80S核糖体
80S核糖体（英语：80S ribosomes）又称真核核糖体（英语：Eukaryotic ribosomes），是真核生物细胞质中的核糖体，得名自其沉降系数，由40S小次单元与60S大次单元组成，成分为蛋白质与RNA，为真核细胞中合成蛋白质（转译）的场所。80S核糖体比原核生物的70S核糖体还大，组装与调控机制也比后者更加复杂[1][2]。
结构 编辑
80S核糖体的结构最早是用电子显微镜测得，分辨率为30–40 Å[3][4]，低温电子显微镜问世后得以观测蛋白与RNA片段等更精密的结构[5]。80S核糖体大于原核生物的70S核糖体，其中许多核糖体蛋白比原核生物的同源蛋白多了些延伸片段，也有些核糖体蛋白为真核生物独有，不见于原核生物中。40S小次单元中含有18S rRNA（和原核生物的16S rRNA同源）；60S小次单元中有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（特别是18S与28S）上比原核生物的多了许多扩张片段（expansion segments）[8]。
真核生物特有的核糖体蛋白包括40S的RPS7、RPS10、RPS12与RACK1，以及60S的RPL6、RPL22、RPL27、RPL28、RPL29与RPL36等，这些蛋白与其他核糖体蛋白中真核生物特有的延伸片段多位于核糖体表面，其中许多与rRNA扩张片段互动[9][10]。相较于原核生物30S的喙（beak）皆是由rRNA构成，真核生物40S的RPS10与RPS12为形成喙结构的重要蛋白[9]。
80S核糖体中有两个核糖体蛋白（RPS27A和RPL40）为泛素融合蛋白，需先由蛋白酶将其N端的泛素切除才能组装成正常核糖体[9][10][11]。另外有两个核糖体蛋白（RPS6与RACK1）参与细胞中的讯息传递途径，前者可被mTOR磷酸化而调控转译[12]，后者除调控转译外还参与许多其他反应途径[13]。
比较 编辑
| 真核生物[14] | 细菌[14] | ||
|---|---|---|---|
| 核糖体 | 沈降系数 | 80S | 70S |
| 分子量 | ~3.2×106 Da | ~2.0×106 Da | |
| 大小 | ~250–300 Å | ~200 Å | |
| 大次单元 | 沈降系数 | 60S | 50S |
| 分子量 | ~2.0×106 Da | ~1.3×106 Da | |
| 蛋白质 | 46个 | 33个 | |
| rRNA |
|
| |
| 小次单元 | 沈降系数 | 40S | 30S |
| 分子量 | ~1.2×106 Da | ~0.7×106 Da | |
| 蛋白质 | 33个 | 20个 | |
| rRNA |
|
|
参考文献 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 数值分别来自四膜虫核糖体（PDB：4V8P）与嗜热栖热菌核糖体（PDB：4V5D），具体大小、分子量蛋白数目可能因物种而略有差异。
