bims-resufa 2020-01-12 papers

Issue of 2020–01–12
three papers selected by
Vera Strogolova, Marquette University

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

Protein Cell. 2020 Jan 09.

Research journey of respirasome.

Meng Wu, Jinke Gu, Shuai Zong, Runyu Guo, Tianya Liu, Maojun Yang.

Respirasome, as a vital part of the oxidative phosphorylation system, undertakes the task of transferring electrons from the electron donors to oxygen and produces a proton concentration gradient across the inner mitochondrial membrane through the coupled translocation of protons. Copious research has been carried out on this lynchpin of respiration. From the discovery of individual respiratory complexes to the report of the high-resolution structure of mammalian respiratory supercomplex I1III2IV1, scientists have gradually uncovered the mysterious veil of the electron transport chain (ETC). With the discovery of the mammalian respiratory mega complex I2III2IV2, a new perspective emerges in the research field of the ETC. Behind these advances glitters the light of the revolution in both theory and technology. Here, we give a short review about how scientists 'see' the structure and the mechanism of respirasome from the macroscopic scale to the atomic scale during the past decades.

Keywords: cellular respiration; cryo-EM; electron transport chain; megacomplex; structure of respirasome; supercomplex organization

DOI: https://doi.org/10.1007/s13238-019-00681-x

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