80S核糖体
80S核糖體（英語：80S ribosomes）又稱真核核糖體（英語：Eukaryotic ribosomes），是真核生物細胞質中的核糖體，得名自其沉降系数，由40S小次單元與60S大次單元組成，成分為蛋白質與RNA，為真核細胞中合成蛋白質（轉譯）的場所。80S核糖體比原核生物的70S核糖體還大，組裝與調控機制也比後者更加複雜[1][2]。
結構
[编辑]80S核糖體的結構最早是用電子顯微鏡測得，解析度為30–40 Å[3][4]，低溫電子顯微鏡問世後得以觀測蛋白與RNA片段等更精密的結構[5]。80S核糖體大於原核生物的70S核糖體，其中許多核糖體蛋白比原核生物的同源蛋白多了些延伸片段，也有些核糖體蛋白為真核生物獨有，不見於原核生物中。40S小次單元中含有18S rRNA（和原核生物的16S rRNA同源）；60S小次單元中有28S rRNA（和原核生物的23S rRNA同源）、5.8S rRNA（和原核生物23S rRNA末端的序列同源）以及5S rRNA（三域生物皆有）[6][7]，真核生物的rRNA（特別是18S與28S）上比原核生物的多了許多擴張片段（expansion segments）[8]。
真核生物特有的核糖體蛋白包括40S的RPS7、RPS10、RPS12與RACK1，以及60S的RPL6、RPL22、RPL27、RPL28、RPL29與RPL36等，這些蛋白與其他核糖體蛋白中真核生物特有的延伸片段多位於核糖體表面，其中許多與rRNA擴張片段互動[9][10]。相較於原核生物30S的喙（beak）皆是由rRNA構成，真核生物40S的RPS10與RPS12為形成喙結構的重要蛋白[9]。
80S核糖體中有兩個核糖體蛋白（RPS27A和RPL40）為泛素融合蛋白，需先由蛋白酶將其N端的泛素切除才能組裝成正常核糖體[9][10][11]。另外有兩個核糖體蛋白（RPS6與RACK1）參與細胞中的訊息傳遞途徑，前者可被mTOR磷酸化而調控轉譯[12]，後者除調控轉譯外還參與許多其他反應途徑[13]。
比較
[编辑]| 真核生物[14] | 細菌[14] | ||
|---|---|---|---|
| 核糖體 | 沈降係數 | 80S | 70S |
| 分子量 | ~3.2×106 Da | ~2.0×106 Da | |
| 大小 | ~250–300 Å | ~200 Å | |
| 大次單元 | 沈降係數 | 60S | 50S |
| 分子量 | ~2.0×106 Da | ~1.3×106 Da | |
| 蛋白質 | 46個 | 33個 | |
| rRNA |
|
| |
| 小次單元 | 沈降係數 | 40S | 30S |
| 分子量 | ~1.2×106 Da | ~0.7×106 Da | |
| 蛋白質 | 33個 | 20個 | |
| rRNA |
|
|
參考文獻
[编辑]
- ^ Difference Between 70S Ribosomes and 80S Ribosomes, RNA, Micromolecules. www.microbiologyprocedure.com. [2009-08-06]. （原始内容存档于2008-09-05）.
- ^ 80S Ribosomes, Eukaryotic Ribosomes, Prokaryotic Ribosomes, Nucleic Acids, Sedimentation Coefficient. www.microbiologyprocedure.com. [2009-08-06]. （原始内容存档于2009-06-23）.
- ^ Verschoor, A; Warner, JR; Srivastava, S; Grassucci, RA; Frank, J. Three-dimensional structure of the yeast ribosome. Nucleic Acids Res. Jan 1998, 26 (2): 655–661. PMC 147289
. PMID 9421530. doi:10.1093/nar/26.2.655.
- ^ Verschoor, A; Frank, J. Three-dimensional structure of the mammalian cytoplasmic ribosome. J Mol Biol. Aug 1990, 214 (3): 737–749. PMID 2388265. doi:10.1016/0022-2836(90)90289-X.
- ^ Spahn, CM; Beckmann, R; Eswar, N; Penczek, PA; Sali, A; Blobel, G; Frank, J. Structure of the 80S ribosome from Saccharomyces cerevisiae--tRNA-ribosome and subunit-subunit interactions.. Cell. Nov 2001, 107 (3): 373–386. PMID 11701127. doi:10.1016/s0092-8674(01)00539-6.
- ^ Alberts, Bruce; et al. The Molecular Biology of the Cell 4th. Garland Science. 2002: 342. ISBN 978-0-8153-3218-3.
- ^ Ben-Shem A, Garreau de Loubresse N, Melnikov S, Jenner L, Yusupova G, Yusupov M. The structure of the eukaryotic ribosome at 3.0 Å resolution. Science. December 2011, 334 (6062): 1524–9. Bibcode:2011Sci...334.1524B. PMID 22096102. doi:10.1126/science.1212642.
- ^ Ramesh M, Woolford JL. Eukaryote-specific rRNA expansion segments function in ribosome biogenesis.. RNA. 2016, 22 (8): 1153–62. PMC 4931108 . PMID 27317789. doi:10.1261/rna.056705.116.
- ^ 9.0 9.1 9.2 Rabl, J; Leibundgut, M; Ataide, SF; Haag, A; Ban, N. Crystal structure of the eukaryotic 40S ribosomal subunit in complex with initiation factor 1. Science. Feb 2011, 331 (6018): 730–736. PMID 21205638. doi:10.1126/science.1198308. hdl:20.500.11850/153130.
- ^ 10.0 10.1 Klinge, S; Voigts-Hoffmann, F; Leibundgut, M; Arpagaus, S; Ban, N. Crystal structure of the eukaryotic 60S ribosomal subunit in complex with initiation factor 6. Science. Nov 2011, 334 (6058): 941–948. PMID 22052974. doi:10.1126/science.1211204.
- ^ Lacombe, T; García-Gómez, JJ; de la Cruz, J; Roser, D; Hurt, E; Linder, P; Kressler, D. Linear ubiquitin fusion to Rps31 and its subsequent cleavage are required for the efficient production and functional integrity of 40S ribosomal subunits. Mol Microbiol. Apr 2009, 72 (1): 69–84. PMID 19210616. doi:10.1111/j.1365-2958.2009.06622.x.
- ^ Palm, L; Andersen, J; Rahbek-Nielsen, H; Hansen, TS; Kristiansen, K; Højrup, P. The phosphorylated ribosomal protein S7 in Tetrahymena is homologous with mammalian S4 and the phosphorylated residues are located in the C-terminal region. Structural characterization of proteins separated by two-dimensional polyacrylamide gel electrophoresis.. J Biol Chem. Mar 1995, 270 (11): 6000–6005. PMID 7890730. doi:10.1074/jbc.270.11.6000.
- ^ Nilsson, J; Sengupta, J; Frank, J; Nissen, P. Regulation of eukaryotic translation by the RACK1 protein: a platform for signalling molecules on the ribosome. EMBO Rep. Dec 2004, 5 (12): 1137–1141. PMC 1299186 . PMID 15577927. doi:10.1038/sj.embor.7400291.
- ^ 14.0 14.1 數值分別來自四膜蟲核糖體（PDB：4V8P）與嗜熱棲熱菌核糖體（PDB：4V5D），具體大小、分子量蛋白數目可能因物種而略有差異。