bims-resufa 2022-08-14 papers

Issue of 2022–08–14
three papers selected by
Vera Strogolova, Strong Microbials, Inc

Trends Biochem Sci. 2022 Aug 09. pii: S0968-0004(22)00187-6. [Epub ahead of print]

Cooperative assembly of the mitochondrial respiratory chain.

Erika Fernández-Vizarra, Cristina Ugalde.

Deep understanding of the pathophysiological role of the mitochondrial respiratory chain (MRC) relies on a well-grounded model explaining how its biogenesis is regulated. The lack of a consistent framework to clarify the modes and mechanisms governing the assembly of the MRC complexes and supercomplexes (SCs) works against progress in the field. The plasticity model was postulated as an attempt to explain the coexistence of mammalian MRC complexes as individual entities and associated in SC species. However, mounting data accumulated throughout the years question the universal validity of the plasticity model as originally proposed. Instead, as we argue here, a cooperative assembly model provides a much better explanation to the phenomena observed when studying MRC biogenesis in physiological and pathological settings.

Keywords: assembly factors; cooperative assembly model; mitochondria; plasticity model; respiratory chain organization; supercomplexes

DOI: https://doi.org/10.1016/j.tibs.2022.07.005

Biochim Biophys Acta Bioenerg. 2022 Aug 08. pii: S0005-2728(22)00379-6. [Epub ahead of print] 148909

High efficient cyclic electron flow and functional supercomplexes in Chlamydomonas cells.

Pierre Joliot, Julien Sellés, Françis-André Wollman, André Verméglio.

A very high rate for cyclic electron flow (CEF) around PSI (~180 s-1 or 210 s-1 in minimum medium or in the presence of a carbon source respectively) is measured in the presence of methyl viologen (MV) in intact cells of Chlamydomonas reinhardtii under anaerobic conditions. The observation of an efficient CEF in the presence of methyl viologen is in agreement with the previous results reports of Asada et al. in broken chloroplasts (Plant Cell Physiol. 31(4) (1990) 557-564). From the analysis of the P700 and PC absorbance changes, we propose that a confinement between 2 PC molecules, 1 PSI and 1 cytb6f corresponding to a functional supercomplex is responsible for these high rates of CEF. Supercomplex formation is also observed in the absence of methyl viologen, but with lower maximal CEF rate (about 100 s-1) suggesting that this compound facilitates the mediation of electron transfer from PSI acceptors to the stromal side of cytb6f. Further analysis of CEF in mutants of Chlamydomonas defective in state transitions shows the requirement of a kinase-driven transition to state 2 to establish this functional supercomplex configuration. However, a movement of the LHCII antennae is not involved in this process. We discuss the possible involvement of auxiliary proteins, among which is a small cytb6f-associated polypeptide, the PETO protein, which is one of the targets of the STT7 kinase.

Keywords: Cyclic electron transfer; Cytochrome b(6)f; Methyl viologen; PSI; Supercomplex

DOI: https://doi.org/10.1016/j.bbabio.2022.148909

Genome Biol. 2022 Aug 09. 23(1): 170

Balanced mitochondrial and cytosolic translatomes underlie the biogenesis of human respiratory complexes.

Iliana Soto, Mary Couvillion, Katja G Hansen, Erik McShane, J Conor Moran, Antoni Barrientos, L Stirling Churchman.

BACKGROUND: Oxidative phosphorylation (OXPHOS) complexes consist of nuclear and mitochondrial DNA-encoded subunits. Their biogenesis requires cross-compartment gene regulation to mitigate the accumulation of disproportionate subunits. To determine how human cells coordinate mitochondrial and nuclear gene expression processes, we tailored ribosome profiling for the unique features of the human mitoribosome.
RESULTS: We resolve features of mitochondrial translation initiation and identify a small ORF in the 3' UTR of MT-ND5. Analysis of ribosome footprints in five cell types reveals that average mitochondrial synthesis levels correspond precisely to cytosolic levels across OXPHOS complexes, and these average rates reflect the relative abundances of the complexes. Balanced mitochondrial and cytosolic synthesis does not rely on rapid feedback between the two translation systems, and imbalance caused by mitochondrial translation deficiency is associated with the induction of proteotoxicity pathways.
CONCLUSIONS: Based on our findings, we propose that human OXPHOS complexes are synthesized proportionally to each other, with mitonuclear balance relying on the regulation of OXPHOS subunit translation across cellular compartments, which may represent a proteostasis vulnerability.

DOI: https://doi.org/10.1186/s13059-022-02732-9