bims-smemid 2026-08-16 papers

Protein Sci. 2026 Sep;35(9): e70763

Adaptation of OXPHOS biogenesis to cellular requirements.

Metabolic cues regulate the formation of the mitochondrial OXPHOS machinery. These regulatory processes are tightly linked to mitochondrial translation, proteolytic degradation of unassembled subunits, and the formation of supercomplexes, creating checkpoints at which nutrient availability, oxygen tension, and signaling pathways remodel OXPHOS content and activity. In particular, the cytochrome c oxidase (COX) assembly pathway is regulated at multiple steps of its biogenesis in response to cellular demands. COX consists of mitochondrially encoded catalytic core subunits and nuclear-encoded accessory subunits whose coordinated expression, cofactor insertion, and incorporation into the COX enzyme result in optimized electron transport capacity. Consequently, COX assembly depends on numerous dedicated factors and protein isoforms, many of which are expressed in a tissue-specific manner. Through these metabolically regulated processes, cells tune oxidative phosphorylation efficiency, limit reactive oxygen species production, and support context-specific metabolic programs in development, adaptation, and disease.

Keywords: Cytochrome c Oxidase; OXPHOS; mitochondria

DOI: https://doi.org/10.1002/pro.70763

EMBO Rep. 2026 Aug 14.

Polyunsaturated fatty acid sequestration protects against mitochondrial dysfunction-induced ferroptosis.

Impaired energy production is a hallmark of mitochondrial oxidative phosphorylation (OXPHOS) defects. However, secondary metabolic disturbances also represent an important trigger for pathologies originating from OXPHOS aberrations. Here we show that cells with OXPHOS deficiencies accumulate triacylglycerols enriched in polyunsaturated fatty acids (PUFAs), which are stored in lipid droplets. Sequestration of PUFAs is a critical component of a broader stress response, which also includes downregulation of cellular desaturases and upregulation of glutathione peroxidase 4 (GPX4). We demonstrate that this mechanism represents a physiologically relevant protective strategy, manifesting in cells under hypoxia and in immortalised fibroblasts derived from patients with primary mitochondrial complex IV deficiency. As a proof of principle, we observe elevated PUFA-enriched triacylglycerols in the plasma of patients with Myoclonic Epilepsy with Ragged Red Fibres (MERRF). Our findings reveal a novel protective mechanism against ferroptosis, which preserves membrane integrity when mitochondrial respiration is compromised.

DOI: https://doi.org/10.1038/s44319-026-00898-y

J Trace Elem Med Biol. 2026 Jul 28. pii: S0946-672X(26)00121-5. [Epub ahead of print]97 127935

Copper homeostasis and cuproptosis: New perspectives on the diagnosis and treatment of metabolic diseases.

Jing Chen, Chao Fang, Shiguo Tang, Haoran Wang.

Cuproptosis is a recently identified form of regulated cell death driven by the direct binding of Cu⁺ to the lipoyl moiety of mitochondrial tricarboxylic acid (TCA) cycle enzymes, leading to dihydrolipoamide S-acetyltransferase (DLAT) oligomerisation, iron-sulfur cluster (Fe-S) protein depletion, and proteotoxic stress, and is uniquely dependent on mitochondrial respiration. This review critically synthesises current evidence on the role of cuproptosis in type 2 diabetes mellitus (T2DM), metabolic dysfunction-associated steatotic liver disease (MASLD), and obesity. In T2DM, three causally validated pathways of copper transporter dysregulation converge on ferredoxin 1 (FDX1)-dependent DLAT oligomerisation, with substantial FDX1 reduction in diabetic skeletal muscle providing quantitative evidence of cuproptotic commitment; however, β-cell-specific knockout studies remain critically absent. In MASLD, indirect reactive oxygen species (ROS)-mediated insulin resistance is favoured over direct copper-receptor interactions. We propose the metabolic threshold hypothesis, positing that cuproptosis represents failed adaptation to chronic lipid overload, triggered when copper influx exceeds the combined buffering capacity of ATPase copper transporting beta (ATP7B)-mediated efflux, metallothionein sequestration, and glutathione (GSH) chelation. The serum Cu/Zn ratio cannot distinguish cuproptosis from ferroptosis; precise identification requires combined detection of FDX1, DLAT, lipoic acid synthase (LIAS), and lipoyltransferase 1 (LIPT1) with mitochondrial copper content, with immunohistochemistry (IHC) for DLAT oligomerisation as the most clinically accessible surrogate marker. Copper chelators including tetrathiomolybdate and merestinib are primary agents for metabolic tissue preservation, whereas ionophores such as elesclomol are restricted to oncology, with lipid nanoparticle-based delivery platforms essential to overcome the blood-brain barrier challenge, as underscored by the neurological worsening documented in D-penicillamine-treated Wilson disease patients. The interplay between cuproptosis and ferroptosis, sharing GSH depletion but diverging at lipoylated protein aggregation versus glutathione peroxidase 4 (GPX4)-dependent lipid peroxidation, suggests dual-pathway inhibition may be necessary. Future priorities include validation of the metabolic threshold hypothesis, β-cell-specific knockout studies, standardised DLAT oligomerisation diagnostics, tissue-targeted copper modulator delivery, and integration of cuproptosis biomarkers with multi-omics and artificial intelligence for clinically stratified precision medicine.

