Bonilla Mariana, Krull Erika, Irigoín Florencia, Salinas Gustavo, Comini Marcelo A
Redox Biology of Trypanosomes Laboratory, Institut Pasteur de Montevideo, Uruguay.
Molecular Human Genetics Laboratory, Institut Pasteur de Montevideo, Uruguay; Departamento de Histología y Embriología, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
Mol Biochem Parasitol. 2016 Mar-Apr;206(1-2):13-9. doi: 10.1016/j.molbiopara.2016.03.002. Epub 2016 Mar 11.
The trace element selenium is found in polypeptides as selenocysteine, the 21(st) amino acid that is co-translationally inserted into proteins at a UGA codon. In proteins, selenocysteine usually plays a role as an efficient redox catalyst. Trypanosomatids previously examined harbor a full set of genes encoding the machinery needed for selenocysteine biosynthesis and incorporation into three selenoproteins: SelK, SelT and, the parasite-specific, Seltryp. We investigated the selenoproteome of kinetoplastid species in recently sequenced genomes and assessed the in vivo relevance of selenoproteins for African trypanosomes. Database mining revealed that SelK, SelT and Seltryp genes are present in most kinetoplastids, including the free-living species Bodo saltans, and Seltryp was lost in the subgenus Viannia from the New World Leishmania. Homology and sinteny with bacterial sulfur dioxygenases and sulfur transferases suggest a putative role for Seltryp in sulfur metabolism. A Trypanosoma brucei selenocysteine synthase (SepSecS) null-mutant, in which selenoprotein synthesis is abolished, displayed similar sensitivity to oxidative stress induced by a short-term exposure to high concentrations of methylglyoxal or H2O2 to that of the parental wild-type cell line. Importantly, the infectivity of the SepSecS knockout cell line was not impaired when tested in a mouse infection model and compensatory effects via up-regulation of proteins involved in thiol-redox metabolism were not observed. Collectively, our data show that selenoproteins are not required for survival of African trypanosomes in a mammalian host and exclude a role for selenoproteins in parasite antioxidant defense and/or virulence. On this basis, selenoproteins can be disregarded as drug target candidates.
微量元素硒以硒代半胱氨酸的形式存在于多肽中，硒代半胱氨酸是第21种氨基酸，它在翻译过程中通过UGA密码子共翻译插入到蛋白质中。在蛋白质中，硒代半胱氨酸通常作为一种高效的氧化还原催化剂发挥作用。先前研究的锥虫含有一整套基因，这些基因编码硒代半胱氨酸生物合成以及将其掺入三种硒蛋白所需的机制：SelK、SelT以及寄生虫特异性的Seltryp。我们研究了近期测序基因组中动基体物种的硒蛋白组，并评估了硒蛋白对非洲锥虫的体内相关性。数据库挖掘显示，SelK、SelT和Seltryp基因存在于大多数动基体中，包括自由生活的物种盐沼波豆虫，而Seltryp在新世界利什曼原虫的维安亚属中丢失。与细菌硫双加氧酶和硫转移酶的同源性和共线性表明Seltryp在硫代谢中可能发挥作用。布氏锥虫硒代半胱氨酸合成酶（SepSecS）基因敲除突变体中，硒蛋白合成被废除，与亲本野生型细胞系相比，在短期暴露于高浓度甲基乙二醛或过氧化氢诱导的氧化应激下表现出相似的敏感性。重要的是，在小鼠感染模型中测试时，SepSecS基因敲除细胞系的感染性没有受损，也未观察到通过上调参与硫醇-氧化还原代谢的蛋白质产生的补偿作用。总体而言，我们的数据表明，硒蛋白对于非洲锥虫在哺乳动物宿主中的存活不是必需的，并且排除了硒蛋白在寄生虫抗氧化防御和/或毒力中的作用。在此基础上，硒蛋白可以被视为药物靶点候选物而不予考虑。
