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The ribosome receptors Mrx15 and Mba1 jointly organize cotranslational insertion and protein biogenesis in mitochondria
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2018 (English)In: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 29, no 20, p. 2359-2507Article in journal (Refereed) Published
Abstract [en]

Mitochondrial gene expression in Saccharomyces cerevisiae is responsible for the production of highly hydrophobic subunits of the oxidative phosphorylation system. Membrane insertion occurs cotranslationally on membrane-bound mitochondrial ribosomes. Here, by employing a systematic mass spectrometry-based approach, we discovered the previously uncharacterized membrane protein Mrx15 that interacts via a soluble C-terminal domain with the large ribosomal subunit. Mrx15 contacts mitochondrial translation products during their synthesis and plays, together with the ribosome receptor Mba1, an overlapping role in cotranslational protein insertion. Taken together, our data reveal how these ribosome receptors organize membrane protein biogenesis in mitochondria.

Place, publisher, year, edition, pages
2018. Vol. 29, no 20, p. 2359-2507
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-159308DOI: 10.1091/mbc.E18-04-0227ISI: 000451910900004OAI: oai:DiVA.org:su-159308DiVA, id: diva2:1241992
Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2019-01-07Bibliographically approved
In thesis
1. The interactome of the yeast mitochondrial ribosome: Organization of mitochondrial post-transcriptional regulation, membrane protein insertion and quality control
Open this publication in new window or tab >>The interactome of the yeast mitochondrial ribosome: Organization of mitochondrial post-transcriptional regulation, membrane protein insertion and quality control
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The proteins found in mitochondria originate from two different genetic systems. Most mitochondrial proteins are synthesized in the cytosol and post-translationally imported into the organelle. However, a small subset of mitochondrial proteins is encoded in an organelle-resident genome. Mitochondria contain factors responsible for replication, transcription and, most important for this thesis, synthesis of the mitochondrially encoded proteins. In the course of evolution the mitochondria specific ribosomes were extensively remodeled. The reasons for many of these adaptations are currently not well understood. For example, the mitoribosome is less stable and abundant than its bacterial counterpart. Therefore, I contributed in the development of robust biochemical tools in order to isolate and analyze the intact yeast mitoribosome and interaction partners by mass spectrometry. The results revealed a higher order organization of mitochondrial gene expression in complexes that we termed MIOREX (mitochondrial organization of gene expression). Besides the mitoribosome, MIOREX complexes contain factors involved in all steps of gene expression. This study also established many new ribosomal interaction partners, among them some proteins that were previously completely uncharacterized. In order to study these proteins, I refined the mass spectrometry approach, allowing a subunit-specific assignment of ribosomal interaction partners. The Mrx15 protein was determined by this approach as an interactor of the large subunit. I established that Mrx15 has overlapping functions with the ribosome receptor Mba1. Both proteins are necessary for mitoribosome membrane attachment and co-translational Cox2 membrane insertion. In a subsequent study I found a functional interaction of MRX15 and MBA1 with the regulators of the membrane-bound AAA proteases of the mitochondrial quality control system. Furthermore, the absence of Mrx15 leads to increased, the absence of Mba1 to decreased proteotoxic stress resistance of yeast cells. These results demonstrate an interesting connection between the mitochondrial quality control and membrane insertion machineries, suggesting an early quality control step during the biogenesis of mitochondrially encoded proteins. In addition, we could reveal a subunit-specific interaction of translational activators and client mRNAs with the mitochondrial ribosome. This organization demonstrated how cytochrome b synthesis is pre-organized by specific translational activators independently of the COB mRNA. In summary, the work in this thesis showed how the vast and diverse interactome of the yeast mitoribosome organizes and regulates mitochondrial translation. These regulation mechanisms highlighted many organelle specific features. The work presented here will serve as starting point to design future studies aimed at a better understanding on how mitochondria adapted to organize gene expression inside the organelle.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2018. p. 72
Keywords
Mitochondria, mitochondrial post-transcriptional regulation, mitochondrial ribosome, membrane protein insertion, mitochondrial quality control
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-159455 (URN)978-91-7797-404-8 (ISBN)978-91-7797-405-5 (ISBN)
Public defence
2018-10-19, Magnélisalen Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.

Available from: 2018-09-26 Created: 2018-09-05 Last updated: 2018-12-18Bibliographically approved

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