Structure of the Escherichia coli ribosomal termination complex with release factor 2
Structure of the Escherichia coli ribosomal termination complex with release factor 2
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DOI：
10.1038/nature01225
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发表时间：
2003-01-02
期刊：
影响因子：
64.8
通讯作者：
van Heel, M
中科院分区：
文献类型：
--
作者：
Klaholz, BP;Pape, T;van Heel, M
蛋白质合成的终止（1）发生在信使RNA在核糖体氨酰基（A）位点出现终止密码子时。据信I类释放因子蛋白（RF 1或RF 2）通过三肽基序识别终止密码子（2），导致完整的多肽链从其与核糖体肽基（P）位点的转移RNA的共价连接中释放。I类RF具有保守的GGQ氨基酸基序，被认为直接参与蛋白质-转移-RNA键水解（3，4）。已经确定了细菌和真核I类RF的晶体结构（5，6），但终止密码子识别和肽基-tRNA水解的机制仍不清楚。在这里，我们提出了结构的大肠杆菌核糖体在终止后复合物RF 2，通过单粒子冷冻电子显微镜（cryo-EM）。将已知的70 S和RF 2结构拟合到电子密度图中揭示了RF 2在核糖体上采用了与分离蛋白质的晶体结构相比不同的构象。RF 2的氨基末端螺旋结构域接触核糖体的因子结合位点，蛋白质的“SPF”环靠近mRNA，RF 2的含GGQ结构域与肽基转移酶中心（PTC）相互作用。通过连接核糖体解码中心与PTC，RF 2在功能上模拟A位点的tRNA分子。真核生物中的翻译终止可能基于类似的机制。
Termination of protein synthesis(1) occurs when the messenger RNA presents a stop codon in the ribosomal aminoacyl (A) site. Class I release factor proteins (RF1 or RF2) are believed to recognize stop codons via tripeptide motifs(2), leading to release of the completed polypeptide chain from its covalent attachment to transfer RNA in the ribosomal peptidyl (P) site. Class I RFs possess a conserved GGQ amino-acid motif that is thought to be involved directly in protein-transfer-RNA bond hydrolysis(3,4). Crystal structures of bacterial and eukaryotic class I RFs have been determined(5,6), but the mechanism of stop codon recognition and peptidyl-tRNA hydrolysis remains unclear. Here we present the structure of the Escherichia coli ribosome in a post-termination complex with RF2, obtained by single-particle cryo-electron microscopy (cryo-EM). Fitting the known 70S and RF2 structures into the electron density map reveals that RF2 adopts a different conformation on the ribosome when compared with the crystal structure of the isolated protein. The amino-terminal helical domain of RF2 contacts the factor-binding site of the ribosome, the 'SPF' loop of the protein is situated close to the mRNA, and the GGQ-containing domain of RF2 interacts with the peptidyl-transferase centre (PTC). By connecting the ribosomal decoding centre with the PTC, RF2 functionally mimics a tRNA molecule in the A site. Translational termination in eukaryotes is likely to be based on a similar mechanism.