bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2019‒09‒15
five papers selected by
Gavin McStay
Staffordshire University

  1. Biol Chem. 2019 Sep 11. pii: /j/bchm.ahead-of-print/hsz-2019-0310/hsz-2019-0310.xml. [Epub ahead of print]
    Grevel A, Pfanner N, Becker T.
      Biogenesis and function of mitochondria depend on the import of about 1000 precursor proteins that are produced on cytosolic ribosomes. The translocase of the outer membrane (TOM) forms the entry gate for most proteins. After passage through the TOM channel, dedicated preprotein translocases sort the precursor proteins into the mitochondrial subcompartments. Many proteins have to be assembled into oligomeric membrane-integrated complexes in order to perform their functions. In this review, we discuss a dual role of mitochondrial preprotein translocases in protein translocation and oligomeric assembly, focusing on the biogenesis of the TOM complex and the respiratory chain. The sorting and assembly machinery (SAM) of the outer mitochondrial membrane forms a dynamic platform for coupling transport and assembly of TOM subunits. The biogenesis of the cytochrome c oxidase of the inner membrane involves a molecular circuit to adjust translation of mitochondrial-encoded core subunits to the availability of nuclear-encoded partner proteins. Thus, mitochondrial protein translocases not only import precursor proteins but can also support their assembly into functional complexes.
    Keywords:  TOM complex; mitochondria; protein assembly; protein import; respiratory chain
  2. ACS Chem Biol. 2019 Sep 09.
    Battersby BJ, Richter U, Safronov O.
      Proteotoxicity has long been considered a key factor in mitochondrial dysfunction and human disease. The origin of the endogenous offending toxic substrates and the regulatory pathways to deal with these insults, however, have remained unclear. Mitochondria maintain a compartmentalized gene expression system that in animals is only responsible for synthesis of 1% of the organelle proteome. Because of the relatively small contribution of the mitochondrial genome to the overall proteome, the synthesis and quality control of these nascent chains to maintain organelle proteostasis has long been overlooked. However, recent research has uncovered mechanisms by which defects to the quality control of mitochondrial gene expression are linked to a novel cellular stress response that impinges upon organelle form and function, and cell fitness. In this review, we discuss the mechanisms for a key event in the response: activation of the metalloprotease OMA1. This severs the membrane tether of the dynamin-related GTPase OPA1, which is a critical determinant for mitochondrial morphology and function. We also highlight the evolutionary conservation from bacteria of these quality control mechanisms to maintain membrane integrity, gene expression and cell fitness.
  3. Brain Dev. 2019 Sep 06. pii: S0387-7604(19)30287-6. [Epub ahead of print]
    Takada R, Tozawa T, Kondo H, Kizaki Z, Kishita Y, Okazaki Y, Murayama K, Ohtake A, Chiyonobu T.
      BACKGROUND: The mitochondrial DNA MT-ATP6 gene encodes the ATP6 subunit of the mitochondrial ATP synthase. The m.9185 T > C variant in MT-ATP6 has been reported to cause various neurological disorders including late-onset Leigh syndrome (LS). To our knowledge, there has been no reported case of infantile-onset LS associated with the m.9185 T > C variant. Herein, we report a patient with early-onset LS complicated with infantile spasms who exhibited profound developmental delay.CASE REPORT: A 3-month-old Japanese girl presented with focal seizures. Brain magnetic resonance imaging (MRI) revealed bilateral lesions in the basal ganglia and cerebral peduncle. Laboratory evaluation demonstrated marked elevations of lactate and pyruvate in both venous blood and cerebrospinal fluid. At 6 months, she developed infantile spasms, which were ceased by adrenocorticotropic hormone therapy. At 2 years of age, she was bedridden due to hypotonic quadriplegia and was unable to make eye contact. Whole-exome sequencing identified apparently de novo homoplasmic m.9185 T > C variant in her blood.
    CONCLUSION: This is the first case report describing early infantile-onset LS associated with the m.9185 T > C variant, and thereby broadens the phenotypic spectrum of m.9185 T > C-related disorders.
    Keywords:  Infantile spasms; Leigh syndrome; MTATP6; Mitochondrial DNA; m.9185T>C
  4. Life Sci Alliance. 2019 Oct;pii: e201900458. [Epub ahead of print]2(5):
    Maghool S, Cooray NDG, Stroud DA, Aragão D, Ryan MT, Maher MJ.
      Assembly factors play key roles in the biogenesis of many multi-subunit protein complexes regulating their stability, activity, and the incorporation of essential cofactors. The human assembly factor Coa6 participates in the biogenesis of the CuA site in complex IV (cytochrome c oxidase, COX). Patients with mutations in Coa6 suffer from mitochondrial disease due to complex IV deficiency. Here, we present the crystal structures of human Coa6 and the pathogenic W59CCoa6-mutant protein. These structures show that Coa6 has a 3-helical bundle structure, with the first 2 helices tethered by disulfide bonds, one of which likely provides the copper-binding site. Disulfide-mediated oligomerization of the W59CCoa6 protein provides a structural explanation for the loss-of-function mutation.
  5. Science. 2019 Sep 13. 365(6458): 1144-1149
    Saurer M, Ramrath DJF, Niemann M, Calderaro S, Prange C, Mattei S, Scaiola A, Leitner A, Bieri P, Horn EK, Leibundgut M, Boehringer D, Schneider A, Ban N.
      Mitochondrial ribosomes (mitoribosomes) are large ribonucleoprotein complexes that synthesize proteins encoded by the mitochondrial genome. An extensive cellular machinery responsible for ribosome assembly has been described only for eukaryotic cytosolic ribosomes. Here we report that the assembly of the small mitoribosomal subunit in Trypanosoma brucei involves a large number of factors and proceeds through the formation of assembly intermediates, which we analyzed by using cryo-electron microscopy. One of them is a 4-megadalton complex, referred to as the small subunit assemblosome, in which we identified 34 factors that interact with immature ribosomal RNA (rRNA) and recognize its functionally important regions. The assembly proceeds through large-scale conformational changes in rRNA coupled with successive incorporation of mitoribosomal proteins, providing an example for the complexity of the ribosomal assembly process in mitochondria.