bims-cytox1 2023-10-08 papers

Issue of 2023‒10‒08
two papers selected by
Gavin McStay, Liverpool John Moores University

Biochim Biophys Acta Mol Cell Res. 2023 Sep 26. pii: S0167-4889(23)00174-X. [Epub ahead of print]1871(1): 119601

Knockdown of BRAWNIN minimally affect mitochondrial complex III assembly in human cells.

Ya Wang, Yu Shi, Wen Li, Xinyu Han, Xi Lin, Dandan Liu, Yuyan Lin, Lijun Shen.

BRAWNIN was found as a mitochondrial respiratory complex III (CIII) assembly factor. Here, we showed that the deletion rather than knockdown of BRAWNIN impaired the assembly of CIII. BRAWNIN levels were affected by nutritional stress and negatively associated with AMPK activation. Although the BRAWNIN knockout via CRISPR/Cas9 led to decreased complex III levels, both biochemical and functional studies of oxidative phosphorylation system (OXPHOS) complexes revealed that knockdown of BRAWNIN neither affected mitochondrial respiration nor impaired the integrity of OXPHOS complexes I-V. Transcriptomic and proteomic profiling further confirmed that the BRAWNIN knockdown had a minimal effect on mitochondrial function. Moreover, only a small proportion of BRAWNIN interacted with the subunits of the OXPHOS complexes, which might be difficult to detect via co-immunoprecipitation and mass spectrometry. Finally, our findings also indicated that although only a minimal amount of BRAWNIN was required for CIII assembly, metabolic analyses revealed that it may fine-tune the pyruvate metabolism route in mitochondria.

DOI: https://doi.org/10.1016/j.bbamcr.2023.119601

Mol Biol Cell. 2023 Oct 04. mbcE23040132

Mutation of the PEBP-like domain of the mitoribosomal MrpL35/mL38 protein results in production of nascent chains with impaired capacity to assemble into OXPHOS complexes.

Jodie M Box, Jessica M Anderson, Rosemary A Stuart.

Located in the central protuberance region of the mitoribosome, mitospecific mL38 proteins display homology to PEBP (phosphatidylethanolamine binding protein) proteins, a diverse family of proteins reported to bind anionic substrates/ligands and implicated in cellular signaling and differentiation pathways. In this study, we have performed a mutational analysis of the yeast mitoribosomal protein MrpL35/mL38 and demonstrate that mutation of the PEBP-invariant ligand binding residues Asp(D)232 and Arg(R)288 impacted MrpL35/mL38's ability to support OXPHOS-based growth of the cell. Furthermore, our data indicate these residues exist in a functionally important charged microenvironment, which also includes Asp(D)167 of MrpL35/mL38 and Arg(R)127 of the neighboring Mrp7/bL27m protein. We report that mutation of each of these charged residues resulted in a strong reduction in OXPHOS complex levels that was not attributed to a corresponding inhibition of the mitochondrial translation process. Rather, our findings indicate that a disconnect exists in these mutants between the processes of mitochondrial protein translation and the events required to ensure the competency and/or availability of the newly synthesized proteins to assemble into OXPHOS enzymes. Based on our findings, we postulate that the PEBP-homology domain of MrpL35/mL38, together with its partner Mrp7/bL27m, form a key regulatory region of the mitoribosome.

DOI: https://doi.org/10.1091/mbc.E23-04-0132