bims-resufa Biomed News
on Respiratory supercomplex factors
Issue of 2019‒10‒13
two papers selected by
Vera Strogolova
Strong Microbials, Inc

  1. J Biol Chem. 2019 Oct 07. pii: jbc.RA119.010317. [Epub ahead of print]
    Hoang NH, Strogolova V, Mosley JJ, Stuart RA, Hosler J.
      Hypoxia-inducible gene domain 1 (HIGD1) proteins are small integral membrane proteins, conserved from bacteria to humans, that associate with oxidative phosphorylation supercomplexes. Using yeast as a model organism, we have previously shown that its two HIGD1 proteins, Rcf1 and Rcf2, are required for the generation and maintenance of a normal membrane potential (Δψ) across the inner mitochondrial membrane (IMM). We have postulated that the lower Δψ observed in the absence of the HIGD1 proteins may be due to decreased proton pumping by complex IV (CIV) or to an enhanced leakage of protons across the IMM. Here, we measured the Δψ generated by complex III (CIII) to discriminate between these possibilities. First, we found that the decreased Δψ observed in the absence of the HIGD1 proteins cannot be due to decreased proton pumping by CIV, since CIII, operating alone, also exhibited a decreased Δψ when HIGD1 proteins were absent. Since CIII can neither lower its pumping stoichiometry nor transfer protons completely across the IMM, this result indicates that HIGD1 protein ablation enhances proton leakage across the IMM. Second, we demonstrate that this proton leakage occurs through CIV, since Δψ generation by CIII is restored when CIV is removed from the cell. Third, the proton leakage appeared to take place through an inactive population of CIV that accumulates when HIGD1 proteins are absent. We conclude that HIGD1 proteins in yeast prevent CIV inactivation, likely by preventing the loss of lipids bound within the Cox3 protein of CIV.
    Keywords:  Rcf; cytochrome c oxidase (Complex IV); hypoxia-inducible gene domain 1 (HIGD1); lipid-protein interaction; mitochondria; mitochondrial membrane potential; oxidative phosphorylation; proton leak; respiration; suicide inactivation
  2. FEBS J. 2019 Oct 09.
    Wolf A, Wonneberg J, Balke J, Alexiev U.
      Cytochrome c oxidase (CcO), the terminal enzyme of the respiratory chain of mitochondria and many aerobic prokaryotes that functions as a redox-coupled proton pump, catalyzes the reduction of molecular oxygen to water. As part of the respiratory chain, CcO contributes to the proton motive force driving ATP synthesis. While many aspects of the enzyme's catalytic mechanisms have been established, a clear picture of the proton exit pathway(s) remains elusive. Here, we aim to gain insight into the molecular mechanisms of CcO through the development of a new homologous mutagenesis/expression system in Paracoccus denitrificans, which allows mutagenesis of CcO subunits 1, 2, and 3. Our system provides true single thiol-reactive CcO variants in a three-subunit base variant with unique labeling sites for the covalent attachment of reporter groups sensitive to nanoenvironmental factors like protonation, polarity, and hydration. To this end, we exchanged six residues on both membrane sides of CcO for cysteines. We show redox-dependent wetting changes at the proton uptake channel and increased polarity at the proton exit side of CcO upon electronation. We suggest an electronation dependent conformational change to play a role in proton exit from CcO.
    Keywords:  Cytochrome c oxidase; conformational change; fluorescence spectroscopy; hydration; site-directed fluorescence labeling