bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2022‒01‒23
eight papers selected by
Gavin McStay
Staffordshire University

  1. Front Mol Biosci. 2021 ;8 798353
      Complex I (CI) is the largest protein complex in the mitochondrial oxidative phosphorylation electron transport chain of the inner mitochondrial membrane and plays a key role in the transport of electrons from reduced substrates to molecular oxygen. CI is composed of 14 core subunits that are conserved across species and an increasing number of accessory subunits from bacteria to mammals. The fact that adding accessory subunits incurs costs of protein production and import suggests that these subunits play important physiological roles. Accordingly, knockout studies have demonstrated that accessory subunits are essential for CI assembly and function. Furthermore, clinical studies have shown that amino acid substitutions in accessory subunits lead to several debilitating and fatal CI deficiencies. Nevertheless, the specific roles of CI's accessory subunits have remained mysterious. In this review, we explore the possible roles of each of mammalian CI's 31 accessory subunits by integrating recent high-resolution CI structures with knockout, assembly, and clinical studies. Thus, we develop a framework of experimentally testable hypotheses for the function of the accessory subunits. We believe that this framework will provide inroads towards the complete understanding of mitochondrial CI physiology and help to develop strategies for the treatment of CI deficiencies.
    Keywords:  accessory subunits; electron transport chain; mitochondrial complex I; mitochondrial diseases; oxidative phosphorylation (OXPHOS)
  2. Proc Natl Acad Sci U S A. 2022 Jan 18. pii: e2114710118. [Epub ahead of print]119(3):
      Mitochondrial ribosomes (mitoribosomes) play a central role in synthesizing mitochondrial inner membrane proteins responsible for oxidative phosphorylation. Although mitoribosomes from different organisms exhibit considerable structural variations, recent insights into mitoribosome assembly suggest that mitoribosome maturation follows common principles and involves a number of conserved assembly factors. To investigate the steps involved in the assembly of the mitoribosomal small subunit (mt-SSU) we determined the cryoelectron microscopy structures of middle and late assembly intermediates of the Trypanosoma brucei mitochondrial small subunit (mt-SSU) at 3.6- and 3.7-Å resolution, respectively. We identified five additional assembly factors that together with the mitochondrial initiation factor 2 (mt-IF-2) specifically interact with functionally important regions of the rRNA, including the decoding center, thereby preventing premature mRNA or large subunit binding. Structural comparison of assembly intermediates with mature mt-SSU combined with RNAi experiments suggests a noncanonical role of mt-IF-2 and a stepwise assembly process, where modular exchange of ribosomal proteins and assembly factors together with mt-IF-2 ensure proper 9S rRNA folding and protein maturation during the final steps of assembly.
    Keywords:  mitochondria; ribosome assembly; structural biology; translation
  3. Semin Cell Dev Biol. 2022 Jan 18. pii: S1084-9521(22)00004-0. [Epub ahead of print]
      The biogenesis of mitochondria requires the coordinated expression of the nuclear and the mitochondrial genomes. However, the vast majority of gene products within the organelle are encoded in the nucleus, synthesized in the cytosol, and imported into mitochondria via the protein import machinery, which permit the entry of proteins to expand the mitochondrial network. Once inside, proteins undergo a maturation and folding process brought about by enzymes comprising the unfolded protein response (UPRmt). Protein import and UPRmt activity must be synchronized and matched with mtDNA-encoded subunit synthesis for proper assembly of electron transport chain complexes to avoid proteotoxicity. This review discusses the functions of the import and UPRmt systems in mammalian skeletal muscle, as well as how exercise alters the equilibrium of these pathways in a time-dependent manner, leading to a new steady state of mitochondrial content resulting in enhanced oxidative capacity and improved muscle health.
    Keywords:  Adaptation; Exercise; Mitochondrial biogenesis; Protein folding; Protein import machinery; Proteostasis
  4. Biomolecules. 2022 Jan 13. pii: 125. [Epub ahead of print]12(1):
      Copper is essential for the stability and activity of cytochrome c oxidase (CcO), the terminal enzyme of the mitochondrial respiratory chain. Copper is bound to COX1 and COX2, two core subunits of CcO, forming the CuB and CuA sites, respectively. Biogenesis of these two copper sites of CcO occurs separately and requires a number of evolutionarily conserved proteins that form the mitochondrial copper delivery pathway. Pathogenic mutations in some of the proteins of the copper delivery pathway, such as SCO1, SCO2, and COA6, have been shown to cause fatal infantile human disorders, highlighting the biomedical significance of understanding copper delivery mechanisms to CcO. While two decades of studies have provided a clearer picture regarding the biochemical roles of SCO1 and SCO2 proteins, some discrepancy exists regarding the function of COA6, the new member of this pathway. Initial genetic and biochemical studies have linked COA6 with copper delivery to COX2 and follow-up structural and functional studies have shown that it is specifically required for the biogenesis of the CuA site by acting as a disulfide reductase of SCO and COX2 proteins. Its role as a copper metallochaperone has also been proposed. Here, we critically review the recent literature regarding the molecular function of COA6 in CuA biogenesis.
