Boxma Brigitte, de Graaf Rob M, van der Staay Georg W M, van Alen Theo A, Ricard Guenola, Gabaldón Toni, van Hoek Angela H A M, Moon-van der Staay Seung Yeo, Koopman Werner J H, van Hellemond Jaap J, Tielens Aloysius G M, Friedrich Thorsten, Veenhuis Marten, Huynen Martijn A, Hackstein Johannes H P
Department of Evolutionary Microbiology, Faculty of Science, Radboud University Nijmegen, Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands.
Nature. 2005 Mar 3;434(7029):74-9. doi: 10.1038/nature03343.
Hydrogenosomes are organelles that produce ATP and hydrogen, and are found in various unrelated eukaryotes, such as anaerobic flagellates, chytridiomycete fungi and ciliates. Although all of these organelles generate hydrogen, the hydrogenosomes from these organisms are structurally and metabolically quite different, just like mitochondria where large differences also exist. These differences have led to a continuing debate about the evolutionary origin of hydrogenosomes. Here we show that the hydrogenosomes of the anaerobic ciliate Nyctotherus ovalis, which thrives in the hindgut of cockroaches, have retained a rudimentary genome encoding components of a mitochondrial electron transport chain. Phylogenetic analyses reveal that those proteins cluster with their homologues from aerobic ciliates. In addition, several nucleus-encoded components of the mitochondrial proteome, such as pyruvate dehydrogenase and complex II, were identified. The N. ovalis hydrogenosome is sensitive to inhibitors of mitochondrial complex I and produces succinate as a major metabolic end product--biochemical traits typical of anaerobic mitochondria. The production of hydrogen, together with the presence of a genome encoding respiratory chain components, and biochemical features characteristic of anaerobic mitochondria, identify the N. ovalis organelle as a missing link between mitochondria and hydrogenosomes.
氢化酶体是产生三磷酸腺苷（ATP）和氢气的细胞器，存在于各种无亲缘关系的真核生物中，如厌氧鞭毛虫、壶菌纲真菌和纤毛虫。尽管所有这些细胞器都能产生氢气，但这些生物的氢化酶体在结构和代谢上有很大差异，就像线粒体也存在很大差异一样。这些差异引发了关于氢化酶体进化起源的持续争论。在这里，我们表明，在蟑螂后肠中茁壮生长的厌氧纤毛虫卵形夜毛虫的氢化酶体保留了一个编码线粒体电子传递链组分的原始基因组。系统发育分析表明，那些蛋白质与需氧纤毛虫的同源物聚集在一起。此外，还鉴定出线粒体蛋白质组的几个核编码组分，如丙酮酸脱氢酶和复合物II。卵形夜毛虫的氢化酶体对线粒体复合物I的抑制剂敏感，并产生琥珀酸作为主要代谢终产物——这是厌氧线粒体的典型生化特征。氢气的产生，加上编码呼吸链组分的基因组的存在，以及厌氧线粒体的生化特征，将卵形夜毛虫的细胞器确定为线粒体和氢化酶体之间缺失的环节。
