The respiratory megacomplex represents the highest-order assembly of respiratory chain complexes, and it allows mitochondria to respond to energy-requiring conditions. To understand its architecture, we examined the human respiratory chain megacomplex-I₂III₂IV₂ (MCI₂III₂IV₂) with 140 subunits and a subset of associated cofactors using cryo-electron microscopy. The MCI₂III₂IV₂ forms a circular structure with the dimeric CIII located in the center, where it is surrounded by two copies each of CI and CIV. Two cytochrome c (Cyt.c) molecules are positioned to accept electrons on the surface of the c₁ state CIII dimer. Analyses indicate that CII could insert into the gaps between CI and CIV to form a closed ring, which we termed the electron transport chain supercomplex. The structure not only reveals the precise assignment of individual subunits of human CI and CIII, but also enables future in-depth analysis of the electron transport chain as a whole.

中文翻译：

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人线粒体呼吸性大复合体I2III2IV2的体系结构。

呼吸复合体代表了呼吸链复合体的最高阶组装，它使线粒体对能量需求条件做出反应。为了了解其体系结构，我们使用低温电子显微镜检查了具有140个亚基和相关辅助因子子集的人类呼吸链大复合体-I ₂ III ₂ IV ₂（MCI ₂ III ₂ IV ₂）。MCI ₂ III ₂ IV ₂形成圆形结构，二聚体CIII位于中心，在其中被CI和CIV的两个副本包围。放置两个细胞色素c（Cyt.c）分子以接受c表面上的电子_1种状态的CIII二聚体。分析表明，CII可以插入CI和CIV之间的间隙中，形成一个闭环，我们称其为电子传输链超复合物。该结构不仅揭示了人类CI和CIII各个亚基的精确分配，而且使未来对整个电子传输链的深入分析成为可能。