Abstract：
Angiogenin, an RNase-A-family protein, promotes angiogenesis and has been implicated in cancer, neurodegenerative diseases and epigenetic inheritance1-10. After activation during cellular stress, angiogenin cleaves tRNAs at the anticodon loop, resulting in translation repression11-15. However, the catalytic activity of isolated angiogenin is very low, and the mechanisms of the enzyme activation and tRNA specificity have remained a puzzle3,16-23. Here we identify these mechanisms using biochemical assays and cryogenic electron microscopy (cryo-EM). Our study reveals that the cytosolic ribosome is the activator of angiogenin. A cryo-EM structure features angiogenin bound in the A site of the 80S ribosome. The C-terminal tail of angiogenin is rearranged by interactions with the ribosome to activate the RNase catalytic centre, making the enzyme several orders of magnitude more efficient in tRNA cleavage. Additional 80S-angiogenin structures capture how tRNA substrate is directed by the ribosome into angiogenin\'s active site, demonstrating that the ribosome acts as the specificity factor. Our findings therefore suggest that angiogenin is activated by ribosomes with a vacant A site, the abundance of which increases during cellular stress24-27. These results may facilitate the development of therapeutics to treat cancer and neurodegenerative diseases.
摘要：
血管生成素,RNaseA家族蛋白，促进血管生成并与癌症有关，神经退行性疾病，和表观遗传1-10。在细胞应激期间激活时，血管生成素在反密码子环处切割tRNA，导致翻译压抑11-15。分离的血管生成素的催化活性，然而,非常低，酶激活和tRNA特异性的机制仍然是一个难题3,16-23。这里,我们使用生化分析和低温电子显微镜发现这些机制。我们的工作表明，细胞溶质核糖体是血管生成素长期寻求的激活剂。2.8µ分辨率的低温EM结构特征是结合在80S核糖体A位点的血管生成素。血管生成素的C末端尾部通过与核糖体的相互作用而被重排以激活RNase催化中心,使酶在tRNA切割中更有效几个数量级。额外的80S•血管生成素结构捕获tRNA底物如何被核糖体引导进入血管生成素的活性位点,证明核糖体充当特异性因子。因此，我们的发现表明血管生成素被具有空A位点的核糖体激活，其丰度在细胞应激期间增加24-27。这些结果可能有助于开发治疗癌症和神经退行性疾病的疗法。