    Keywords:  COA6; COX2; CuA site; copper; cytochrome c oxidase; disulfide reductase; metallochaperone; mitochondria
  5. Methods Mol Biol. 2022 ;2413 55-62
      Mitochondrial metabolism plays key roles in pathologies such as cancer. The five complexes of the oxidative phosphorylation (OXPHOS) system are crucial for producing ATP and maintaining cellular functions and are particularly exploited in cancer cells. Understanding the oligomeric state of these OXPHOS complexes will help elucidate their function (or dysfunction) in cancer cells and can be used as a mechanistic tool for anticancer agents that target mitochondria. Here we describe a protocol to observe the oligomeric state of the five OXPHOS complexes by isolating mitochondrial-enriched fractions followed by assessing their oligomeric state by nondenaturing blue native page electrophoresis.
    Keywords:  Mitochondria; Native page; OXPHOS complexes; Oxidative phosphorylation
  6. Int J Mol Sci. 2022 Jan 08. pii: 684. [Epub ahead of print]23(2):
      The last steps of respiration, a core energy-harvesting process, are carried out by a chain of multi-subunit complexes in the inner mitochondrial membrane. Several essential subunits of the respiratory complexes are RNA-edited in plants, frequently leading to changes in the encoded amino acids. While the impact of RNA editing is clear at the sequence and phenotypic levels, the underlying biochemical explanations for these effects have remained obscure. Here, we used the structures of plant respiratory complex I, complex III2 and complex IV to analyze the impact of the amino acid changes of RNA editing in terms of their location and biochemical features. Through specific examples, we demonstrate how the structural information can explain the phenotypes of RNA-editing mutants. This work shows how the structural perspective can bridge the gap between sequence and phenotype and provides a framework for the continued analysis of RNA-editing mutants in plant mitochondria and, by extension, in chloroplasts.
    Keywords:  RNA editing; plant mitochondria; plant respiration; structure-function
  7. Int J Obes (Lond). 2022 Jan 20.
      BACKGROUND: Long non-coding RNAs (lncRNAs) have emerged as a rapidly expanding area of interest in chronic diseases. They are mostly unknown for roles in metabolic regulation. Sirtuins, an epigenetic modulator class, regulate metabolic pathways. However, how sirtuins are regulated via lncRNA is unknown. We hypothesized that a high-fat high-fructose diet (HFD-HF) during pregnancy would increase the risk for obesity via lncRNA-Sirtuin pathways.METHODS: Female C57Bl/6 mice (F0) were fed either chow diet (CD) or HFD-HF for 6 weeks till birth. The pups (F1) were fed either CD or HFD-HF for 20 weeks. Expression of Dleu2, sirtuins, mitochondrial respiratory complexes, and oxidative stress were investigated in the F1 livers. Fasting blood glucose, insulin sensitivity, glucose tolerance, body and tissues weight were measured. A mechanistic interaction was then carried out using a DLEU2 knockdown experiment in the HepG2 cell.
    RESULTS: Dleu2 and sirtuins were both significantly decreased in the livers of HFD-HF fed male F1 whose mothers were either fed CD or HFD-HF during reproductive and pregnancy windows. Confirming this connection, upon silencing DLEU2, transcription levels of SIRT1 through 6 and translational levels of SIRT1, 3, 5, and 6 were significantly downregulated. Knockdown of DLEU2 significantly decreased the protein level of cytochrome-c oxidase (complex IV, MTCO1) without altering other mitochondrial complexes, decreased mitochondrial membrane potential, decreased ATP, and increased reactive oxygen species. Interestingly, in F1 livers, the protein level of MTCO1 was also significantly decreased under an HFD-HF diet or even under chow diet if the mother was exposed to HFD-HF.
    CONCLUSION: Our findings reveal for the first time that one lncRNA can regulate sirtuins and a specific mitochondrial complex. Furthermore, diet or maternal diet can modulate Dleu2 and its downstream regulators in offspring, suggesting a potential role of DLEU2 in metabolic disorders over one or more generations.
  8. Biomedicines. 2021 Dec 28. pii: 60. [Epub ahead of print]10(1):
      Oxidative phosphorylation (OXPHOS) consists of four enzyme complexes and ATP synthase, and is crucial for maintaining physiological tissue and cell growth by supporting the main bioenergy pool. Cytochrome c oxidase (COX) has been implicated as a primary regulatory site of OXPHOS. Recently, COX subunit 5B (COX5B) emerged as a potential biomarker associated with unfavorable prognosis by modulating cell behaviors in specific cancer types. However, its molecular mechanism remains unclear, particularly in colorectal cancers (CRCs). To understand the role of COX5B in CRCs, the expression and postoperative outcome associations using independent in-house patient cohorts were evaluated. A higher COX5B tumor/nontumor expression ratio was associated with unfavorable clinical outcomes (p = 0.001 and 0.011 for overall and disease-free survival, respectively. In cell-based experiments, the silencing of COX5B repressed cell growth and enhanced the susceptibility of CRCs cells to anticancer drugs. Finally, downstream effectors identified by RNA sequencing followed by RT-qPCR and functional compensation experiments revealed that the tight junction protein Claudin-2 (CLDN2) acts downstream of COX5B-mediated bioenergetic alterations in controlling cell growth and the sensitivity to anticancer drugs in CRCs cells. In conclusion, it was found that COX5B promoted cell growth and attenuated anticancer drugs susceptibility in CRCs cells by orchestrating CLDN2 expression, which may contribute to unfavorable postoperative outcomes of patients with CRCs.
    Keywords:  Claudin-2; bioenergetic alteration; colorectal cancers; cytochrome c oxidase subunit 5b; glycolysis; mitochondria; oxidative phosphorylation