Centre for Reproduction and Development, Monash Institute of Medical Research, Clayton 3168, Australia.
J Mol Biol. 2011 Dec 2;414(3):413-26. doi: 10.1016/j.jmb.2011.10.012. Epub 2011 Oct 14.
The assembly of complex I (NADH-ubiquinone oxidoreductase) is a complicated process, requiring the integration of 45 subunits encoded by both nuclear and mitochondrial DNAs into a structure of approximately 1 MDa. A number of "assembly factors" that aid complex I biogenesis have recently been described, including C8orf38. This protein was identified as an assembly factor by its evolutionary conservation in organisms containing complex I and by a C8orf38 mutation in a patient presenting with Leigh syndrome and isolated complex I deficiency. In this report, we have undertaken the characterization of C8orf38 and its role in complex I assembly. Analysis of mitochondria from fibroblasts of a patient harboring a C8orf38 mutation showed almost undetectable levels of steady-state complex I and defective biogenesis of the mtDNA-encoded subunit ND1. Complementation with wild-type C8orf38 restored the levels of both ND1 and complex I, confirming the C8orf38 mutation as the cause of the complex I defect in the patient. In the absence of ND1 in patient cells, early- and mid-stage intermediate complexes were still formed; however, assembly of late-stage intermediates was impaired, indicating a convergence point in the assembly process. While C8orf38 appears to behave at a step in complex I biogenesis similar to that of the assembly factor C20orf7, complementation studies showed that both proteins are required for ND1 synthesis/stabilization. We conclude that C8orf38 is a crucial factor required for the translation and/or integration of ND1 into an early-stage assembly intermediate and that mutation of C8orf38 disrupts the initial stages of complex I biogenesis.
复杂 I（NADH-泛醌氧化还原酶）的组装是一个复杂的过程，需要将核 DNA 和线粒体 DNA 编码的 45 个亚基整合到一个大约 1MDa 的结构中。最近描述了许多“组装因子”，它们有助于复杂 I 的生物发生，包括 C8orf38。该蛋白被鉴定为组装因子，因为它在含有复杂 I 的生物中具有进化保守性，并且在患有 Leigh 综合征和孤立的复杂 I 缺乏症的患者中存在 C8orf38 突变。在本报告中，我们对 C8orf38 及其在复杂 I 组装中的作用进行了表征。对携带 C8orf38 突变的成纤维细胞中线粒体的分析表明，稳定状态的复杂 I 几乎无法检测到，并且 mtDNA 编码的亚基 ND1 的生物发生缺陷。用野生型 C8orf38 进行互补恢复了 ND1 和复杂 I 的水平，证实了 C8orf38 突变是患者中复杂 I 缺陷的原因。在患者细胞中缺乏 ND1 的情况下，仍然形成了早期和中期中间复合物；然而，晚期中间复合物的组装受到了损害，表明组装过程存在一个收敛点。虽然 C8orf38 似乎在复杂 I 生物发生的一个步骤中表现得类似于组装因子 C20orf7，但互补研究表明，这两种蛋白质都需要 ND1 的合成/稳定。我们得出结论，C8orf38 是将 ND1 翻译和/或整合到早期组装中间复合物中所必需的关键因素，并且 C8orf38 的突变会破坏复杂 I 生物发生的初始阶段。
