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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 115; no. 12; pp. 3024 - 3029
• Main Authors: Davies, Karen M, Blum, Thorsten B, Kühlbrandt, Werner
• Format: Journal Article
• Language: English
• Published: United States 20-03-2018
• Subjects: subtomogram averaging; respirasomes; cryo-electron tomography; mitochondria; respiratory chain supercomplexes
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1720702115

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
was essentially conserved in all supercomplexes investigated. In addition, up to two copies of monomeric complex IV were associated with the complex I
III
assembly in bovine heart and the yeast
, but their positions varied. No complex IV was detected in the respiratory supercomplex of the plant
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
, but otherwise their stoichiometry and structure varies. The conserved features of supercomplex assemblies indicate an important role in respiratory electron transfer.