Exosome (protein complex)
| Parent |
| cell |
| Subordinate |
| Degradosome |
| Gene Ontology |
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| QuickGO |
The exosome (also PM / Scl complex ) is a protein complex that plays a role in the breakdown of ribonucleic acids (RNA). In the core of the exosome there are among other things six proteins arranged in a characteristic ring . The exosome is a very widespread and evolutionarily old protein complex in living nature. It occurs both in archaea and in the cells of the eukaryotes . In eukaryotic cells, the protein complex can be found in the cytoplasm as well as in the cell nucleus and is essential for the growth of these cells. In bacteria , its function is taken over by the degradosome .
construction
The nucleus of the exosome of the eukaryotes and archaea, like the structurally related polynucleotide phosphorylases (PNPases) of the bacterial degradosome, consists of six ring-shaped core proteins, three cap proteins and a central pore. Often these core-forming proteins occur in complex with additional proteins.
All six core proteins are ribonucleases (RNases) of the ribonuclease PH family. While the nucleus of the archaea exosome consists of only two different ribonucleases (three molecules each, Rrp41 and Rrp42 ), the nucleus of the eukaryotic exosome is built up by six different ribonucleases (Rrp41, Rrp45 , Rrp42, Rrp43 , Mtr3 and Rrp46 ). The eukaryotic proteins Rrp41, Mtr3 and Rrp46 find their respective counterparts in the Rrp41 of the archaea and the eukaryotic proteins Rrp45, Rrp42 and Rrp43 in the Rrp42 of the archaea.
The Cap proteins lying directly on the six core ribonucleases have an S1 RNA binding domain. In archaea, the cap proteins are represented by two molecules Rrp4 and one molecule Csl4 . The cap proteins of the eukaryotes consist of three different molecules (Rrp4, Rrp40 and Csl4). Both Rrp4 and Rrp40 of the eukaryotes correspond to the Rrp4 of the archaea.
The most common two eukaryotic proteins that appear in close association with the core and cap proteins that make up the nucleus are Rrp44 and Rrp6 . While Rrp44 is a ribonuclease of the RNase-R family, Rrp6 belongs to the ribonuclease family D. In addition, the components of the exosome protein complex can interact with numerous regulatory proteins.
function
The exosome is an enzyme complex involved in the cleavage of ribonucleic acids. Depending on the cell compartment and the regulatory proteins involved, messenger RNA (mRNA), ribosomal RNA (rRNA) or small RNAs are used as substrates . In the cytosol , the exosome is particularly involved in the breakdown of messenger RNA. The enzyme complex comes into contact with proteins, among other things, which recognize specific patterns (so-called AU-rich elements) in the 3'- untranslated area of the messenger RNA. In the cell nucleus , the exosome protein complex is required for the correct processing of small RNAs. In the nucleolus , the cell nucleus area with the highest exosome density, the enzyme complex also plays a central role in the processing of ribosomal RNA.
The functions of the exosome enzyme complex are based on its ribonuclease activity. The exosome has an exoribonuclease function , whereby the substrate can be broken down from the 3 'end of a ribonucleic acid strand. In contrast to the archaea exosome, the eukaryotic exosome has an additional endoribonuclease function , which allows splitting within a ribonucleic acid strand. While the exoribonuclease function of the archaea exosome is taken over by the ring-shaped core proteins Rrp41 and Rrp42, the exosome-associated proteins Rrp6 and Rrp44 are responsible for the RNA-cleaving function of the exosome of eukaryotes.
Although eukaryotes have other RNA-degrading enzymes at their disposal, the exosome is essential for cell survival. An experimental inhibition of the exosome function, for example with the help of RNA interference , leads to a stop of cell growth or to cell death .
literature
- Schilders G, van Dijk E, Raijmakers R, Pruijn GJ: Cell and molecular biology of the exosome: how to make or break an RNA . In: Int. Rev. Cytol. . 251, 2006, pp. 159-208. doi : 10.1016 / S0074-7696 (06) 51005-8 . PMID 16939780 .
- Torben Heick Jensen (Ed.): RNA Exosome . Springer, 2010, ISBN 1441978402 .
Individual evidence
- ^ A b Lorentzen E, Walter P, Friborg S, Evguenieva-Hackenberg E, Klug G, Conti E: The archaeal exosome core is a hexameric ring structure with three catalytic subunits . In: Nat. Struct. Mol. Biol . 12, No. 7, July 2005, pp. 575-81. doi : 10.1038 / nsmb952 . PMID 15951817 .
- ↑ a b Lin-Chao S, Chiou NT, Schuster G: The PNPase, exosome and RNA helicases as the building components of evolutionarily-conserved RNA degradation machines . In: Journal of Biomedical Science . 14, No. 4, 2007, pp. 523-32. doi : 10.1007 / s11373-007-9178-y . PMID 17514363 .
- ↑ Chen CY, Gherzi R, Ong SE, et al. : AU binding proteins recruit the exosome to degrade ARE-containing mRNAs . In: Cell . 107, No. 4, November 2001, pp. 451-64. PMID 11719186 .
- ↑ Allmang C, Kufel J, Chanfreau G, Mitchell P, Petfalski E, Tollervey D: Functions of the exosome in rRNA, snoRNA and snRNA synthesis . In: EMBO J. . 18, No. 19, October 1999, pp. 5399-410. doi : 10.1093 / emboj / 18.19.5399 . PMID 10508172 . PMC 1171609 (free full text).
- ↑ Schilders G, Raijmakers R, Raats JM, Pruijn GJ: MPP6 is an exosome-associated RNA-binding protein involved in 5.8S rRNA maturation . In: Nucleic Acids Res . 33, No. 21, 2005, pp. 6795-804. doi : 10.1093 / nar / gki982 . PMID 16396833 . PMC 1310903 (free full text).