In yeast (Saccharomyces cerevisiae) and human (Homo sapiens) mitochondria, Oxidase assembly protein1 (Oxa1) is the general insertase for protein insertion from the matrix side into the inner membrane while Cytochrome c oxidase assembly protein18 (Cox18/Oxa2) is specifically involved in the topogenesis of the complex IV subunit, Cox2. Arabidopsis (Arabidopsis thaliana) 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 OXA2a transfer-DNA insertional mutants using the developmentally regulated ABSCISIC ACID INSENSITIVE3 (ABI3) promoter. The ABI3p:OXA2a plants displayed growth retardation due to a reduction in the steady-state abundances of both c-type cytochromes, cytochrome c₁ and cytochrome c. The observed reduction in the steady-state abundance of complex III could be attributed to cytochrome c₁ being one of its subunits. Expression of a soluble heme lyase from an organism with cytochrome c maturation system III could functionally complement the lack of OXA2a. This implies that OXA2a is required for the system I cytochrome c maturation of Arabidopsis. Due to the interaction of OXA2a with Cytochrome c maturation protein CcmF C-terminal-like protein (CCMF_C) in a yeast split-ubiquitin based interaction assay, we propose that OXA2a aids in the membrane insertion of CCMF_C, which is presumed to form the heme lyase component of the cytochrome c 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（酿酒酵母）和人类（智人）线粒体中，氧化酶组装蛋白 1 (Oxa1) 是蛋白质从基质侧插入内膜的通用插入酶，而细胞色素c氧化酶组装蛋白 18 (Cox18/Oxa2) 专门参与复杂 IV 亚基 Cox2 的拓扑发生。拟南芥 ( Arabidopsis thaliana ) 线粒体含有四种 OXA 同源物：OXA1a、OXA1b、OXA2a 和 OXA2b。OXA2a 和 OXA2b 是 Oxa1 超家族的独特成员，因为它们的 C 末端具有四肽重复 (TPR) 结构域。在这里，我们通过研究使用发育调控的脱落酸不敏感 3 ( ABI3 ) 启动子部分互补纯合致死OXA2a转移 DNA 插入突变体产生的存活突变体植物来确定 OXA2a 的作用。ABI3p :OXA2a植物由于c型细胞色素、细胞色素c ₁和细胞色素c的稳态丰度降低而表现出生长迟缓。观察到的复合物 III 稳态丰度的减少可归因于细胞色素c ₁是其亚基之一。来自具有细胞色素c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补充 OXA2a 的缺乏。这意味着 OXA2a 是拟南芥系统 I 细胞色素c成熟所必需的。由于 OXA2a 在基于酵母分裂泛素的相互作用测定中与细胞色素c成熟蛋白 CcmF C 末端样蛋白 (CCMF _C ) 的相互作用，我们提出 OXA2a 有助于 CCMF _C的膜插入，推测其形成细胞色素c成熟途径的血红素裂解酶成分。与 OXA2b 的 TPR 结构域发挥的关键作用相反，OXA2a 的 TPR 结构域对其功能而言并不是必需的。