Chagas, J. A. | bioRxiv Science

bioRxiv2026

The mitoribosome-associated factor Mrx9 acts as a negative regulator of the prohibitin/m-AAA complex

The synthesis of mitochondrial-encoded polypeptides is an essential process, primarily regulated at the posttranscriptional level. In yeast, many regulatory factors have been described as acting in proximity to the mitoribosome to promote efficient translation; however, the precise mechanisms by which these components function remain largely unknown. Here, we expand on findings concerning a previously studied mitoribosome interactor, Mrx9, which is found in large expressosome-like assemblies of mitoribosome clusters. Mrx9 was initially linked to mitochondrial translation and was suggested to be associated with the splicing of COX1 and COB transcripts. Our current data show that Mrx9 is associated with the PHB/m-AAA complex at the polypeptide exit tunnel of the mitoribosome. Overexpression of Mrx9 impairs the proteolytic functions of Yta10 and Yta12 within the prohibitin complex, leading to splicing defects; accumulation of aberrant polypeptides; and a noticeable impairment in the processing of the essential mitoribosomal protein bL32m. These findings support a regulatory role for Mrx9 in the PHB/m-AAA complex by modulating the activities of both Yta10 and Yta12.

molecular biology↗

bioRxiv2023

Dmo2p is required for Cox2p stability and plays a role in mitochondrial redox balance.

Based on available platforms of Saccharomyces cerevisiae mitochondrial proteome and other high throughput studies, we identified the yeast gene DMO2 with a profile of genetic and physical interactions that indicate a putative role in mitochondrial respiration. Dmo2p is a homolog to human DMAC1 with two conserved cysteines in a Cx2C motif. Here, we localized Dmo2p in the mitochondrial inner membrane with the conserved cysteines facing the intermembrane space. The observed phenotypes of the dmo2 null mutant indicate a general function in cellular stress response; the mutant displayed poor growth on non-fermentative media at 37{degrees}C, and in oleate, it is more sensitive to heat and oxidative stress while its overexpression confers resistance to some of the tested stressors. Dmo2p topology and modeled structure suggested a functional redox role for the Cx2C motif sustained by site-directed mutagenesis of both cysteine residues. The respiratory deficiency of dmo2 mutants at 37{degrees}C led to a reduction in cytochrome c oxidase activity (COX) and the formation of bc1-COX supercomplexes; we also observed a rapid turnover of Cox2p, the subunit two of the cytochrome c oxidase complex that harbors the binuclear CuA center. Moreover, Dmo2p co-immunoprecipitated with Cox2p and components of CuA center maturation such as Sco1p and Sco2p; and finally, DMO2 overexpression can suppress cox23 respiratory deficiency, a mutant that has the mitochondrial copper homeostasis impaired. Overall, our data suggest that Dmo2p is required for Cox2p maturation, potentially by aiding proteins involved in copper transport and incorporation into Cox2p.

molecular biology↗