Instituto de Investigación Hospital 12 de Octubre (i+12), 28041 Madrid, Spain.
Department of Neurology, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
Cell Rep. 2018 Nov 13;25(7):1786-1799.e4. doi: 10.1016/j.celrep.2018.10.058.
The mitochondrial respiratory chain is organized in a dynamic set of supercomplexes (SCs). The COX7A2L protein is essential for mammalian SC III+IV assembly. However, its function in respirasome (SCs I+III+IV) biogenesis remains controversial. To unambiguously determine the COX7A2L role, we generated COX7A2L-knockout (COX7A2L-KO) HEK293T and U87 cells. COX7A2L-KO cells lack SC III+IV but have enhanced complex III steady-state levels, activity, and assembly rate, normal de novo complex IV biogenesis, and delayed respirasome formation. Nonetheless, the KOs have normal respirasome steady-state levels, and only larger structures (SCs I+III+IV or megacomplexes) were undetected. Functional substrate-driven competition assays showed normal mitochondrial respiration in COX7A2L-KO cells in standard and nutritional-, environmental-, and oxidative-stress-challenging conditions. We conclude that COX7A2L establishes a regulatory checkpoint for the biogenesis of CIII and specific SCs, but the COX7A2L-dependent MRC remodeling is essential neither to maintain mitochondrial bioenergetics nor to cope with acute cellular stresses.
线粒体呼吸链组织在一组动态的超级复合物（SCs）中。COX7A2L 蛋白对于哺乳动物 SC III+IV 的组装是必不可少的。然而，其在呼吸体（SCs I+III+IV）生物发生中的功能仍存在争议。为了明确 COX7A2L 的作用，我们生成了 COX7A2L 敲除（COX7A2L-KO）HEK293T 和 U87 细胞。COX7A2L-KO 细胞缺乏 SC III+IV，但具有增强的复合物 III 稳态水平、活性和组装速率、正常的从头复合物 IV 生物发生以及延迟的呼吸体形成。尽管如此，KO 细胞具有正常的呼吸体稳态水平，只有更大的结构（SCs I+III+IV 或巨型复合物）未被检测到。功能性底物驱动的竞争测定显示 COX7A2L-KO 细胞在标准和营养、环境和氧化应激挑战条件下的线粒体呼吸正常。我们得出结论，COX7A2L 为 CIII 和特定 SCs 的生物发生建立了一个调节检查点，但 COX7A2L 依赖性 MRC 重塑对于维持线粒体生物能量学或应对急性细胞应激既不是必需的。
