bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2021‒06‒06
twelve papers selected by
Gavin McStay
Staffordshire University

  1. Life (Basel). 2021 May 19. pii: 455. [Epub ahead of print]11(5):
      NADH:ubiquinone-oxidoreductase (complex I) is the largest membrane protein complex of the respiratory chain. Complex I couples electron transfer to vectorial proton translocation across the inner mitochondrial membrane. The L shaped structure of complex I is divided into a membrane arm and a matrix arm. Fourteen central subunits are conserved throughout species, while some 30 accessory subunits are typically found in eukaryotes. Complex I dysfunction is associated with mutations in the nuclear and mitochondrial genome, resulting in a broad spectrum of neuromuscular and neurodegenerative diseases. Accessory subunit NDUFS4 in the matrix arm is a hot spot for mutations causing Leigh or Leigh-like syndrome. In this review, we focus on accessory subunits of the matrix arm and discuss recent reports on the function of accessory subunit NDUFS4 and its interplay with NDUFS6, NDUFA12, and assembly factor NDUFAF2 in complex I assembly.
    Keywords:  Leigh syndrome; NADH dehydrogenase; assembly factor; mitochondrial disease; oxidative phosphorylation; respiratory chain
  2. Front Genet. 2021 ;12 638749
      Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a maternally inherited mitochondrial disease. Most cases of MELAS are caused by the m.3243A > G variant in the MT-TL1 gene encoding tRNALeu(UUR). However, the genetic cause in 10% of patients with MELAS is unknown. We investigated the pathogenicity of the novel mtDNA variant m.9396G > A/MT-CO3 (p.E64K), which affects an extremely conserved amino acid in the CO3 subunit of mitochondrial respiratory chain (MRC) complex IV (CIV) in a patient with MELAS. Biochemical assays of a muscle biopsy confirmed remarkable CIV deficiency, and pathological examination showed ragged red fibers and generalized COX non-reactive muscle fibers. Transfer of the mutant mtDNA into cybrids impaired CIV assembly, followed by remarkable mitochondrial dysfunction and ROS production. Our findings highlight the pathogenicity of a novel m.9396G > A variant and extend the spectrum of pathogenic mtDNA variants.
    Keywords:  MELAS; MT-CO3 gene; complex IV of respiratory chain; mitochondrial diseases; novel mitochondrial DNA variant
  3. Life (Basel). 2021 May 11. pii: 432. [Epub ahead of print]11(5):
      The fact that >99% of mitochondrial proteins are encoded by the nuclear genome and synthesised in the cytosol renders the process of mitochondrial protein import fundamental for normal organelle physiology. In addition to this, the nuclear genome comprises most of the proteins required for respiratory complex assembly and function. This means that without fully functional protein import, mitochondrial respiration will be defective, and the major cellular ATP source depleted. When mitochondrial protein import is impaired, a number of stress response pathways are activated in order to overcome the dysfunction and restore mitochondrial and cellular proteostasis. However, prolonged impaired mitochondrial protein import and subsequent defective respiratory chain function contributes to a number of diseases including primary mitochondrial diseases and neurodegeneration. This review focuses on how the processes of mitochondrial protein translocation and respiratory complex assembly and function are interlinked, how they are regulated, and their importance in health and disease.
    Keywords:  mitochondrial dysfunction; mitochondrial proteostasis; neurodegeneration; protein import; respiratory complex assembly; supercomplexes
