bims-mitran 2023-12-24 papers

Issue of 2023–12–24
four papers selected by
Andreas Kohler, Umeå University

IUBMB Life. 2023 Dec 20.

Schizosaccharomyces pombe as a fundamental model for research on mitochondrial gene expression: Progress, achievements and outlooks.

Nhu Dinh, Nathalie Bonnefoy.

Schizosaccharomyces pombe (fission yeast) is an attractive model for mitochondrial research. The organism resembles human cells in terms of mitochondrial inheritance, mitochondrial transport, sugar metabolism, mitogenome structure and dependence of viability on the mitogenome (the petite-negative phenotype). Transcriptions of these genomes produce only a few polycistronic transcripts, which then undergo processing as per the tRNA punctuation model. In general, the machinery for mitochondrial gene expression is structurally and functionally conserved between fission yeast and humans. Furthermore, molecular research on S. pombe is supported by a considerable number of experimental techniques and database resources. Owing to these advantages, fission yeast has significantly contributed to biomedical and fundamental research. Here, we review the current state of knowledge regarding S. pombe mitochondrial gene expression, and emphasise the pertinence of fission yeast as both a model and tool, especially for studies on mitochondrial translation.

Keywords: OXPHOS complexes; PPR proteins; Schizosaccharomyces pombe; gene expression; gene fusions; mitochondrial biogenesis; mitoribosome

DOI: https://doi.org/10.1002/iub.2801

Biochemistry (Mosc). 2023 Nov;88(11): 1832-1843

Diversity and Evolution of Mitochondrial Translation Apparatus.

Mariya V Baleva, Ulyana E Piunova, Ivan V Chicherin, Sergey A Levitskii, Piotr A Kamenski.

The evolution of mitochondria has proceeded independently in different eukaryotic lines, which is reflected in the diversity of mitochondrial genomes and mechanisms of their expression in eukaryotic species. Mitochondria have lost most of bacterial ancestor genes by transferring them to the nucleus or eliminating them. However, mitochondria of almost all eukaryotic cells still retain relatively small genomes, as well as their replication, transcription, and translation apparatuses. The dependence on the nuclear genome, specific features of mitochondrial transcripts, and synthesis of highly hydrophobic membrane proteins in the mitochondria have led to significant changes in the translation apparatus inherited from the bacterial ancestor, which retained the basic structure necessary for protein synthesis but became more specialized and labile. In this review, we discuss specific properties of translation initiation in the mitochondria and how the evolution of mitochondria affected the functions of main factors initiating protein biosynthesis in these organelles.

Keywords: mitochondria; regulation of translation; translation; translation initiation factors

DOI: https://doi.org/10.1134/S0006297923110135

Int J Mol Sci. 2023 Dec 15. pii: 17503. [Epub ahead of print]24(24):

Translation Fidelity and Respiration Deficits in CLPP-Deficient Tissues: Mechanistic Insights from Mitochondrial Complexome Profiling.

Jana Key, Suzana Gispert, Gabriele Koepf, Julia Steinhoff-Wagner, Marina Reichlmeir, Georg Auburger.

The mitochondrial matrix peptidase CLPP is crucial during cell stress. Its loss causes Perrault syndrome type 3 (PRLTS3) with infertility, neurodegeneration, and a growth deficit. Its target proteins are disaggregated by CLPX, which also regulates heme biosynthesis via unfolding ALAS enzymes, providing access for pyridoxal-5'-phosphate (PLP). Despite efforts in diverse organisms with multiple techniques, CLPXP substrates remain controversial. Here, avoiding recombinant overexpression, we employed complexomics in mitochondria from three mouse tissues to identify endogenous targets. A CLPP absence caused the accumulation and dispersion of CLPX-VWA8 as AAA+ unfoldases, and of PLPBP. Similar changes and CLPX-VWA8 co-migration were evident for mitoribosomal central protuberance clusters, translation factors like GFM1-HARS2, the RNA granule components LRPPRC-SLIRP, and enzymes OAT-ALDH18A1. Mitochondrially translated proteins in testes showed reductions to <30% for MTCO1-3, the mis-assembly of the complex IV supercomplex, and accumulated metal-binding assembly factors COX15-SFXN4. Indeed, heavy metal levels were increased for iron, molybdenum, cobalt, and manganese. RT-qPCR showed compensatory downregulation only for Clpx mRNA; most accumulated proteins appeared transcriptionally upregulated. Immunoblots validated VWA8, MRPL38, MRPL18, GFM1, and OAT accumulation. Co-immunoprecipitation confirmed CLPX binding to MRPL38, GFM1, and OAT, so excess CLPX and PLP may affect their activity. Our data mechanistically elucidate the mitochondrial translation fidelity deficits which underlie progressive hearing impairment in PRLTS3.

Keywords: azoospermia; mtLSU quality control; primary ovarian insufficiency; rRNA chaperone ERAL1; sensorineural hearing loss

DOI: https://doi.org/10.3390/ijms242417503

Nucleic Acids Res. 2023 Dec 19. pii: gkad1197. [Epub ahead of print]

Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP).

Raja Norazireen Raja Ahmad, Long-Teng Zhang, Rikuri Morita, Haruna Tani, Yong Wu, Takeshi Chujo, Akiko Ogawa, Ryuhei Harada, Yasuteru Shigeta, Kazuhito Tomizawa, Fan-Yan Wei.

MTU1 controls intramitochondrial protein synthesis by catalyzing the 2-thiouridine modification of mitochondrial transfer RNAs (mt-tRNAs). Missense mutations in the MTU1 gene are associated with life-threatening reversible infantile hepatic failure. However, the molecular pathogenesis is not well understood. Here, we investigated 17 mutations associated with this disease, and our results showed that most disease-related mutations are partial loss-of-function mutations, with three mutations being particularly severe. Mutant MTU1 is rapidly degraded by mitochondrial caseinolytic peptidase (CLPP) through a direct interaction with its chaperone protein CLPX. Notably, knockdown of CLPP significantly increased mutant MTU1 protein expression and mt-tRNA 2-thiolation, suggesting that accelerated proteolysis of mutant MTU1 plays a role in disease pathogenesis. In addition, molecular dynamics simulations demonstrated that disease-associated mutations may lead to abnormal intermolecular interactions, thereby impairing MTU1 enzyme activity. Finally, clinical data analysis underscores a significant correlation between patient prognosis and residual 2-thiolation levels, which is partially consistent with the AlphaMissense predictions. These findings provide a comprehensive understanding of MTU1-related diseases, offering prospects for modification-based diagnostics and novel therapeutic strategies centered on targeting CLPP.

DOI: https://doi.org/10.1093/nar/gkad1197