Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China.
Technology Center for Protein Sciences, Ministry of Education Key Laboratory of Protein Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Cell Res. 2018 Mar;28(3):307-322. doi: 10.1038/cr.2018.14. Epub 2018 Jan 23.
During each cycle of pre-mRNA splicing, the pre-catalytic spliceosome (B complex) is converted into the activated spliceosome (B complex), which has a well-formed active site but cannot proceed to the branching reaction. Here, we present the cryo-EM structure of the human B complex in three distinct conformational states. The EM map allows atomic modeling of nearly all protein components of the U2 small nuclear ribonucleoprotein (snRNP), including three of the SF3a complex and seven of the SF3b complex. The structure of the human B complex contains 52 proteins, U2, U5, and U6 small nuclear RNA (snRNA), and a pre-mRNA. Three distinct conformations have been captured, representing the early, mature, and late states of the human B complex. These complexes differ in the orientation of the Switch loop of Prp8, the splicing factors RNF113A and NY-CO-10, and most components of the NineTeen complex (NTC) and the NTC-related complex. Analysis of these three complexes and comparison with the B and C complexes reveal an ordered flux of components in the B-to-B and the B-to-B transitions, which ultimately prime the active site for the branching reaction.
在每个前体 mRNA 剪接周期中，前催化剪接体（B 复合物）转化为激活剪接体（B 复合物），后者具有形成良好的活性位点，但不能进行分支反应。在这里，我们展示了三种不同构象状态的人 B 复合物的冷冻电镜结构。EM 图谱允许对 U2 小核核糖核蛋白（snRNP）的几乎所有蛋白质成分进行原子建模，包括三个 SF3a 复合物和七个 SF3b 复合物。人 B 复合物的结构包含 52 种蛋白质、U2、U5 和 U6 小核 RNA（snRNA）以及前体 mRNA。已捕获到三种不同的构象，分别代表人 B 复合物的早期、成熟和晚期状态。这些复合物在 Prp8 的 Switch 环、剪接因子 RNF113A 和 NY-CO-10 的取向以及 NineTeen 复合物（NTC）和 NTC 相关复合物的大多数成分方面存在差异。对这三个复合物的分析以及与 B 和 C 复合物的比较表明，B 到 B 和 B 到 C 转变中的组分有序流动，这最终为分支反应激活活性位点。
