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Rcf2 revealed in cryo-EM structures of hypoxic isoforms of mature mitochondrial III-IV supercomplexes

DOI: 10.1073/pnas.1920612117 DOI Help

Authors: Andrew Hartley (Birkbeck College, University of London) , Brigitte Meunier (CNRS, Commissariat à l’Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay) , Nikos Pinotsis (Birkbeck College, University of London) , Amandine Marechal (Birkbeck, University of London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Proceedings Of The National Academy Of Sciences , VOL 117 , PAGES 9329 - 9337

State: Published (Approved)
Published: April 2020
Diamond Proposal Number(s): 14704

Abstract: The organization of the mitochondrial electron transport chain proteins into supercomplexes (SCs) is now undisputed; however, their assembly process, or the role of differential expression isoforms, remain to be determined. In Saccharomyces cerevisiae, cytochrome c oxidase (CIV) forms SCs of varying stoichiometry with cytochrome bc1 (CIII). Recent studies have revealed, in normoxic growth conditions, an interface made exclusively by Cox5A, the only yeast respiratory protein that exists as one of two isoforms depending on oxygen levels. Here we present the cryo-EM structures of the III2-IV1 and III2-IV2 SCs containing the hypoxic isoform Cox5B solved at 3.4 and 2.8 Å, respectively. We show that the change of isoform does not affect SC formation or activity, and that SC stoichiometry is dictated by the level of CIII/CIV biosynthesis. Comparison of the CIV5B- and CIV5A-containing SC structures highlighted few differences, found mainly in the region of Cox5. Additional density was revealed in all SCs, independent of the CIV isoform, in a pocket formed by Cox1, Cox3, Cox12, and Cox13, away from the CIII–CIV interface. In the CIV5B-containing hypoxic SCs, this could be confidently assigned to the hypoxia-induced gene 1 (Hig1) type 2 protein Rcf2. With conserved residues in mammalian Hig1 proteins and Cox3/Cox12/Cox13 orthologs, we propose that Hig1 type 2 proteins are stoichiometric subunits of CIV, at least when within a III-IV SC.

Journal Keywords: bioenergetics; electron transport chain; cytochrome c oxidase; Hig1 proteins; respiratory supercomplexes

Subject Areas: Biology and Bio-materials

Diamond Offline Facilities: Electron Bio-Imaging Centre (eBIC)
Instruments: Krios III-Titan Krios III at Diamond , Krios IV-Titan Krios IV at Diamond

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