bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2022‒05‒29
three papers selected by
Gavin McStay
Staffordshire University

  1. Microorganisms. 2022 Apr 28. pii: 926. [Epub ahead of print]10(5):
      Cytochrome c oxidase in animals, plants and many aerobic bacteria functions as the terminal enzyme of the respiratory chain where it reduces molecular oxygen to form water in a reaction coupled to energy conservation. The three-subunit core of the enzyme is conserved, whereas several proteins identified to function in the biosynthesis of the common family A1 cytochrome c oxidase show diversity in bacteria. Using the model organisms Bacillus subtilis, Corynebacterium glutamicum, Paracoccus denitrificans, and Rhodobacter sphaeroides, the present review focuses on proteins for assembly of the heme a, heme a3, CuB, and CuA metal centers. The known biosynthesis proteins are, in most cases, discovered through the analysis of mutants. All proteins directly involved in cytochrome c oxidase assembly have likely not been identified in any organism. Limitations in the use of mutants to identify and functionally analyze biosynthesis proteins are discussed in the review. Comparative biochemistry helps to determine the role of assembly factors. This information can, for example, explain the cause of some human mitochondrion-based diseases and be used to find targets for new antimicrobial drugs. It also provides information regarding the evolution of aerobic bacteria.
    Keywords:  bioenergetics; copper protein; cytochrome oxidase; enzyme assembly factors; enzyme biosynthesis; heme protein
  2. Clin Neuropathol. 2022 May 23.
      OBJECTIVE: Spinocerebellar ataxia with axonal neuropathy type 3 (SCAN3) is a very rare autosomal recessive hereditary disease. Mutations in the COA7 gene, which encodes cytochrome c oxidase assembly factor 7, have been recently reported as the causative gene of SCAN3. So far, only five SCAN3 patients with COA7 mutations have been documented. Herein, we report the clinical, electrophysiological, histological, and genetic findings of a Chinese patient with SCAN3.MATERIALS AND METHODS: The patient was a 31-year-old woman who presented with early-onset peripheral neuropathy and progressive ataxia. She was asked about her medical history and underwent electrophysiological examination, nerve and muscle biopsy, and gene detection.
    RESULTS: Whole exome next-generation sequencing identified a novel compound heterozygous mutation of COA7 (c.17A>G p.D6G; c.554G>A, p.W185*) in this patient. Magnetic resonance imaging showed cerebellum and spinal cord atrophy. Nerve conduction studies and sural nerve biopsies revealed sensorimotor axonal neuropathy. Muscle biopsies showed mitochondrial abnormalities. Respiratory chain enzyme assay of skin fibroblasts showed normal respiratory chain complex activities. Additionally, the clinical data on previously reported SCAN patients with identified genetic causes in PubMed was summarized. Compared with SCAN1 and SCAN2 patients, SCAN3 patients had earlier onset age, less cognitive impairment, and no ocular signs.
    CONCLUSION: We reported the first patient diagnosed with SCAN3 in China. A novel mutation in the gene COA7 (c.554G>A, p.W185*) expanded the genetic spectrum of the disease.
  3. Biomol Concepts. 2022 May 26. 13(1): 272-288
      Following structural determination by recent advances in electron cryomicroscopy, it is now well established that the respiratory Complexes I-IV in oxidative phosphorylation (OXPHOS) are organized into supercomplexes in the respirasome. Nonetheless, the reason for the existence of the OXPHOS supercomplexes and their functional role remains an enigma. Several hypotheses have been proposed for the existence of these supercomplex supercomplexes. A commonly-held view asserts that they enhance catalysis by substrate channeling. However, this - and other views - has been challenged based on structural and biophysical information. Hence, new ideas, concepts, and frameworks are needed. Here, a new model of energy transfer in OXPHOS is developed on the basis of biochemical data on the pure competitive inhibition of anionic substrates like succinate by the classical anionic uncouplers of OXPHOS (2,4-dinitrophenol, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, and dicoumarol), and pharmacological data on the unique site-selective, energy-linked inhibition of energy conservation pathways in mitochondria induced by the guanidine derivatives. It is further found that uncouplers themselves are site-specific and exhibit differential selectivity and efficacy in reversing the inhibition caused by the Site 1/Complex I or Site 2/Complexes II-III-selective guanidine derivatives. These results lead to new vistas and sufficient complexity in the network of energy conservation pathways in the mitochondrial respiratory chain that necessitate discrete points of interaction with two classes of guanidine derivatives and uncoupling agents and thereby separate and distinct energy transfer pathways between Site 1 and Site 2 and the intermediate that energizes adenosine triphosphate (ATP) synthesis by Complex V. Interpretation based on Mitchell's single-ion chemiosmotic theory that postulates only a single energy pool is inadequate to rationalize the data and account for the required complexity. The above results and available information are shown to be explained by Nath's two-ion theory of energy coupling and ATP synthesis, involving coupled movement of succinate anions and protons, along with the requirement postulated by the theory for maintenance of homeostasis and ion translocation across the energy-transducing membrane of both succinate monoanions and succinate dianions by Complexes I-V in the OXPHOS supercomplexes. The new model of energy transfer in mitochondria is mapped onto the solved structures of the supercomplexes and integrated into a consistent model with the three-dimensional electron microscope computer tomography visualization of the internal structure of the cristae membranes in mammalian mitochondria. The model also offers valuable insights into diseased states induced in type 2 diabetes and especially in Alzheimer's and other neurodegenerative diseases that involve mitochondrial dysfunction.
    Keywords:  2,4-dinitrophenol; Alzheimer’s disease; Complexes I–V; Gunnar Hollunger’s pioneering work in pharmacology; Mitchell’s single-ion chemiosmotic theory; Nath’s torsional mechanism of energy transduction and ATP synthesis; Nath’s two-ion theory of energy coupling; OXPHOS supercomplexes; Paolo Bernardi’s pioneering work on cell death and ATP; alkylguanidines; carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; competitive inhibition of succinate with the anionic uncouplers of OXPHOS; coupling of proton and succinate anion transport; dicoumarol; differential release of inhibition by pharmacological agents by uncouplers; functional role of the OXPHOS supercomplexes; inhibition of succinate entry by uncouplers; integrated mitochondrial function; interaction of site-specific guanidine derivatives with mitochondria; mitochondrial dysfunction; new definition of mitochondrial respiration; new model of energy transfer in mitochondria; octylguanidines; oxidative phosphorylation; phenethylbiguanides; sensing of local electrical potential, Δψ; supramolecular biology; supramolecular chemistry; translocation of succinate monoanions and succinate dianions across cristae membranes; two distinct energy conservation pathways between the electron transport chain and FOF1-ATP synthase; type 2 diabetes