bims-cytox1 2025-11-09 papers

Chemphyschem. 2025 Nov 08. e202500539

Proton-Coupled Electron Transfer in Cytochrome c Oxidase: Heme a Controls the Protonation Dynamics of E286.

Federico Baserga, Pit Langner, Luiz Schubert, Julian P Storm, Ramona Schlesinger, Joachim Heberle.

Complex IV of the mitochondrial respiratory chain, or cytochrome c oxidase (CcO), contributes to the proton motive force necessary for ATP synthesis. CcO can slow the formation of reactive oxygen species and is key to physiology and drug development. The exact molecular mechanisms underlying its proton-pumping function remain elusive. The redox state of CcO's metallic cofactors is intimately connected to structural changes and proton pumping via proton-coupled electron transfer. Time-resolved UV/Vis and IR spectroscopy are used to investigate the effects of the electronic backreaction triggered by photolyzing the CO-inhibited 2-electron reduced state, R2CO, in the aa3 oxidase from Cereibacter sphaeroides. An intermediate is identified, in which the binuclear center matches the redox state of the catalytic intermediate E (one-electron reduced state), with a rise time of ≈2 μs. The electron transfer induces structural changes that lead to E286 deprotonation, with a time constant of 13 μs. Thus, it is inferred that transient reduction of heme a alone drives E286 deprotonation. E286 is reprotonated with a time constant of 72 ms when CO rebinds. The results support the view that transient heme a reduction in the physiological E state modulates the electrostatic environment, triggering proton transfer toward the proton-loading site.

Keywords: electron transfers; oxidoreductases; photolysis; protonation; time‐resolved spectroscopy

DOI: https://doi.org/10.1002/cphc.202500539

Mitochondrion. 2025 Nov 05. pii: S1567-7249(25)00092-3. [Epub ahead of print] 102095

Complex IV deficiency due toCOX4I1deep intronic and de novo variants results in progressive motor impairment andLeigh syndrome.

Olatz Ugarteburu, Laia Farré-Tarrats, Gerard Muñoz-Pujol, María Unceta, Javier De Las Heras, Ainhoa Garcia-Ribes, Arantza Arza-Ruesga, Belén de la Morena, Gianluca Arauz-Garofalo, Marina Gay, Gloria Garrabou, Javier Corral, Marta Vilaseca, Antonia Ribes, Judit García-Villoria, Laura Gort, Frederic Tort.

COX4I1 gene encodes cytochrome c oxidase subunit 4 isoform 1, involved in the early assembly stages of mitochondrial respiratory chain complex IV. To date, COX4I1 pathogenic variants have been reported in only a few cases, each exhibiting heterogeneous clinical phenotypes and limited functional data. Here, we describe the fourth reported case of COX4I1 deficiency associated with human disease, expanding the phenotypic and genetic spectrum of this rare mitochondrial disorder and providing novel clinical, molecular, and functional data. The herein reported individual presented with progressive deterioration of motor skills, intellectual disability and brain imaging abnormalities compatible with Leigh syndrome. Genetic studies combining short and long read next generation sequencing uncovered a peculiar genetic combination in this patient, harboring a de novo COX4I1 nonsense substitution in trans with an inherited deep intronic variant (c.[64C>T];[73+1511A>G]; p.[Arg22Ter];[Glu25ValfsTer9]). Functional studies performed in patient's tissues and transiently transfected cell lines demonstrated that the identified variants mainly exert their pathogenic effect by targeting COX4I1 protein levels, thereby impairing the proper assembly and activity of complex IV.Additionally, proteomic data in patient's fibroblasts suggested an underlying pathomechanism that involves not only the regulation of complex IV function but also the levels of mitoribosomal proteins. In summary, our findings shed light to clarify some of the main clinical features associated with COX4I1 deficiency and the molecular mechanisms involved in the pathogenesis of this disorder.

Keywords: COX4I1; Leigh syndrome; Long read sequencing; Proteomics; complex IV

DOI: https://doi.org/10.1016/j.mito.2025.102095

J Cell Mol Med. 2025 Nov;29(21): e70922

Cytochrome c Oxidase Subunit 5A (COX5A) Enhances Gastric Cancer Progression by Augmenting ATP Synthesis and Activating the PI3K/Akt Pathway.

Dongyan Li, Limin Zhou.

Gastric cancer (GC) is a lethal malignancy characterised by poor prognosis. In this study, we identify cytochrome c oxidase subunit 5A (COX5A) as a key metabolic driver and prognostic biomarker in GC. COX5A was upregulated in tumours and correlated with poor survival. Mechanistically, COX5A enhanced mitochondrial oxidative phosphorylation to elevate ATP production, activating PI3K/Akt signalling to drive proliferation, migration, and invasion. These effects were reversed by PI3K/Akt inhibitors. JC-1 assays revealed COX5A-mediated mitochondrial membrane potential elevation, indicating amplified bioenergetic output. In vivo, COX5A silencing suppressed xenograft tumour growth. Our results demonstrate COX5A orchestrates metabolic reprogramming and PI3K/Akt-mediated progression in GC, positioning it as both a prognostic indicator and therapeutic target.

Keywords: ATP synthesis; COX5A; PI3K/Akt pathway; gastric cancer; mitochondrial function

DOI: https://doi.org/10.1111/jcmm.70922