bims-cytox1 2022-03-27 papers

Issue of 2022–03–27
four papers selected by
Gavin McStay, Staffordshire University

Genes (Basel). 2022 Feb 25. pii: 424. [Epub ahead of print]13(3):

COX4-like, a Nuclear-Encoded Mitochondrial Gene Duplicate, Is Essential for Male Fertility in Drosophila melanogaster.

Mohammadmehdi Eslamieh, Ayda Mirsalehi, Dragomira N Markova, Esther Betrán.

Recent studies on nuclear-encoded mitochondrial genes (N-mt genes) in Drosophila melanogaster have shown a unique pattern of expression for newly duplicated N-mt genes, with many duplicates having a testis-biased expression and playing an essential role in spermatogenesis. In this study, we investigated a newly duplicated N-mt gene-i.e., Cytochrome c oxidase 4-like (COX4L)-in order to understand its function and, consequently, the reason behind its retention in the D. melanogaster genome. The COX4L gene is a duplicate of the Cytochrome c oxidase 4 (COX4) gene of OXPHOS complex IV. While the parental COX4 gene has been found in all eukaryotes, including single-cell eukaryotes such as yeast, we show that COX4L is only present in the Brachycera suborder of Diptera; thus, both genes are present in all Drosophila species, but have significantly different patterns of expression: COX4 is highly expressed in all tissues, while COX4L has a testis-specific expression. To understand the function of this new gene, we first knocked down its expression in the D. melanogaster germline using two different RNAi lines driven by the bam-Gal4 driver; second, we created a knockout strain for this gene using CRISPR-Cas9 technology. Our results showed that knockdown and knockout lines of COX4L produce partial sterility and complete sterility in males, respectively, where a lack of sperm individualization was observed in both cases. Male infertility was prevented by driving COX4L-HA in the germline, but not when driving COX4-HA. In addition, ectopic expression of COX4L in the soma caused embryonic lethality, while overexpression in the germline led to a reduction in male fertility. COX4L-KO mitochondria show reduced membrane potential, providing a plausible explanation for the male sterility observed in these flies. This prominent loss-of-function phenotype, along with its testis-biased expression and its presence in the Drosophila sperm proteome, suggests that COX4L is a paralogous, specialized gene that is assembled in OXPHOS complex IV of male germline cells and/or sperm mitochondria.

Keywords: COX4L; CRISPR knockout; Drosophila melanogaster; gene duplication; nuclear-encoded mitochondrial gene; spermatogenesis

DOI: https://doi.org/10.3390/genes13030424

Curr Opin Cell Biol. 2022 Mar 17. pii: S0955-0674(22)00016-3. [Epub ahead of print]75 102071

Fidelity of organellar protein targeting.

Jiyao Song, Thomas Becker.

The majority of cellular proteins are targeted to organelles. Cytosolic ribosomes produce these proteins as precursors with cleavable or non-cleavable targeting sequences that direct them to receptor proteins on the organelle surface. Multiple targeting factors ensure cellular sorting of the precursor proteins. In co-translational protein import, the ribosome-nascent chain complex is transported to the organellar protein translocase to couple protein synthesis and protein import. In post-translational mode, targeting factors like molecular chaperones guide the precursor proteins from ribosomes to the cell organelle. Defects in protein targeting and import cause mistargeting of proteins to different cellular compartments and challenge the balance of cellular proteostasis. Specific dislocases and degradation machineries remove such mislocalized proteins from the membrane to allow retargeting or their proteasomal turnover. In this review, we discuss targeting and quality control factors that ensure fidelity of protein targeting to mitochondria.

DOI: https://doi.org/10.1016/j.ceb.2022.02.005

Mol Cell. 2022 Mar 11. pii: S1097-2765(22)00167-8. [Epub ahead of print]

Quality control of protein complex composition.

Chris Padovani, Predrag Jevtić, Michael Rapé.

Eukaryotic cells possess hundreds of protein complexes that contain multiple subunits and must be formed at the correct time and place during development. Despite specific assembly pathways, cells frequently encounter complexes with missing or aberrant subunits that can disrupt important signaling events. Cells, therefore, employ several ubiquitin-dependent quality control pathways that can prevent, correct, or degrade flawed complexes. In this review, we will discuss our emerging understanding of such quality control of protein complex composition.

Keywords: aneuploidy; dimerization quality control; orphan quality control; proteasome; quality control; ubiquitin; ubiquitylation

DOI: https://doi.org/10.1016/j.molcel.2022.02.029

Cells. 2022 Mar 14. pii: 992. [Epub ahead of print]11(6):

Cytochrome c Oxidase Inhibition by ATP Decreases Mitochondrial ROS Production.

Rabia Ramzan, Amalia M Dolga, Susanne Michels, Petra Weber, Carsten Culmsee, Ardawan J Rastan, Sebastian Vogt.

This study addresses the eventual consequence of cytochrome c oxidase (CytOx) inhibition by ATP at high ATP/ADP ratio in isolated rat heart mitochondria. Earlier, it has been demonstrated that the mechanism of allosteric ATP inhibition of CytOx is one of the key regulations of mitochondrial functions. It is relevant that aiming to maintain a high ATP/ADP ratio for the measurement of CytOx activity effectuating the enzymatic inhibition as well as mitochondrial respiration, optimal concentration of mitochondria is critically important. Likewise, only at this concentration, were the differences in ΔΨm and ROS concentrations measured under various conditions significant. Moreover, when CytOx activity was inhibited in the presence of ATP, mitochondrial respiration and ΔΨm both remained static, while the ROS production was markedly decreased. Consubstantial results were found when the electron transport chain was inhibited by antimycin A, letting only CytOx remain functional to support the energy production. This seems to corroborate that the decrease in mitochondrial ROS production is solely the effect of ATP binding to CytOx which results in static respiration as well as membrane potential.

Keywords: ATP; ROS; cytochrome c oxidase; mitochondrial membrane potential

DOI: https://doi.org/10.3390/cells11060992