We used electron cryo-tomography and subtomogram averaging to investigate the structure of complex I and its supramolecular assemblies in the inner mitochondrial membrane of mammals, fungi, and plants. Tomographic volumes containing complex I were averaged at ∼4 nm resolution. Principal component analysis indicated that ∼60% of complex I formed a supercomplex with dimeric complex III, while ∼40% were not associated with other respiratory chain complexes. The mutual arrangement of complex I and III₂ was essentially conserved in all supercomplexes investigated. In addition, up to two copies of monomeric complex IV were associated with the complex I₁III₂ assembly in bovine heart and the yeast Yarrowia lipolytica, but their positions varied. No complex IV was detected in the respiratory supercomplex of the plant Asparagus officinalis. Instead, an ∼4.5-nm globular protein density was observed on the matrix side of the complex I membrane arm, which we assign to γ-carbonic anhydrase. Our results demonstrate that respiratory chain supercomplexes in situ have a conserved core of complex I and III₂, but otherwise their stoichiometry and structure varies. The conserved features of supercomplex assemblies indicate an important role in respiratory electron transfer.

我们使用电子冷冻断层摄影术和亚断层摄影术平均研究了哺乳动物，真菌和植物的线粒体内膜中复合物I及其超分子组装体的结构。包含复合物I的层析成像体积的平均分辨率约为4 nm。主成分分析表明，约60％的复合物I与二聚体复合物III形成超复合物，而约40％的复合物与其他呼吸链复合物无关。复合物I和III ₂的相互排列在所有研究的超级复合物中基本上都得到保留。另外，在牛心和酵母解脂耶氏酵母中，最多有两个拷贝的单体复合物IV与复合物I ₁ III ₂组装相​​关。，但他们的立场各不相同。在芦笋的呼吸超复合物中没有检测到复合物IV 。相反，在复杂的I膜臂的基质侧观察到了约4.5 nm的球状蛋白密度，我们将其分配为γ-碳酸酐酶。我们的结果表明，原位呼吸链超复合物具有复合物I和III ₂的保守核，但其他方面其化学计量和结构也有所不同。超复杂组件的保守特征表明在呼吸电子转移中起重要作用。