Cys-peroxiredoxins that also occur in the cytosol and mitochondrion of the parasite.
布氏锥虫是非洲昏睡病的病原体，它编码三种与经典含硒半胱氨酸的谷胱甘肽过氧化物酶几乎相同的半胱氨酸同系物。尽管其中一个序列，即过氧化物酶III，同时携带假定的线粒体和糖体靶向信号，但这些蛋白质仅在哺乳动物血液期和昆虫前循环期布氏锥虫的细胞质和线粒体中可检测到。该酶是一种锥虫硫醇/锥虫硫氧还蛋白过氧化物酶，就像该寄生虫的2种半胱氨酸过氧化物酶一样。过氧化氢、胸腺嘧啶过氧化氢和亚油酸过氧化氢的还原二级速率常数分别为8.7×10⁴、7.6×10⁴和4×10⁴ m⁻¹ s⁻¹，它们可能是生理底物。磷脂酰胆碱过氧化氢是一种非常弱的底物，在没有 Triton X - 100的情况下，甚至是该酶的抑制剂。这种底物偏好与密切相关的克氏锥虫酶明显不同，后者可还原磷脂酰胆碱过氧化氢但不能还原H₂O₂。RNA干扰会导致血液期和前循环期细胞出现严重的生长缺陷，这与过氧化物酶在两个发育阶段都必不可少一致。因此，谷胱甘肽过氧化物酶类型的酶的细胞功能不能被同样存在于寄生虫细胞质和线粒体中的2种半胱氨酸过氧化物酶所取代。
