bims-cytox1 2023-10-15 papers

EMBO Rep. 2023 Oct 12. e57092

The functional significance of mitochondrial respiratory chain supercomplexes.

Andreas Kohler, Antoni Barrientos, Flavia Fontanesi, Martin Ott.

The mitochondrial respiratory chain (MRC) is a key energy transducer in eukaryotic cells. Four respiratory chain complexes cooperate in the transfer of electrons derived from various metabolic pathways to molecular oxygen, thereby establishing an electrochemical gradient over the inner mitochondrial membrane that powers ATP synthesis. This electron transport relies on mobile electron carries that functionally connect the complexes. While the individual complexes can operate independently, they are in situ organized into large assemblies termed respiratory supercomplexes. Recent structural and functional studies have provided some answers to the question of whether the supercomplex organization confers an advantage for cellular energy conversion. However, the jury is still out, regarding the universality of these claims. In this review, we discuss the current knowledge on the functional significance of MRC supercomplexes, highlight experimental limitations, and suggest potential new strategies to overcome these obstacles.

Keywords: Mitochondria; bioenergetics; electron transfer; respiratory chain; supercomplexes

DOI: https://doi.org/10.15252/embr.202357092

Nat Metab. 2023 Oct 09.

COX17 acetylation via MOF-KANSL complex promotes mitochondrial integrity and function.

Sukanya Guhathakurta, Niyazi Umut Erdogdu, Juliane J Hoffmann, Iga Grzadzielewska, Alexander Schendzielorz, Janine Seyfferth, Christoph U Mårtensson, Mauro Corrado, Adam Karoutas, Bettina Warscheid, Nikolaus Pfanner, Thomas Becker, Asifa Akhtar.

Reversible acetylation of mitochondrial proteins is a regulatory mechanism central to adaptive metabolic responses. Yet, how such functionally relevant protein acetylation is achieved remains unexplored. Here we reveal an unprecedented role of the MYST family lysine acetyltransferase MOF in energy metabolism via mitochondrial protein acetylation. Loss of MOF-KANSL complex members leads to mitochondrial defects including fragmentation, reduced cristae density and impaired mitochondrial electron transport chain complex IV integrity in primary mouse embryonic fibroblasts. We demonstrate COX17, a complex IV assembly factor, as a bona fide acetylation target of MOF. Loss of COX17 or expression of its non-acetylatable mutant phenocopies the mitochondrial defects observed upon MOF depletion. The acetylation-mimetic COX17 rescues these defects and maintains complex IV activity even in the absence of MOF, suggesting an activatory role of mitochondrial electron transport chain protein acetylation. Fibroblasts from patients with MOF syndrome who have intellectual disability also revealed respiratory defects that could be restored by alternative oxidase, acetylation-mimetic COX17 or mitochondrially targeted MOF. Overall, our findings highlight the critical role of MOF-KANSL complex in mitochondrial physiology and provide new insights into MOF syndrome.

DOI: https://doi.org/10.1038/s42255-023-00904-w

Elife. 2023 Oct 12. pii: RP88084. [Epub ahead of print]12

Structural rather than catalytic role for mitochondrial respiratory chain supercomplexes.

Michele Brischigliaro, Alfredo Cabrera-Orefice, Susanne Arnold, Carlo Viscomi, Massimo Zeviani, Erika Fernández-Vizarra.

Mammalian mitochondrial respiratory chain (MRC) complexes are able to associate into quaternary structures named supercomplexes (SCs), which normally coexist with non-bound individual complexes. The functional significance of SCs has not been fully clarified and the debate has been centered on whether or not they confer catalytic advantages compared with the non-bound individual complexes. Mitochondrial respiratory chain organization does not seem to be conserved in all organisms. In fact, and differently from mammalian species, mitochondria from Drosophila melanogaster tissues are characterized by low amounts of SCs, despite the high metabolic demands and MRC activity shown by these mitochondria. Here, we show that attenuating the biogenesis of individual respiratory chain complexes was accompanied by increased formation of stable SCs, which are missing in Drosophila melanogaster in physiological conditions. This phenomenon was not accompanied by an increase in mitochondrial respiratory activity. Therefore, we conclude that SC formation is necessary to stabilize the complexes in suboptimal biogenesis conditions, but not for the enhancement of respiratory chain catalysis.

Keywords: D. melanogaster; Drosophila; Mitochondria; OXPHOS; biochemistry; chemical biology; supercomplexes

DOI: https://doi.org/10.7554/eLife.88084