Conserved in situ arrangement of complex I and III 2 in mitochondrial respiratory chain supercomplexes of mammals, yeast, and plants.

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 III ₂ was essentially conserved in all supercomplexes investigated. In addition, up to two copies of monomeric complex IV were associated with the complex I ₁ III ₂ 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 III ₂ , but otherwise their stoichiometry and structure varies. The conserved features of supercomplex assemblies indicate an important role in respiratory electron transfer.
Competing Interests: The authors declare no conflict of interest.
(Copyright © 2018 the Author(s). Published by PNAS.)