Keywords: Copper homeostasis; Cuproptosis; Lipoylated proteins; Metabolic diseases

DOI: https://doi.org/10.1016/j.jtemb.2026.127935

Mitochondrion. 2026 Aug 04. pii: S1567-7249(26)00088-7. [Epub ahead of print]91 102198

Role of Coa6 in coordinating Cox2 and cytochrome c maturation in yeast mitochondria.

Geneviève Dujardin, Anaïs Lalève, Mathilde Logerais, Cristina Panozzo, David Cornu, Alexa Bourand-Plantefol, Virginie Chiodelli, Patrice Hamel, Nathalie Bonnefoy.

Coa6 controls copper delivery into the Cox2 subunit of the mitochondrial respiratory complex IV. Mutations in COA6 lead to Cox2 degradation and cause cardiomyopathy in humans. We show that decreasing the level of the mobile electron transporter cytochrome c improves both Cox2 accumulation and complex IV assembly in the budding yeast coa6-null mutant. As the heme attachment to apo-cytochrome c and the copper delivery to apo-Cox2 both require cysteine reduction, we propose that Coa6 plays a role in coordinating the maturation of Cox2 and Cytc with their cofactors.

Keywords: Apo-protein maturation; Copper delivery; Cox2 subunit; Cytochrome c; Heme attachment; Saccharomyces cerevisiae, mitochondria

DOI: https://doi.org/10.1016/j.mito.2026.102198

Bio Protoc. 2026 Aug 05. 16(15): e5768

Coupled Enzyme Assay for Measuring Ornithine Decarboxylase Activity in Cell Lysates Using a Liquid-Stable CO2 Detection Reagent.

Jung-Mao Hsu.

Ornithine decarboxylase (ODC) is a rate-limiting enzyme in polyamine biosynthesis that plays a critical role in cell proliferation and tumorigenesis. Reliable quantification of ODC activity is essential for mechanistic and therapeutic studies. Traditional assays often rely on radiolabeled substrates or discontinuous endpoint measurements. Here, we describe a non-radioactive, continuous spectrophotometric assay for measuring ODC activity in cell lysates using a commercially available liquid-stable CO2 detection reagent. In this assay, CO2 generated by ODC is captured as bicarbonate and utilized in a coupled enzymatic system containing phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH), leading to oxidation of thio-NADH. The decrease in absorbance at 405 nm due to thio-NADH oxidation is monitored in real time and is proportional to ODC activity. The protocol is performed in a 96-well plate format, requires minimal reagent preparation, and is suitable for medium- to high-throughput applications. Key features • Non-radioactive, continuous assay for measuring ODC activity. • Utilizes a commercially available liquid-stable CO2 detection reagent, requiring minimal preparation and enabling improved reproducibility. • Real-time monitoring at 405 nm using a standard microplate reader. • Adaptable to a high-throughput 96-well format.

Keywords: CO2 detection; Enzyme assay; Malate dehydrogenase (MDH); Ornithine decarboxylase (ODC); Phosphoenolpyruvate carboxylase (PEPC); Polyamine metabolism; Reduced form (thio-NADH); Thionicotinamide adenine dinucleotide

DOI: https://doi.org/10.21769/BioProtoc.5768

RSC Chem Biol. 2026 Jul 10.

The KDM6 histone H3K27me3 demethylase inhibitor GSK-J4 induces metal and stress responses in multiple myeloma cells.

Thioneins are cysteine-rich apoproteins that regulate divalent metal homeostasis by virtue of their metal-chelation properties resulting in the ligand-bound metallothionein state. Previous studies show transient upregulation of the metallothionein (MT) gene cluster as part of a complex transcriptional response to a class of histone H3K27me3 demethylase tool compounds targeting human Fe2+ dependent ketoglutarate oxygenases KDM6A (UTX) and KDM6B (JmjD3). The prototypic bioactive KDM6 inhibitor GSK-J4 induces apoptotic cell death in multiple myeloma cells and corresponding transcriptomic profiles are dominated by metal and integrated stress response (ISR) signatures, also observed in primary human myeloma cells. Here we investigate the hypothesis that metal-chelation by GSK-J4 provides the means for transport and intracellular release of Zn2+ leading to a metallothionein transcriptomic response signature. Live cell imaging of myeloma cells shows transient increases in intracellular free Zn2+ concentrations when exposed to GSK-J4, consistent with a model of inhibitor-mediated metal transport, further supported by direct metal-inhibitor complex formation as determined by MALDI-TOF mass spectrometry and 1H NMR. Comparisons of GSK-J4 and ZnSO4 treatments in the presence or absence of metal chelators show that both treatment conditions induce different transcription factor repertoires with an overlapping MTF1 transcriptional regulation responsible for metallothionein and metal ion transport regulation. The data provide a possible explanation for the observed metal response upon GSK-J4 inhibition however the relationship with the pro-apoptotic ISR mechanism in myeloma cells requires further investigation.

DOI: https://doi.org/10.1039/d6cb00162a