Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
Arch Biochem Biophys. 2011 Mar 15;507(2):287-95. doi: 10.1016/j.abb.2010.12.014. Epub 2010 Dec 16.
During host cell infection, Trypanosoma cruzi parasites are exposed to reactive oxygen and nitrogen species. As part of their antioxidant defense systems, they express two tryparedoxin peroxidases (TXNPx), thiol-dependent peroxidases members of the peroxiredoxin family. In this work, we report a kinetic characterization of cytosolic (c-TXNPx) and mitochondrial (m-TXNPx) tryparedoxin peroxidases from T. cruzi. Both c-TXNPx and m-TXNPx rapidly reduced hydrogen peroxide (k=3.0 x 10⁷ and 6 x 10⁶ M⁻¹ s⁻¹ at pH 7.4 and 25 °C, respectively) and peroxynitrite (k=1.0 x 10⁶ and k=1.8 x 10⁷ M⁻¹ s⁻¹ at pH 7.4 and 25 °C, respectively). The reductive part of the catalytic cycle was also studied, and the rate constant for the reduction of c-TXNPx by tryparedoxin I was 1.3 x 10⁶ M⁻¹ s⁻¹. The catalytic role of two conserved cysteine residues in both TXNPxs was confirmed with the identification of Cys52 and Cys173 (in c-TXNPX) and Cys81 and Cys204 (in m-TXNPx) as the peroxidatic and resolving cysteines, respectively. Our results indicate that mitochondrial and cytosolic TXNPxs from T. cruzi are highly efficient peroxidases that reduce hydrogen peroxide and peroxynitrite, and contribute to the understanding of their role as virulence factors reported in vivo.
在宿主细胞感染期间，克氏锥虫寄生虫暴露于活性氧和氮物种中。作为其抗氧化防御系统的一部分，它们表达两种硫氧还蛋白过氧化物酶（TXNPx），即过氧化物酶家族中的硫醇依赖性过氧化物酶。在这项工作中，我们报告了来自克氏锥虫的细胞质（c-TXNPx）和线粒体（m-TXNPx）硫氧还蛋白过氧化物酶的动力学特征。c-TXNPx 和 m-TXNPx 都能迅速还原过氧化氢（在 pH 7.4 和 25°C 时的 k 值分别为 3.0 x 10⁷ 和 6 x 10⁶ M⁻¹ s⁻¹）和过氧亚硝酸盐（在 pH 7.4 和 25°C 时的 k 值分别为 1.0 x 10⁶ 和 1.8 x 10⁷ M⁻¹ s⁻¹）。还研究了催化循环的还原部分，并且 tryparedoxin I 还原 c-TXNPx 的速率常数为 1.3 x 10⁶ M⁻¹ s⁻¹。通过鉴定 Cys52 和 Cys173（在 c-TXNPX 中）和 Cys81 和 Cys204（在 m-TXNPx 中）作为过氧和解析半胱氨酸，证实了两个保守半胱氨酸残基在两个 TXNPxs 中的催化作用。我们的结果表明，来自克氏锥虫的线粒体和细胞质 TXNPxs 是高效的过氧化物酶，可还原过氧化氢和过氧亚硝酸盐，并有助于理解其作为体内报道的毒力因子的作用。
