Mitochondrial ribosome

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Schematic structure of the mitochondrion

The mitochondrial ribosome , also mitoribosome , is the ribosome of the mitochondria in eukaryotes . It is used for protein biosynthesis of some mitochondrial proteins .

properties

Mitochondrial ribosomes, like their cytosolic counterparts, are ribonucleoproteins , but have a higher protein content in comparison. While the proportion of RNA in mitochondrial ribosomes is around 30%, it is 50 to 60% in cytosolic ribosomes of eukaryotes and 60 to 70% in bacterial ribosomes. They consist of two subunits, the larger mtLSU ( mitochondrial large subunit , 39 S ) and the smaller mtSSU ( mitochondrial small subunit , 28 S). Together they form the mitochondrial ribosome with 55 S. The connection between the two subunits is more flexible than with other ribosomes, which enables more conformations .

The small subunit contains 30 proteins, the large subunit 50. The RNA of the small subunit consists of about 955 ribonucleotides (12 S) and the large subunit of about 1571 ribonucleotides (16 S). A tRNA is also bound. The mammalian mitochondrial ribosome contains 82 proteins, 39 of which have no homologues in other ribosomes. About 25% of the mitochondrial ribosomal proteins are used by the mitochondrial ribosome to compensate for the RNA, which is significantly shorter than that of the ribosome of bacteria, and almost all of its proteins are elongated compared to their bacterial homologues. Not all of the compensating additional proteins are located at the point where the RNA is shortened.

Mitochondrial translation

While more than 1500 proteins occur in the mitochondrion in humans (around 1000 in yeast ), only 13 proteins are encoded in the mtDNA (8 in yeast), while the remaining proteins are imported via signal sequences from the cytosol via Tom and Tim or from ribosomes in the cytosol connected to the outer mitochondrial membrane. All mitochondrially encoded proteins are proteins of the electron transport chain in oxidative phosphorylation . Four of the five protein complexes from it (I, III, IV, V) have proteins produced both cytosolically and mitochondrially.

In contrast to mRNA on cytosolic ribosomes, the mRNA in the mitochondrion, from which proteins are produced on mitochondrial ribosomes, does not contain a Shine-Dalgarno sequence or a cap structure . The mechanism by which translation is initiated on the mitochondrial ribosome is unknown.

Genetic defects

Defects in the mitochondrial ribosome can lead to various diseases, e.g. B. Leigh syndrome , sensorineural hearing loss , encephalomyopathy, and hypertrophic cardiomyopathy .

Individual evidence

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  7. ↑ MR Sharma, EC Koc, PP Datta, TM Booth, LL Spremulli, RK Agrawal: Structure of the mammalian mitochondrial ribosome reveals an expanded functional role for its component proteins. In: Cell. Volume 115, Number 1, October 2003, pp. 97-108, PMID 14532006 .
  8. ↑ C. Lesnik, A. Golani-Armon, Y. Arava: Localized translation near the mitochondrial outer membrane: An update. In: RNA biology. Volume 12, number 8, 2015, pp. 801-809, doi : 10.1080 / 15476286.2015.1058686 , PMID 26151724 , PMC 4615199 (free full text).
  9. ↑ H. Fraga, S. Ventura: Influence of Cytoplasmatic Folding on Mitochondrial Import. In: Current medicinal chemistry. Volume 22, Number 19, 2015, pp. 2349-2359, PMID 25760085 .
  10. ↑ LS Wenz, .. Opaliński, N. Wiedemann, T. Be: Cooperation of protein machineries in mitochondrial protein sorting. In: Biochimica et Biophysica Acta . Volume 1853, number 5, May 2015, pp. 1119–1129, doi : 10.1016 / j.bbamcr.2015.01.012 , PMID 25633533 .
  11. ^ Iain G. Johnston, Ben P. Williams: Evolutionary Inference across Eukaryotes Identifies Specific Pressures Favoring Mitochondrial Gene Retention . In: Cell Systems . 2, 2016, ISSN  2405-4712 , pp. 101-111. doi : 10.1016 / j.cels.2016.01.013 .
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