  4. Mol Biol Rep. 2021 Jun 05.
      Mitochondrial diseases include a wide group of clinically heterogeneous disorders caused by a dysfunction of the mitochondrial respiratory chain and can be related to mutations in nuclear or mitochondrial DNA genes. In the present report, we performed a whole mitochondrial genome screening in two patients with clinical features of mitochondrial diseases. Mutational analysis revealed the presence of two undescribed heteroplasmic mitochondrial variations, the m.3911A > G (E202G) variant in the MT-ND1 gene found in two patients (P1 and P2) and the m.12058A > C (E433D) pathogenic variant in the MT-ND4 gene present only in patient P2 who had a more severe phenotype. These two substitutions were predicted to be damaging by several bioinformatics tools and lead to amino acid changes in two conserved residues localized in two important functional domains of the mitochondrial subunits of complex I. Furthermore, the 3D modeling suggested that the two amino acid changes could therefore alter the structure of the two subunits and may decrease the stability and the function of complex I. The two described pathogenic variants found in patient P2 could act synergically and alter the complex I function by affecting the proton pumping processes and the energy production and then could explain the severe phenotype compared to patient P1 presenting only the E202G substitution in ND1.
    Keywords:  MT-ND1; MT-ND4; Mitochondrial diseases; m.12058A > C; m.3911A > G; mtDNA
  5. Cells. 2021 May 11. pii: 1164. [Epub ahead of print]10(5):
      The central role mitochondria play in cellular homeostasis has made its study critical to our understanding of various aspects of human health and disease. Mitochondria rely on the translocase of the outer membrane (TOM) complex for the bulk of mitochondrial protein import. In addition to its role as the major entry point for mitochondrial proteins, the TOM complex serves as an entry pathway for viral proteins. TOM complex subunits also participate in a host of interactions that have been studied extensively for their function in neurodegenerative diseases, cardiovascular diseases, innate immunity, cancer, metabolism, mitophagy and autophagy. Recent advances in our structural understanding of the TOM complex and the protein import machinery of the outer mitochondrial membrane have made structure-based therapeutics targeting outer mitochondrial membrane proteins during mitochondrial dysfunction an exciting prospect. Here, we describe advances in understanding the TOM complex, the interactome of the TOM complex subunits, the implications for the development of therapeutics, and our understanding of the structure/function relationship between components of the TOM complex and mitochondrial homeostasis.
    Keywords:  TOM complex; TOM complex interactions; TOM subunits; mitochondrial cell signaling; mitochondrial quality control
  6. Methods Mol Biol. 2021 ;2277 143-155
      Mice missing the Complex I subunit NADH:Ubiquinone Oxidoreductase Fe-S Protein 4 (NDUFS4) of the electron transport chain are a leading model of the severe mitochondrial disease Leigh syndrome. These mice have enabled a better understanding of mitochondrial dysfunction in human disease, as well as in the discovery of interventions that can potentially suppress mitochondrial disease manifestations. In addition, increasing evidence suggests significant overlap between interventions that increase survival in NDUFS4 knockout mice and that extend life span during normative aging. This chapter discusses the practical aspects of handling and studying these mice, which can be challenging due to their severe disease phenotype. Common procedures such as breeding, genotyping, weaning, or treating these transgenic mice are also discussed.
    Keywords:  Aging; Complex I; Electron transport chain; Hypoxia; Leigh syndrome; Mitochondrial disease; Mitochondrial dysfunction; NAD; NDUFS4; Rapamycin; mTOR
  7. Methods Mol Biol. 2021 ;2276 227-234
      In mitochondrial oxidative phosphorylation (Ox-Phos), individual electron transport chain complexes are thought to assemble into supramolecular entities termed supercomplexes (SCs). The technique of blue native (BN) gel electrophoresis has emerged as the method of choice for analyzing SCs. However, the process of sample extraction for BN gel analysis is somewhat tedious and introduces the possibility for experimental artifacts. Here we outline a streamlined method that eliminates a centrifugation step and provides a more representative sampling of a population of mitochondria on the final gel. Using this method, we show that SC composition does not appear to change dynamically with altered mitochondrial function.
