| 1. |
- Gruschke, Steffi, et al.
(författare)
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Cbp3-Cbp6 interacts with the yeast mitochondrial ribosomal tunnel exit and promotes cytochrome b synthesis and assembly
- 2011
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Ingår i: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 193:6, s. 1101-1114
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondria contain their own genetic system to express a small number of hydrophobic polypeptides, including cytochrome b, an essential subunit of the bc(1) complex of the respiratory chain. In this paper, we show in yeast that Cbp3, a bc(1) complex assembly factor, and Cbp6, a regulator of cytochrome b translation, form a complex that associates with the polypeptide tunnel exit of mitochondrial ribosomes and that exhibits two important functions in the biogenesis of cytochrome b. On the one hand, the interaction of Cbp3 and Cbp6 with mitochondrial ribosomes is necessary for efficient translation of cytochrome b messenger ribonucleic acid or transcript. On the other hand, the Cbp3-Cbp6 complex interacts directly with newly synthesized cytochrome b in an assembly intermediate that is not ribosome bound and that contains the assembly factor Cbp4. Our results suggest that synthesis of cytochrome b occurs preferentially on those ribosomes that have the Cbp3-Cbp6 complex bound to their tunnel exit, an arrangement that may ensure tight coordination of cytochrome b synthesis and assembly.
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| 2. |
- Gruschke, Steffi, et al.
(författare)
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Proteins at the Polypeptide Tunnel Exit of the Yeast Mitochondrial Ribosome
- 2010
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 285:25, s. 19022-19028
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Tidskriftsartikel (refereegranskat)abstract
- Oxidative phosphorylation in mitochondria requires the synthesis of proteins encoded in the mitochondrial DNA. The mitochondrial translation machinery differs significantly from that of the bacterial ancestor of the organelle. This is especially evident from many mitochondria-specific ribosomal proteins. An important site of the ribosome is the polypeptide tunnel exit. Here, nascent chains are exposed to an aqueous environment for the first time. Many biogenesis factors interact with the tunnel exit of pro- and eukaryotic ribosomes to help the newly synthesized proteins to mature. To date, nothing is known about the organization of the tunnel exit of mitochondrial ribosomes. We therefore undertook a comprehensive approach to determine the composition of the yeast mitochondrial ribosomal tunnel exit. Mitochondria contain homologues of the ribosomal proteins located at this site in bacterial ribosomes. Here, we identified proteins located in their proximity by chemical cross-linking and mass spectrometry. Our analysis revealed a complex network of interacting proteins including proteins and protein domains specific to mitochondrial ribosomes. This network includes Mba1, the membrane-bound ribosome receptor of the inner membrane, as well as Mrpl3, Mrpl13, and Mrpl27, which constitute ribosomal proteins exclusively found in mitochondria. This unique architecture of the tunnel exit is presumably an adaptation of the translation system to the specific requirements of the organelle.
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| 3. |
- Heublein, Manfred, et al.
(författare)
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The novel component Kgd4 recruits the E3 subunit to the mitochondrial alpha-ketoglutarate dehydrogenase
- 2014
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Ingår i: Molecular Biology of the Cell. - 1059-1524 .- 1939-4586. ; 25:21, s. 3342-3349
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Tidskriftsartikel (refereegranskat)abstract
- The mitochondrial citric acid cycle is a central hub of cellular metabolism, providing intermediates for biosynthetic pathways and channeling electrons to the respiratory chain complexes. In this study, we elucidated the composition and organization of the multienzyme complex alpha-ketoglutarate dehydrogenase (alpha-KGDH). In addition to the three classical E1-E3 subunits, we identified a novel component, Kgd4 (Ymr31/MRPS36), which was previously assigned to be a subunit of the mitochondrial ribosome. Biochemical analyses demonstrate that this protein plays an evolutionarily conserved role in the organization of mitochondrial alpha-KGDH complexes of fungi and animals. By binding to both the E1-E2 core and the E3 subunit, Kgd4 acts as a molecular adaptor that is necessary to a form a stable alpha-KGDH enzyme complex. Our work thus reveals a novel subunit of a key citric acid-cycle enzyme and shows how this large complex is organized.
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