Euglena gracilis is a metabolically flexible, photosynthetic, and adaptable free-living protist of considerable environmental importance and biotechnological value. By label-free liquid chromatography tandem mass spectrometry, a total of 1,786 proteins were identified from the E. gracilis purified mitochondria, representing one of the largest mitochondrial proteomes so far described. Despite this apparent complexity, protein machinery responsible for the extensive RNA editing, splicing, and processing in the sister clades diplonemids and kinetoplastids is absent. This strongly suggests that the complex mechanisms of mitochondrial gene expression in diplonemids and kinetoplastids occurred late in euglenozoan evolution, arising independently. By contrast, the alternative oxidase pathway and numerous ribosomal subunits presumed to be specific for parasitic trypanosomes are present in E. gracilis. We investigated the evolution of unexplored protein families, including import complexes, cristae formation proteins, and translation termination factors, as well as canonical and unique metabolic pathways. We additionally compare this mitoproteome with the transcriptome of Eutreptiella gymnastica, illuminating conserved features of Euglenida mitochondria as well as those exclusive to E. gracilis. This is the first mitochondrial proteome of a free-living protist from the Excavata and one of few available for protists as a whole. This study alters our views of the evolution of the mitochondrion and indicates early emergence of complexity within euglenozoan mitochondria, independent of parasitism.

中文翻译：

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来自纤细眼虫的独特复杂线粒体蛋白质组。


眼虫是一种代谢灵活、能进行光合作用、适应性强的自由生活原生生物，具有相当大的环境重要性和生物技术价值。通过无标记液相色谱串联质谱法，从E. gracilis纯化的线粒体中鉴定出总共 1,786 个蛋白质，代表迄今为止描述的最大的线粒体蛋白质组之一。尽管表面上很复杂，但在姐妹进化枝双克隆和动质体中，负责广泛 RNA 编辑、剪接和加工的蛋白质机制却并不存在。这有力地表明，双克隆动物和动质体中线粒体基因表达的复杂机制发生在裸虫进化的晚期，独立出现。相比之下，细小锥虫中存在替代氧化酶途径和许多被认为对寄生锥虫具有特异性的核糖体亚基。我们研究了未探索的蛋白质家族的进化，包括输入复合物、嵴形成蛋白质和翻译终止因子，以及典型和独特的代谢途径。我们还将该线粒体蛋白质组与Eutreptiellagynastica的转录组进行了比较，阐明了 Euglenida 线粒体以及E. gracilis独有的保守特征。这是来自 Excavata 的第一个自由生活的原生生物线粒体蛋白质组，也是为数不多的可用于整个原生生物的线粒体蛋白质组之一。这项研究改变了我们对线粒体进化的看法，并表明裸虫线粒体内早期出现了复杂性，与寄生无关。