bims-resufa 2020-04-19 papers

Issue of 2020–04–19
three papers selected by
Vera Strogolova, Marquette University

Proc Natl Acad Sci U S A. 2020 Apr 14. pii: 201920612. [Epub ahead of print]

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

Andrew M Hartley, Brigitte Meunier, Nikos Pinotsis, Amandine Maréchal.

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 bc 1 (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.

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

DOI: https://doi.org/10.1073/pnas.1920612117

Proc Natl Acad Sci U S A. 2020 Apr 14. pii: 202001572. [Epub ahead of print]

A common coupling mechanism for A-type heme-copper oxidases from bacteria to mitochondria.

Amandine Maréchal, Jing-Yang Xu, Naho Genko, Andrew M Hartley, Francis Haraux, Brigitte Meunier, Peter R Rich.

Mitochondria metabolize almost all the oxygen that we consume, reducing it to water by cytochrome c oxidase (CcO). CcO maximizes energy capture into the protonmotive force by pumping protons across the mitochondrial inner membrane. Forty years after the H+/e- stoichiometry was established, a consensus has yet to be reached on the route taken by pumped protons to traverse CcO's hydrophobic core and on whether bacterial and mitochondrial CcOs operate via the same coupling mechanism. To resolve this, we exploited the unique amenability to mitochondrial DNA mutagenesis of the yeast Saccharomyces cerevisiae to introduce single point mutations in the hydrophilic pathways of CcO to test function. From adenosine diphosphate to oxygen ratio measurements on preparations of intact mitochondria, we definitely established that the D-channel, and not the H-channel, is the proton pump of the yeast mitochondrial enzyme, supporting an identical coupling mechanism in all forms of the enzyme.

Keywords: ADP/O ratio; H/e stoichiometry; cytochrome c oxidase; mitochondria; proton pumping

DOI: https://doi.org/10.1073/pnas.2001572117

Proc Natl Acad Sci U S A. 2020 Apr 17. pii: 201917948. [Epub ahead of print]

Moderation of mitochondrial respiration mitigates metabolic syndrome of aging.

Mojdeh Tavallaie, Ramouna Voshtani, Xinxian Deng, Yixue Qiao, Faqin Jiang, James P Collman, Lei Fu.

Deregulation of mitochondrial dynamics leads to the accumulation of oxidative stress and unhealthy mitochondria; consequently, this accumulation contributes to premature aging and alterations in mitochondria linked to metabolic complications. We postulate that restrained mitochondrial ATP synthesis might alleviate age-associated disorders and extend healthspan in mammals. Herein, we prepared a previously discovered mitochondrial complex IV moderate inhibitor in drinking water and orally administered to standard-diet-fed, wild-type C57BL/6J mice every day for up to 16 mo. No manifestation of any apparent toxicity or deleterious effect on studied mouse models was observed. The impacts of an added inhibitor on a variety of mitochondrial functions were analyzed, such as respiratory activity, mitochondrial bioenergetics, and biogenesis, and a few age-associated comorbidities, including reactive oxygen species (ROS) production, glucose abnormalities, and obesity in mice. It was found that mitochondrial quality, dynamics, and oxidative metabolism were greatly improved, resulting in lean mice with a specific reduction in visceral fat plus superb energy and glucose homeostasis during their aging period compared to the control group. These results strongly suggest that a mild interference in ATP synthesis through moderation of mitochondrial activity could effectively up-regulate mitogenesis, reduce ROS production, and preserve mitochondrial integrity, thereby impeding the onset of metabolic syndrome. We conclude that this inhibitory intervention in mitochondrial respiration rectified the age-related physiological breakdown in mice by protecting mitochondrial function and markedly mitigated certain undesired primary outcomes of metabolic syndrome, such as obesity and type 2 diabetes. This intervention warrants further research on the treatment of metabolic syndrome of aging in humans.

Keywords: aging; cytochrome c oxidase; metabolic syndrome; mitochondria; mitogenesis

DOI: https://doi.org/10.1073/pnas.1917948117