    Keywords:  Blue-native; Clear-native; Mitochondria; Permeability transition pore; Respiration; Supercomplexes
  8. Pharmaceutics. 2021 May 28. pii: 810. [Epub ahead of print]13(6):
      Mitochondria are intracellular energy generators involved in various cellular processes. Therefore, mitochondrial dysfunction often leads to multiple serious diseases, including neurodegenerative and cardiovascular diseases. A better understanding of the underlying mitochondrial dysfunctions of the molecular mechanism will provide important hints on how to mitigate the symptoms of mitochondrial diseases and eventually cure them. In this review, we first summarize the key parts of the genetic processes that control the physiology and functions of mitochondria and discuss how alterations of the processes cause mitochondrial diseases. We then list up the relevant core genetic components involved in these processes and explore the mutations of the components that link to the diseases. Lastly, we discuss recent attempts to apply multiple genetic methods to alleviate and further reverse the adverse effects of the core component mutations on the physiology and functions of mitochondria.
    Keywords:  gene therapy; heteroplasmy; mitochondrial DNA; mitochondrial disease; mitochondrial gene delivery
  9. Cells. 2021 May 29. pii: 1346. [Epub ahead of print]10(6):
      Numerous naturally occurring molecules have been studied for their beneficial health effects. Many compounds have received considerable attention for their potential medical uses. Among them, several substances have been found to improve mitochondrial function. This review focuses on resveratrol, (-)-epicatechin, and betaine and summarizes the published data pertaining to their effects on cytochrome c oxidase (COX) which is the terminal enzyme of the mitochondrial electron transport chain and is considered to play an important role in the regulation of mitochondrial respiration. In a variety of experimental model systems, these compounds have been shown to improve mitochondrial biogenesis in addition to increased COX amount and/or its enzymatic activity. Given that they are inexpensive, safe in a wide range of concentrations, and effectively improve mitochondrial and COX function, these compounds could be attractive enough for possible therapeutic or health improvement strategies.
    Keywords:  (–)-epicatechin; betaine; cytochrome c oxidase; mitochondrial biogenesis; oxidative phosphorylation; resveratrol
  10. Methods Mol Biol. 2021 ;2276 103-112
      Native electrophoresis is a powerful tool to analyze the mitochondrial electron transport chain complexes (Cx) I-V and their assembly into supercomplexes. Valuable information regarding the composition and bioenergetic regulation in physiological and pathological conditions can be obtained. This chapter compares different types of native electrophoresis to analyze mitochondrial supercomplexes.
    Keywords:  Mitochondrial supercomplexes; Native electrophoresis (blue native, colorless native, clear native, hybrid)
  11. Methods Mol Biol. 2021 ;2277 1-13
      Progress in animal modeling of polymorphisms and mutations in mitochondrial DNA (mtDNA) is not as developed as nuclear transgenesis due to a host of cellular and physiological distinctions. mtDNA mutation modeling is of critical importance as mutations in the mitochondrial genome give rise to a variety of pathological conditions and play a contributing role in many others. Nuclear localization and transcription of mtDNA genes followed by cytoplasmic translation and transport into mitochondria (allotopic expression, AE) provide an opportunity to create in vivo modeling of a targeted mutation in mitochondrial genes. Accordingly, such technology has been suggested as a strategy for gene replacement therapy in patients harboring mitochondrial DNA mutations. Here, we use our AE approach to transgenic mouse modeling of the pathogenic human T8993G mutation in mtATP6 as a case study for designing AE animal models.
    Keywords:  ATP6; Allotopic expression; Animal modeling; Mitochondrial disease; Transgenic mouse; mtDNA
  12. Trends Cell Biol. 2021 May 26. pii: S0962-8924(21)00095-7. [Epub ahead of print]
      Traditional culture media do not resemble the metabolic composition of human blood. The concentration of different metabolites in these media influences mitochondrial biogenesis and oxidative phosphorylation (OXPHOS) function. This knowledge is essential for the interpretation of results obtained from cellular models used for the study of OXPHOS function.
    Keywords:  cell culture media; cell model; mitochondrial biogenesis; oxidative phosphorylation