bims-cytox1 2020-01-12 papers

Issue of 2020–01–12
four papers selected by
Gavin McStay, Staffordshire University

EMBO J. 2020 Jan 08. e102817

Respiratory supercomplexes act as a platform for complex III-mediated maturation of human mitochondrial complexes I and IV.

Margherita Protasoni, Rafael Pérez-Pérez, Teresa Lobo-Jarne, Michael E Harbour, Shujing Ding, Ana Peñas, Francisca Diaz, Carlos T Moraes, Ian M Fearnley, Massimo Zeviani, Cristina Ugalde, Erika Fernández-Vizarra.

Mitochondrial respiratory chain (MRC) enzymes associate in supercomplexes (SCs) that are structurally interdependent. This may explain why defects in a single component often produce combined enzyme deficiencies in patients. A case in point is the alleged destabilization of complex I in the absence of complex III. To clarify the structural and functional relationships between complexes, we have used comprehensive proteomic, functional, and biogenetical approaches to analyze a MT-CYB-deficient human cell line. We show that the absence of complex III blocks complex I biogenesis by preventing the incorporation of the NADH module rather than decreasing its stability. In addition, complex IV subunits appeared sequestered within complex III subassemblies, leading to defective complex IV assembly as well. Therefore, we propose that complex III is central for MRC maturation and SC formation. Our results challenge the notion that SC biogenesis requires the pre-formation of fully assembled individual complexes. In contrast, they support a cooperative-assembly model in which the main role of complex III in SCs is to provide a structural and functional platform for the completion of overall MRC biogenesis.

Keywords: complex I; complex III; cytochrome b mutation; mitochondrial respiratory chain assembly; supercomplexes

DOI: https://doi.org/10.15252/embj.2019102817

Folia Biol (Praha). 2019 ;65(4): 181-187

Stable COX17 Downregulation Leads to Alterations in Mitochondrial Ultrastructure, Decreased Copper Content and Impaired Cytochrome c Oxidase Biogenesis in HEK293 Cells.

M Vanišová, D Burská, J Křížová, T Daňhelovská, Ž Dosoudilová, J Zeman, L Stibůrek, H Hansíková.

Cox17 is an assembly factor that participates in early cytochrome c oxidase (COX, CcO) assembly stages. Cox17 shuttles copper ions from the cytosol to the mitochondria and, together with Sco1 and Sco2, provides copper ions to the Cox1 and Cox2 mitochondrially encoded subunits. In Saccharomyces cerevisiae, Cox17 also modulates mitochondrial membrane architecture due to the interaction of Cox17 with proteins of the MICOS complex (mitochondrial contact site and cristae organizing system). There is currently no data regarding the impact of long-term Cox17 deficiency in human cells. Here, we present construction and characterization of three stable COX17 shRNA-downregulated HEK293 cell lines that have less than 10 % of the residual Cox17 protein level. Cox17-depleted cell lines exhibited decreased intramitochondrial copper content, decreased CcO subunit levels (Cox1, Cox4 and Cox5a) and accumulation of CcO subcomplexes. Similarly to yeast cells, mitochondria in Cox17-downregulated HEK293 cell lines exhibited ultrastructural changes including cristae reduction and mitochondrial swelling. Characterization of the molecular pathogenesis of long-term Cox17 deficiency complements our knowledge of the mitochondrial copper metabolism and assembly of cytochrome c oxidase in human cells.

Sci Adv. 2019 Dec;5(12): eaay2118

Fidelity of translation initiation is required for coordinated respiratory complex assembly.

Danielle L Rudler, Laetitia A Hughes, Kara L Perks, Tara R Richman, Irina Kuznetsova, Judith A Ermer, Laila N Abudulai, Anne-Marie J Shearwood, Helena M Viola, Livia C Hool, Stefan J Siira, Oliver Rackham, Aleksandra Filipovska.

Mammalian mitochondrial ribosomes are unique molecular machines that translate 11 leaderless mRNAs; however, it is not clear how mitoribosomes initiate translation, since mitochondrial mRNAs lack untranslated regions. Mitochondrial translation initiation shares similarities with prokaryotes, such as the formation of a ternary complex of fMet-tRNAMet, mRNA and the 28S subunit, but differs in the requirements for initiation factors. Mitochondria have two initiation factors: MTIF2, which closes the decoding center and stabilizes the binding of the fMet-tRNAMet to the leaderless mRNAs, and MTIF3, whose role is not clear. We show that MTIF3 is essential for survival and that heart- and skeletal muscle-specific loss of MTIF3 causes cardiomyopathy. We identify increased but uncoordinated mitochondrial protein synthesis in mice lacking MTIF3, resulting in loss of specific respiratory complexes. Ribosome profiling shows that MTIF3 is required for recognition and regulation of translation initiation of mitochondrial mRNAs and for coordinated assembly of OXPHOS complexes in vivo.

DOI: https://doi.org/10.1126/sciadv.aay2118

FASEB J. 2020 Jan;34(1): 1859-1871

Higd1a improves respiratory function in the models of mitochondrial disorder.

Takemasa Nagao, Yasunori Shintani, Takaharu Hayashi, Hidetaka Kioka, Hisakazu Kato, Yuya Nishida, Satoru Yamazaki, Osamu Tsukamoto, Shohei Yashirogi, Issei Yazawa, Yoshihiro Asano, Kyoko Shinzawa-Itoh, Hiromi Imamura, Takeo Suzuki, Tsutomu Suzuki, Yu-Ichi Goto, Seiji Takashima.

The respiratory chain (RC) transports electrons to form a proton motive force that is required for ATP synthesis in the mitochondria. RC disorders cause mitochondrial diseases that have few effective treatments; therefore, novel therapeutic strategies are critically needed. We previously identified Higd1a as a positive regulator of cytochrome c oxidase (CcO) in the RC. Here, we test that Higd1a has a beneficial effect by increasing CcO activity in the models of mitochondrial dysfunction. We first demonstrated the tissue-protective effects of Higd1a via in situ measurement of mitochondrial ATP concentrations ([ATP]mito) in a zebrafish hypoxia model. Heart-specific Higd1a overexpression mitigated the decline in [ATP]mito under hypoxia and preserved cardiac function in zebrafish. Based on the in vivo results, we examined the effects of exogenous HIGD1A on three cellular models of mitochondrial disease; notably, HIGD1A improved respiratory function that was coupled with increased ATP synthesis and demonstrated cellular protection in all three models. Finally, enzyme kinetic analysis revealed that Higd1a significantly increased the maximal velocity of the reaction between CcO and cytochrome c without changing the affinity between them, indicating that Higd1a is a positive modulator of CcO. These results corroborate that Higd1a, or its mimic, provides therapeutic options for the treatment of mitochondrial diseases.

Keywords: cytochrome c oxidase; hypoxia; mitochondria; respiratory chain

DOI: https://doi.org/10.1096/fj.201800389R