bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2022‒07‒10
two papers selected by
Gavin McStay
Staffordshire University

  1. J Biol Chem. 2022 Jun 29. pii: S0021-9258(22)00656-1. [Epub ahead of print] 102214
      Mitochondrial translation is a highly regulated process, and newly synthesized mitochondrial products must first associate with several nuclear-encoded auxiliary factors to form oxidative phosphorylation complexes. The output of mitochondrial products should therefore be in stoichiometric equilibrium with the nuclear-encoded products to prevent unnecessary energy expense or the accumulation of pro-oxidant assembly modules. In the mtDNA of Saccharomyces cerevisiae, COX1 encodes subunit 1 of the cytochrome c oxidase, and COB the central core of the cytochrome bc1 electron transfer complex; however, factors regulating the expression of these mitochondrial products are not well described. In this study, we identified Mrx9p as a new factor that controls COX1 and COB expression. We isolated MRX9 in a screen for mitochondrial factors that cause poor accumulation of newly synthesized Cox1p and compromised transition to the respiratory metabolism. Northern analyses indicated lower levels of COX1 and COB mature mRNAs accompanied by an accumulation of unprocessed transcripts in the presence of excess Mrx9p. Furthermore, in a strain devoid of mitochondrial introns, MRX9 overexpression did not affect COX1 and COB translation or respiratory adaptation, implying Mrx9p regulates processing of COX1 and COB RNAs. In addition, we found Mrx9p was localized in the mitochondrial inner membrane, facing the matrix, as a portion of it co-sedimented with mitoribosome subunits and its removal or overexpression altered Mss51p sedimentation. Finally, we showed accumulation of newly synthesized Cox1p in the absence of Mrx9p was diminished in cox14 null mutants. Taken together, these data indicate a regulatory role of Mrx9p in COX1 RNA processing.
    Keywords:  Saccharomyces cerevisiae; intron processing; mitochondrial translation
  2. Biochim Biophys Acta Bioenerg. 2022 Jun 30. pii: S0005-2728(22)00056-1. [Epub ahead of print]1863(7): 148587
      Cardiolipin is the signature phospholipid of the mitochondrial inner membrane. It participates in shaping the inner membrane as well as in modulating the activity of many membrane-bound proteins. The acyl chain composition of cardiolipin is finely tuned post-biosynthesis depending on the surrounding phospholipids to produce mature or unsaturated cardiolipin. However, experimental evidence showing that immature and mature cardiolipin are functionally equivalents for mitochondria poses doubts on the relevance of cardiolipin remodeling. In this work, we studied the role of cardiolipin acyl chain composition in mitochondrial bioenergetics, including a detailed bioenergetic profile of yeast mitochondria. Cardiolipin acyl chains were modified by genetic and nutritional manipulation. We found that both the bioenergetic efficiency and osmotic stability of mitochondria are dependent on the unsaturation level of cardiolipin acyl chains. It is proposed that cardiolipin remodeling and, consequently, mature cardiolipins play an important role in mitochondrial inner membrane integrity and functionality.
    Keywords:  Cardiolipin; Linoleic acid; Membrane; Mitochondria; Yeast