Comini Marcelo A, Krauth-Siegel R Luise, Flohé Leopold
Centre of Biochemistry, Heidelberg University, Im Neuenheimer Feld 504, D-69120, Heidelberg, Germany.
Biochem J. 2007 Feb 15;402(1):43-9. doi: 10.1042/BJ20061341.
In trypanosomes, the thioredoxin-type protein TXN (tryparedoxin) is a multi-purpose oxidoreductase that is involved in the detoxification of hydroperoxides, the synthesis of DNA precursors and the replication of the kinetoplastid DNA. African trypanosomes possess two isoforms that are localized in the cytosol and in the mitochondrion of the parasites respectively. Here we report on the biological significance of the cTXN (cytosolic TXN) of Trypanosoma brucei for hydroperoxide detoxification. Depending on the growth phase, the concentration of the protein is 3-7-fold higher in the parasite form infecting mammals (50-100 microM) than in the form hosted by the tsetse fly (7-34 microM). Depletion of the mRNA in bloodstream trypanosomes by RNA interference revealed the indispensability of the protein. Proliferation and viability of cultured trypanosomes were impaired when TXN was lowered to 1 muM for more than 48 h. Although the levels of glutathione, glutathionylspermidine and trypanothione were increased 2-3.5-fold, the sensitivity against exogenously generated H2O2 was significantly enhanced. The results prove the essential role of the cTXN and its pivotal function in the parasite defence against oxidative stress.
在锥虫中，硫氧还蛋白型蛋白TXN（锥虫硫氧还蛋白）是一种多功能氧化还原酶，参与过氧化氢的解毒、DNA前体的合成以及动基体DNA的复制。非洲锥虫有两种亚型，分别定位于寄生虫的胞质溶胶和线粒体中。在此，我们报道布氏锥虫的胞质TXN（cTXN）在过氧化氢解毒中的生物学意义。根据生长阶段，感染哺乳动物的寄生虫形式中该蛋白的浓度（50 - 100 microM）比采采蝇体内的寄生虫形式（7 - 34 microM）高3 - 7倍。通过RNA干扰使血流中锥虫的mRNA耗竭，揭示了该蛋白的不可或缺性。当TXN降低至1 microM超过48小时时，培养的锥虫的增殖和活力受到损害。尽管谷胱甘肽、谷胱甘肽亚精胺和锥虫硫醇的水平增加了2 - 3.5倍，但对外源性产生的H2O2的敏感性显著增强。结果证明了cTXN的重要作用及其在寄生虫抵御氧化应激中的关键功能。
