bims-resufa 2020-06-07 papers

Issue of 2020–06–07
three papers selected by
Vera Strogolova, Marquette University

Front Plant Sci. 2020 ;11 566

Roles for Plant Mitochondrial Alternative Oxidase Under Normoxia, Hypoxia, and Reoxygenation Conditions.

Jayamini Jayawardhane, Devin W Cochrane, Poorva Vyas, Natalia V Bykova, Greg C Vanlerberghe, Abir U Igamberdiev.

Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain (ETC) that has a lower affinity for oxygen than does cytochrome (cyt) oxidase. To investigate the role(s) of AOX under different oxygen conditions, wild-type (WT) Nicotiana tabacum plants were compared with AOX knockdown and overexpression plants under normoxia, hypoxia (near-anoxia), and during a reoxygenation period following hypoxia. Paradoxically, under all the conditions tested, the AOX amount across plant lines correlated positively with leaf energy status (ATP/ADP ratio). Under normoxia, AOX was important to maintain respiratory carbon flow, to prevent the mitochondrial generation of superoxide and nitric oxide (NO), to control lipid peroxidation and protein S-nitrosylation, and possibly to reduce the inhibition of cyt oxidase by NO. Under hypoxia, AOX was again important in preventing superoxide generation and lipid peroxidation, but now contributed positively to NO amount. This may indicate an ability of AOX to generate NO under hypoxia, similar to the nitrite reductase activity of cyt oxidase under hypoxia. Alternatively, it may indicate that AOX activity simply reduces the amount of superoxide scavenging of NO, by reducing the availability of superoxide. The amount of inactivation of mitochondrial aconitase during hypoxia was also dependent upon AOX amount, perhaps through its effects on NO amount, and this influenced carbon flow under hypoxia. Finally, AOX was particularly important in preventing nitro-oxidative stress during the reoxygenation period, thereby contributing positively to the recovery of energy status following hypoxia. Overall, the results suggest that AOX plays a beneficial role in low oxygen metabolism, despite its lower affinity for oxygen than cytochrome oxidase.

Keywords: alternative oxidase; hypoxia; mitochondria; nitric oxide; reactive oxygen species; reoxygenation

DOI: https://doi.org/10.3389/fpls.2020.00566

EMBO Rep. 2020 Jun 04. e50287

Scaf1 promotes respiratory supercomplexes and metabolic efficiency in zebrafish.

Carolina García-Poyatos, Sara Cogliati, Enrique Calvo, Pablo Hernansanz-Agustín, Sylviane Lagarrigue, Ricardo Magni, Marius Botos, Xavier Langa, Francesca Amati, Jesús Vázquez, Nadia Mercader, José Antonio Enríquez.

The oxidative phosphorylation (OXPHOS) system is a dynamic system in which the respiratory complexes coexist with super-assembled quaternary structures called supercomplexes (SCs). The physiological role of SCs is still disputed. Here, we used zebrafish to study the relevance of respiratory SCs. We combined immunodetection analysis and deep data-independent proteomics to characterize these structures and found similar SCs to those described in mice, as well as novel SCs including III2 + IV2 , I + IV, and I + III2 + IV2 . To study the physiological role of SCs, we generated two null allele zebrafish lines for supercomplex assembly factor 1 (scaf1). scaf1-/- fish displayed altered OXPHOS activity due to the disrupted interaction of complexes III and IV. scaf1-/- fish were smaller in size and showed abnormal fat deposition and decreased female fertility. These physiological phenotypes were rescued by doubling the food supply, which correlated with improved bioenergetics and alterations in the metabolic gene expression program. These results reveal that SC assembly by Scaf1 modulates OXPHOS efficiency and allows the optimization of metabolic resources.

Keywords: OXPHOS super-assembly; SCAF1/COX7A2L; metabolism; mitochondria; zebrafish

DOI: https://doi.org/10.15252/embr.202050287

Biochim Biophys Acta Bioenerg. 2020 May 30. pii: S0005-2728(20)30087-6. [Epub ahead of print] 148237

Modulation of the electron-proton coupling at cytochrome a by the ligation of the oxidized catalytic center in bovine cytochrome c oxidase.

Katarina Kopcova, Ludmila Mikulova, Ivana Pechova, Tereza Sztachova, Erik Cizmar, Daniel Jancura, Marian Fabian.

Cytochrome a was suggested as the key redox center in the proton pumping process of bovine cytochrome c oxidase (CcO). Recent studies showed that both the structure of heme a and its immediate vicinity are sensitive to the ligation and the redox state of the distant catalytic center composed of iron of cytochrome a3 (Fea3) and copper (CuB). Here, the influence of the ligation at the oxidized Fea33+- CuB2+ center on the electron-proton coupling at heme a was examined in the wide pH range (6.5-11). The strength of the coupling was evaluated by the determination of pH dependence of the midpoint potential of heme a (Em(a)) for the cyanide (the low spin Fea33+) and the formate-ligated CcO (the high spin Fea33+). The measurements were performed under experimental conditions when other three redox centers of CcO are oxidized. Two slightly differing linear pH dependencies of Em(a) were found for the CN- and the formate-ligated CcO with slopes of -13 mV/pH unit and -23 mV/pH unit, respectively. These linear dependencies indicate only a weak and unspecific electron-proton coupling at cytochrome a in both forms of CcO. The lack of the strong electron-proton coupling at the physiological pH values is also substantiated by the UV-Vis absorption and electron-paramagnetic resonance spectroscopy investigations of the cyanide-ligated oxidized CcO. It is shown that the ligand exchange at Fea3+ between His-Fea3+-His and His-Fea3+-OH occurs only at pH above 9.5 with the estimated pK >11.0.

Keywords: Cytochrome a; Cytochrome c; Cytochrome c oxidase; Electron - paramagnetic resonance spectroscopy; Redox potential; pH dependence

DOI: https://doi.org/10.1016/j.bbabio.2020.148237