Research Group Mechanisms and Regulation of Splicing, The Institute of Cancer Research, London, UK.
Cluster of Excellence Multiscale Bioimaging (MBExC), Universitätsmedizin Göttingen, Göttingen, Germany.
Nat Commun. 2021 Jul 23;12(1):4491. doi: 10.1038/s41467-021-24741-1.
Intron selection during the formation of prespliceosomes is a critical event in pre-mRNA splicing. Chemical modulation of intron selection has emerged as a route for cancer therapy. Splicing modulators alter the splicing patterns in cells by binding to the U2 snRNP (small nuclear ribonucleoprotein)-a complex chaperoning the selection of branch and 3' splice sites. Here we report crystal structures of the SF3B module of the U2 snRNP in complex with spliceostatin and sudemycin FR901464 analogs, and the cryo-electron microscopy structure of a cross-exon prespliceosome-like complex arrested with spliceostatin A. The structures reveal how modulators inactivate the branch site in a sequence-dependent manner and stall an E-to-A prespliceosome intermediate by covalent coupling to a nucleophilic zinc finger belonging to the SF3B subunit PHF5A. These findings support a mechanism of intron recognition by the U2 snRNP as a toehold-mediated strand invasion and advance an unanticipated drug targeting concept.
剪接体形成过程中的内含子选择是前体 mRNA 剪接的一个关键事件。化学调控内含子选择已成为癌症治疗的一种途径。剪接调节剂通过与 U2 snRNP（小核核糖核蛋白）-一个指导分支和 3' 剪接位点选择的复合物结合，改变细胞中的剪接模式。在这里，我们报告了 U2 snRNP 的 SF3B 模块与 spliceostatin 和 sudemycin FR901464 类似物复合物的晶体结构，以及用 spliceostatin A 捕获的交叉外显子前剪接体样复合物的低温电子显微镜结构。这些结构揭示了调节剂如何以序列依赖性的方式使分支位点失活，并通过与属于 SF3B 亚基 PHF5A 的亲核锌指共价偶联，使 E 到 A 的前剪接体中间物停滞不前。这些发现支持了 U2 snRNP 通过 toehold 介导的链入侵识别内含子的机制，并提出了一个出乎意料的药物靶向概念。
