Noguchi Fumiya, Shimamura Shigeru, Nakayama Takuro, Yazaki Euki, Yabuki Akinori, Hashimoto Tetsuo, Inagaki Yuji, Fujikura Katsunori, Takishita Kiyotaka
Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Minato-ku, Tokyo, Japan; Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa, Japan.
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa, Japan.
Protist. 2015 Nov;166(5):534-50. doi: 10.1016/j.protis.2015.08.002. Epub 2015 Aug 29.
Functionally and morphologically degenerate mitochondria, so-called mitochondrion-related organelles (MROs), are frequently found in eukaryotes inhabiting hypoxic or anoxic environments. In the last decade, MROs have been discovered from a phylogenetically broad range of eukaryotic lineages and these organelles have been revealed to possess diverse metabolic capacities. In this study, the biochemical characteristics of an MRO in the free-living anaerobic protist Cantina marsupialis, which represents an independent lineage in stramenopiles, were inferred based on RNA-seq data. We found transcripts for proteins known to function in one form of MROs, the hydrogenosome, such as pyruvate:ferredoxin oxidoreductase, iron-hydrogenase, acetate:succinate CoA-transferase, and succinyl-CoA synthase, along with transcripts for acetyl-CoA synthetase (ADP-forming). These proteins possess putative mitochondrial targeting signals at their N-termini, suggesting dual ATP generation systems through anaerobic pyruvate metabolism in Cantina MROs. In addition, MROs in Cantina were also shown to share several features with canonical mitochondria, including amino acid metabolism and an "incomplete" tricarboxylic acid cycle. Transcripts for all four subunits of complex II (CII) of the electron transport chain were detected, while there was no evidence for the presence of complexes I, III, IV, or F1Fo ATPase. Cantina MRO biochemistry challenges the categories of mitochondrial organelles recently proposed.
功能和形态上退化的线粒体，即所谓的线粒体相关细胞器（MROs），在栖息于缺氧或无氧环境的真核生物中经常被发现。在过去十年中，已从系统发育范围广泛的真核生物谱系中发现了MROs，并且这些细胞器已被揭示具有多种代谢能力。在本研究中，基于RNA测序数据推断了自由生活的厌氧原生生物袋形坎氏虫（Cantina marsupialis）中MRO的生化特征，该原生生物代表了不等鞭毛类中的一个独立谱系。我们发现了已知在一种形式的MRO即氢化酶体中发挥作用的蛋白质的转录本，例如丙酮酸：铁氧化还原蛋白氧化还原酶、铁氢化酶、乙酸盐：琥珀酸辅酶A转移酶和琥珀酰辅酶A合成酶，以及ADP形成型乙酰辅酶A合成酶的转录本。这些蛋白质在其N末端具有推定的线粒体靶向信号，表明袋形坎氏虫的MROs通过厌氧丙酮酸代谢存在双重ATP生成系统。此外，还表明袋形坎氏虫中的MROs与典型线粒体具有一些共同特征，包括氨基酸代谢和“不完全”三羧酸循环。检测到了电子传递链复合物II（CII）所有四个亚基的转录本，而没有证据表明存在复合物I、III、IV或F1Fo ATP酶。袋形坎氏虫MRO的生物化学对最近提出的线粒体细胞器类别提出了挑战。
