bims-mitran 2023-09-03 papers

Issue of 2023–09–03
three papers selected by
Andreas Kohler, University of Graz

Science. 2023 Sep;381(6661): eadg0995

An mTRAN-mRNA interaction mediates mitochondrial translation initiation in plants.

Huy Cuong Tran, Vivian Schmitt, Sbatie Lama, Chuande Wang, Alexandra Launay-Avon, Katja Bernfur, Kristin Sultan, Kasim Khan, Véronique Brunaud, Arnaud Liehrmann, Benoît Castandet, Fredrik Levander, Allan G Rasmusson, Hakim Mireau, Etienne Delannoy, Olivier Van Aken.

Plant mitochondria represent the largest group of respiring organelles on the planet. Plant mitochondrial messenger RNAs (mRNAs) lack Shine-Dalgarno-like ribosome-binding sites, so it is unknown how plant mitoribosomes recognize mRNA. We show that "mitochondrial translation factors" mTRAN1 and mTRAN2 are land plant-specific proteins, required for normal mitochondrial respiration chain biogenesis. Our studies suggest that mTRANs are noncanonical pentatricopeptide repeat (PPR)-like RNA binding proteins of the mitoribosomal "small" subunit. We identified conserved Adenosine (A)/Uridine (U)-rich motifs in the 5' regions of plant mitochondrial mRNAs. mTRAN1 binds this motif, suggesting that it is a mitoribosome homing factor to identify mRNAs. We demonstrate that mTRANs are likely required for translation of all plant mitochondrial mRNAs. Plant mitochondrial translation initiation thus appears to use a protein-mRNA interaction that is divergent from bacteria or mammalian mitochondria.

DOI: https://doi.org/10.1126/science.adg0995

Mol Microbiol. 2023 Aug 30.

SUMOylation of yeast Pso2 enhances its translocation and accumulation in the mitochondria and suppresses methyl methanesulfonate-induced mitochondrial DNA damage.

Shravanahalli C Somashekara, Kshitiza M Dhyani, Manoj Thakur, Kalappa Muniyappa.

Saccharomyces cerevisiae Pso2/SNM1 is essential for DNA interstrand crosslink (ICL) repair; however, its mechanism of action remains incompletely understood. While recent work has revealed that Pso2/Snm1 is dual-localized in the nucleus and mitochondria, it remains unclear whether cell-intrinsic and -extrinsic factors regulate its subcellular localization and function. Herein, we show that Pso2 undergoes ubiquitination and phosphorylation, but not SUMOylation, in unstressed cells. Unexpectedly, we found that methyl methanesulfonate (MMS), rather than ICL-forming agents, induced robust SUMOylation of Pso2 on two conserved residues, K97 and K575, and that SUMOylation markedly increased its abundance in the mitochondria. Reciprocally, SUMOylation had no discernible impact on Pso2 translocation to the nucleus, despite the presence of steady-state levels of SUMOylated Pso2 across the cell cycle. Furthermore, substitution of the invariant residues K97 and K575 by arginine in the Pso2 SUMO consensus motifs severely impaired SUMOylation and abolished its translocation to the mitochondria of MMS-treated wild type cells, but not in unstressed cells. We demonstrate that whilst Siz1 and Siz2 SUMO E3 ligases catalyze Pso2 SUMOylation, the former plays a dominant role. Notably, we found that the phenotypic characteristics of the SUMOylation-defective mutant Pso2K97R/K575R closely mirrored those observed in the Pso2Δ petite mutant. Additionally, leveraging next-generation sequencing analysis, we demonstrate that Pso2 mitigates MMS-induced damage to mitochondrial DNA (mtDNA). Viewed together, our work offers previously unknown insights into the link between genotoxic stress-induced SUMOylation of Pso2 and its preferential targeting to the mitochondria, as well as its role in attenuating MMS-induced mtDNA damage.

Keywords: ICL repair; Pso2; SUMOylation; mitochondrial localization; mtDNA repair

DOI: https://doi.org/10.1111/mmi.15145

Am J Physiol Cell Physiol. 2023 Aug 29.

Mitochondrial Microproteins: Critical Regulators of Protein Import, Energy Production, Stress Response Pathways, and Programmed Cell Death.

Michael L Kamradt, Catherine A Makarewich.

Mitochondria rely upon the coordination of protein import, protein translation, and proper functioning of oxidative phosphorylation (OXPHOS) complexes I-V to sustain the activities of life for an organism. Each process is dependent upon the function of profoundly large protein complexes found in the mitochondria (TOMM complex, TIMM complex, OXPHOS complexes, mitoribosomes). These massive protein complexes, in some instances more than one megadalton, are built up from numerous protein subunits of varying sizes, including many proteins that are ≤100-150 amino acids. However, these small proteins, termed microproteins, not only act as cogs in large molecular machines; they also have important steps in inhibiting or promoting the intrinsic pathway of apoptosis, coordinate responses to cellular stress and even act as hormones. This review focuses on microproteins that occupy the mitochondria and are critical for its function. Although the microprotein field is relatively new, researchers have long recognized the existence of these mitochondrial proteins as critical components of virtually all aspects of mitochondrial biology. Thus, recent studies estimating that hundreds of new microproteins of unknown function exist and are missing from current genome annotations suggests that the mitochondrial "microproteome" is a rich area for future biological investigation.

Keywords: cell stress; microproteins; mitochondria; mitochondrial protein import; oxidative phosphorylation

DOI: https://doi.org/10.1152/ajpcell.00189.2023