bims-resufa Biomed News
on Respiratory supercomplex factors
Issue of 2019‒12‒15
three papers selected by
Vera Strogolova
Strong Microbials, Inc

  1. Biochim Biophys Acta Bioenerg. 2019 Dec 08. pii: S0005-2728(19)30191-4. [Epub ahead of print] 148137
    Szibor M, Gainutdinov T, Fernandez-Vizarra E, Dufour E, Gizatullina Z, Debska-Vielhaber G, Heidler J, Wittig I, Viscomi C, Gellerich F, Moore AL.
      Electron transfer from all respiratory chain dehydrogenases of the electron transport chain (ETC) converges at the level of the quinone (Q) pool. The Q redox state is thus a function of electron input (reduction) and output (oxidation) and closely reflects the mitochondrial respiratory state. Disruption of electron flux at the level of the cytochrome bc1 complex (cIII) or cytochrome c oxidase (cIV) shifts the Q redox poise to a more reduced state which is generally sensed as respiratory stress. To cope with respiratory stress, many species, but not insects and vertebrates, express alternative oxidase (AOX) which acts as an electron sink for reduced Q and by-passes cIII and cIV. Here, we used Ciona intestinalis AOX xenotopically expressed in mouse mitochondria to study how respiratory states impact the Q poise and how AOX may be used to restore respiration. Particularly interesting is our finding that electron input through succinate dehydrogenase (cII), but not NADH:ubiquinone oxidoreductase (cI), reduces the Q pool almost entirely (>90%) irrespective of the respiratory state. AOX enhances the forward electron transport (FET) from cII thereby decreasing reverse electron transport (RET) and ROS specifically when non-phosphorylating. AOX is not engaged with cI substrates, however, unless a respiratory inhibitor is added. This sheds new light on Q poise signaling, the biological role of cII which enigmatically is the only ETC complex absent from respiratory supercomplexes but yet participates in the tricarboxylic acid (TCA) cycle. Finally, we delineate potential risks and benefits arising from therapeutic AOX transfer.
    Keywords:  Alternative oxidase (AOX); Mitochondria; OXPHOS; Quinone pool; ROS; Xenotopic expression
  2. Biochim Biophys Acta Bioenerg. 2019 Dec 08. pii: S0005-2728(19)30187-2. [Epub ahead of print] 148133
    Tropeano CV, Aleo SJ, Zanna C, Roberti M, Scandiffio L, Polosa PL, Fiori J, Porru E, Roda A, Carelli V, Steimle S, Daldal F, Rugolo M, Ghelli A.
      The respiratory complexes are organized in supramolecular assemblies called supercomplexes thought to optimize cellular metabolism under physiological and pathological conditions. In this study, we used genetically and biochemically well characterized cells bearing the pathogenic microdeletion m.15,649-15,666 (ΔI300-P305) in MT-CYB gene, to investigate the effects of an assembly-hampered CIII on the re-organization of supercomplexes. First, we found that this mutation also affects the stability of both CI and CIV, and evidences the occurrence of a preferential structural interaction between CI and CIII2, yielding a small amount of active CI + CIII2 supercomplex. Indeed, a residual CI + CIII combined redox activity, and a low but detectable ATP synthesis driven by CI substrates are detectable, suggesting that the assembly of CIII into the CI + CIII2 supercomplex mitigates the detrimental effects of MT-CYB deletion. Second, measurements of oxygen consumption and ATP synthesis driven by NADH-linked and FADH2-linked substrates alone, or in combination, indicate a common ubiquinone pool for the two respiratory pathways. Finally, we report that prolonged incubation with rotenone enhances the amount of CI and CIII2, but reduces CIV assembly. Conversely, the antioxidant N-acetylcysteine increases CIII2 and CIV2 and partially restores respirasome formation. Accordingly, after NAC treatment, the rate of ATP synthesis increases by two-fold compared with untreated cell, while the succinate level, which is enhanced by the homoplasmic mutation, markedly decreases. Overall, our findings show that fine-tuning the supercomplexes stability improves the energetic efficiency of cells with the MT-CYB microdeletion.
    Keywords:  Cytochrome b depletion complex III dysfunction; MT-CYB gene in-frame microdeletion; N-acetylcysteine, rotenone; Respiratory chain supercomplexes
  3. Anal Biochem. 2019 Dec 05. pii: S0003-2697(19)31019-X. [Epub ahead of print]590 113515
    L P, D K, J K, Cl H, N L.
      Bioenergetic function is characterized with assays obtained by polarographic systems. Analog systems without data acquisition, visualization, and processing tools are used but require cumbersome operations to derive respiration rate and ADP to oxygen stoichiometry of oxidative phosphorylation (ADP/O ratio). The analog signal of a polarograhic system (YSI-5300) was digitized and a graphical user interface (GUI) was developed in MATLAB to integrate visualization, recording, calibration and processing of bioenergetic data. With the GUI, the signal is continuously visualized during the experiment and respiratory rates and ADP/O ratios can be determined. The integrated system was tested to evaluate bioenergetic function of subpopulations of mitochondria isolated from rat skeletal muscle (n = 10). Signal processing was applied to denoise data recorded at the sampling rate of 1000Hz, and maximize data decimation for computational applications. The error in calculating the bioenergetic outputs using decimated data is negligible when data are denoised. The estimate of respiration rate, ADP/O ratio and RCR obtained with denoised data at sampling rate as low as 5Hz was similar to that obtained with raw data recorded at sampling rate of 1000Hz. In summary, the integrated tools of the GUI overcome the limitations of data processing, accuracy, and utilization of analog polarographic systems.
    Keywords:  ADP/O ratio; Computational methods; Kinetics; Mitochondria; Respiration rate; Software