bims-cytox1 2023-11-12 papers

Issue of 2023‒11‒12
four papers selected by
Gavin McStay, Liverpool John Moores University

Proc Natl Acad Sci U S A. 2023 Nov 14. 120(46): e2307697120

Structure and function of the S. pombe III-IV-cyt c supercomplex.

Agnes Moe, Anna-Roza Dimogkioka, Doron Rapaport, Linda Näsvik Öjemyr, Peter Brzezinski.

The respiratory chain in aerobic organisms is composed of a number of membrane-bound protein complexes that link electron transfer to proton translocation across the membrane. In mitochondria, the final electron acceptor, complex IV (CIV), receives electrons from dimeric complex III (CIII2), via a mobile electron carrier, cytochrome c. In the present study, we isolated the CIII2CIV supercomplex from the fission yeast Schizosaccharomyces pombe and determined its structure with bound cyt. c using single-particle electron cryomicroscopy. A respiratory supercomplex factor 2 was found to be bound at CIV distally positioned in the supercomplex. In addition to the redox-active metal sites, we found a metal ion, presumably Zn2+, coordinated in the CIII subunit Cor1, which is encoded by the same gene (qcr1) as the mitochondrial-processing peptidase subunit β. Our data show that the isolated CIII2CIV supercomplex displays proteolytic activity suggesting a dual role of CIII2 in S. pombe. As in the supercomplex from S. cerevisiae, subunit Cox5 of CIV faces towards one CIII monomer, but in S. pombe, the two complexes are rotated relative to each other by ~45°. This orientation yields equal distances between the cyt. c binding sites at CIV and at each of the two CIII monomers. The structure shows cyt. c bound at four positions, but only along one of the two symmetrical branches. Overall, this combined structural and functional study reveals the integration of peptidase activity with the CIII2 respiratory system and indicates a two-dimensional cyt. c diffusion mechanism within the CIII2-CIV supercomplex.

Keywords: bioenergetics; cytochrome bc1; cytochrome c oxidase; electron transfer; mitochondria

DOI: https://doi.org/10.1073/pnas.2307697120

Enzymes. 2023 ;pii: S1874-6047(23)00004-5. [Epub ahead of print]54 15-36

The mitochondrial respiratory chain.

Mårten Wikström, Cristina Pecorilla, Vivek Sharma.

We present a brief review of the mitochondrial respiratory chain with emphasis on complexes I, III and IV, which contribute to the generation of protonmotive force across the inner mitochondrial membrane, and drive the synthesis of ATP by the process called oxidative phosphorylation. The basic structural and functional details of these complexes are discussed. In addition, we briefly review the information on the so-called supercomplexes, aggregates of complexes I-IV, and summarize basic physiological aspects of cell respiration.

Keywords: Bioenergetics; Cell respiration; Cytochromes; Electron transfer; Oxidative phosphorylation; Oxygen consumption; Proton pumping; Proton transfer; Protonmotive force; Supercomplexes

DOI: https://doi.org/10.1016/bs.enz.2023.05.001

Am J Physiol Cell Physiol. 2023 Nov 06.

Microenvironmental stress drives tumor cell maladaptation and malignancy through regulation of mitochondrial and nuclear cytochrome c oxidase subunits.

Davide Gnocchi, Dragana Nikolic, Francesca Castellaneta, Rita R Paparella, Carlo Sabbà, Antonio Mazzocca.

After decades of focus on molecular genetics in cancer research, the role of metabolic and environmental factors is being reassessed. Here, we investigated the role of microenvironment in the promotion of malignant behavior in tumor cells with a different reliance on oxidative phosphorylation (OXPHOS) versus lactic acid fermentation/Warburg effect. To this end, we evaluated the effects of microenvironmental challenges (hypoxia, acidity, and high glucose) on the expression of mitochondrial-encoded cytochrome c oxidase 1 (COX I) and two nuclear-encoded isoforms 4 (COX IV-1 and COX IV-2). We have shown that tumor cells with an "OXPHOS phenotype" respond to hypoxia by upregulating COX IV-1, whereas cells that rely on lactic acid fermentation maximized COX IV-2 expression. Acidity upregulates COX IV-2 regardless of the metabolic state of the cell, whereas high glucose stimulates the expression of COX I and COX IV-1, with a stronger effect in fermenting cells. Our results uncover that "energy phenotype" of tumor cells drives their adaptive response to microenvironment stress.

Keywords: Tumor microenvironment; Warburg phenotype; cytochrome c oxidase subunits; malignancy; mitochondria

DOI: https://doi.org/10.1152/ajpcell.00508.2023

J Biol Chem. 2023 Nov 07. pii: S0021-9258(23)02463-8. [Epub ahead of print] 105435

Discovery of an unusual copper homeostatic mechanism in yeast cells respiring on minimal medium, and an unexpectedly diverse labile copper pool.

Joshua E Kim, Seoyoung Jeon, Paul A Lindahl.

Copper is essential for all eukaryotic cells but many details of how it is trafficked within the cell and how it is homeostatically regulated remain uncertain. Here, we characterized the copper content of cytosol and mitochondria using liquid chromatography with ICP-MS detection. Chromatograms of cytosol exhibited over 2 dozen peaks due to copper proteins and coordination complexes. Yeast cells respiring on minimal media didn't regulate copper import as media copper concentration increased; rather, they imported copper at increasing rates while simultaneously increasing expression of metallothionein CUP1 which then sequestered most of the excessive imported copper. Peak intensities due to superoxide dismutase SOD1, other copper proteins, and numerous coordination complexes also increased, but not as drastically. The labile copper pool was unexpectedly diverse and divided nicely into 2 groups. One group approximately comigrated with copper-glutathione, -cysteine, and -histidine standards; the other developed only at high media copper concentrations and at greater elution volumes. Most cytosolic copper arose from copper-bound proteins, especially CUP1. Cytosol contained an unexpectedly high percentage of apo-copper proteins and apo-coordination complexes. Copper-bound forms of non-CUP1 proteins and complexes coexisted with apo-CUP1 and with an excess of the chelator BCS. Both experiments suggest unexpectedly stable-binding copper proteins and coordination complexes in cytosol. COX17Δ cytosol chromatograms were like those of WT cells. Chromatograms of soluble mitochondrial extracts were obtained, and mitoplasting helped distinguish copper species in the intermembrane space vs. in the matrix/inner membrane. Issues involving the yeast copperome, copper homeostasis, the labile copper pool, and copper trafficking are discussed.

Keywords: COX17; CUP1; ICP-MS; Mössbauer spectroscopy; SOD1; copperome; cytochrome c oxidase; cytoplasm; glutathione; liquid chromatography; mitoplasts

DOI: https://doi.org/10.1016/j.jbc.2023.105435