Department Biologie I - Botanik, Ludwig-Maximilians-Universität München, Planegg-Martinsried, 82152, Germany.
Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
Plant Physiol. 2020 Oct;184(2):1042-1055. doi: 10.1104/pp.19.01248. Epub 2020 Aug 5.
In yeast () and human () mitochondria, Oxidase assembly protein1 (Oxa1) is the general insertase for protein insertion from the matrix side into the inner membrane while Cytochrome oxidase assembly protein18 (Cox18/Oxa2) is specifically involved in the topogenesis of the complex IV subunit, Cox2. Arabidopsis () mitochondria contain four OXA homologs: OXA1a, OXA1b, OXA2a, and OXA2b. OXA2a and OXA2b are unique members of the Oxa1 superfamily, in that they possess a tetratricopeptide repeat (TPR) domain at their C termini. Here, we determined the role of OXA2a by studying viable mutant plants generated by partial complementation of homozygous lethal transfer-DNA insertional mutants using the developmentally regulated () promoter. The plants displayed growth retardation due to a reduction in the steady-state abundances of both -type cytochromes, cytochrome and cytochrome The observed reduction in the steady-state abundance of complex III could be attributed to cytochrome being one of its subunits. Expression of a soluble heme lyase from an organism with cytochrome maturation system III could functionally complement the lack of OXA2a. This implies that OXA2a is required for the system I cytochrome maturation of Arabidopsis. Due to the interaction of OXA2a with Cytochrome maturation protein CcmF C-terminal-like protein (CCMF) in a yeast split-ubiquitin based interaction assay, we propose that OXA2a aids in the membrane insertion of CCMF, which is presumed to form the heme lyase component of the cytochrome maturation pathway. In contrast with the crucial role played by the TPR domain of OXA2b, the TPR domain of OXA2a is not essential for its functionality.
在酵母和人类线粒体中，氧化酶组装蛋白 1（Oxa1）是将蛋白质从基质侧插入内膜的通用插入酶，而细胞色素氧化酶组装蛋白 18（Cox18/Oxa2）则专门参与复合物 IV 亚基 Cox2 的拓扑发生。拟南芥线粒体含有四个 OXA 同源物：OXA1a、OXA1b、OXA2a 和 OXA2b。OXA2a 和 OXA2b 是 Oxa1 超家族的独特成员，因为它们在 C 端具有四肽重复（TPR）结构域。在这里，我们通过使用发育调节的启动子来研究纯合致死转移 DNA 插入突变体的部分互补产生的可行突变体植物，确定了 OXA2a 的作用。由于 -型细胞色素，细胞色素 c 和细胞色素 b 的稳态丰度降低，突变体植物的生长受到抑制。观察到复合物 III 的稳态丰度降低可归因于细胞色素 c 是其亚基之一。来自具有细胞色素成熟系统 III 的生物体的可溶性血红素裂解酶的表达可以在功能上弥补 OXA2a 的缺乏。这意味着 OXA2a 是拟南芥系统 I 细胞色素成熟所必需的。由于 OXA2a 在酵母分裂泛素基础相互作用测定中与细胞色素成熟蛋白 CcmF C 末端样蛋白（CCMF）相互作用，我们提出 OXA2a 有助于 CCMF 的膜插入，CCMF 被认为是细胞色素成熟途径的血红素裂解酶组成部分。与 OXA2b 的 TPR 结构域所起的关键作用形成对比，OXA2a 的 TPR 结构域对于其功能不是必需的。
