Ma Chengying, Wu Shan, Li Ningning, Chen Yan, Yan Kaige, Li Zhifei, Zheng Lvqin, Lei Jianlin, Woolford John L, Gao Ning
Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China.
Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
Nat Struct Mol Biol. 2017 Mar;24(3):214-220. doi: 10.1038/nsmb.3364. Epub 2017 Jan 23.
A key step in ribosome biogenesis is the nuclear export of pre-ribosomal particles. Nmd3, a highly conserved protein in eukaryotes, is a specific adaptor required for the export of pre-60S particles. Here we used cryo-electron microscopy (cryo-EM) to characterize Saccharomyces cerevisiae pre-60S particles purified with epitope-tagged Nmd3. Our structural analysis indicates that these particles belong to a specific late stage of cytoplasmic pre-60S maturation in which ribosomal proteins uL16, uL10, uL11, eL40 and eL41 are deficient, but ribosome assembly factors Nmd3, Lsg1, Tif6 and Reh1 are present. Nmd3 and Lsg1 are located near the peptidyl-transferase center (PTC). In particular, Nmd3 recognizes the PTC in its near-mature conformation. In contrast, Reh1 is anchored to the exit of the polypeptide tunnel, with its C terminus inserted into the tunnel. These findings pinpoint a structural checkpoint role for Nmd3 in PTC assembly, and provide information about functional and mechanistic roles of these assembly factors in the maturation of the 60S ribosomal subunit.
核糖体生物合成中的一个关键步骤是核糖体前体颗粒的核输出。Nmd3是真核生物中一种高度保守的蛋白质，是60S核糖体前体颗粒输出所需的特异性衔接蛋白。在这里，我们使用冷冻电子显微镜（cryo-EM）来表征用表位标签Nmd3纯化的酿酒酵母60S核糖体前体颗粒。我们的结构分析表明，这些颗粒属于细胞质60S核糖体前体成熟的特定后期阶段，其中核糖体蛋白uL16、uL10、uL11、eL40和eL41缺失，但核糖体组装因子Nmd3、Lsg1、Tif6和Reh1存在。Nmd3和Lsg1位于肽基转移酶中心（PTC）附近。特别地，Nmd3以其接近成熟的构象识别PTC。相比之下，Reh1锚定在多肽通道的出口，其C末端插入通道。这些发现确定了Nmd3在PTC组装中的结构检查点作用，并提供了有关这些组装因子在60S核糖体亚基成熟中的功能和机制作用的信息。
