Structural Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA.
Mol Cell. 2011 Jul 22;43(2):299-310. doi: 10.1016/j.molcel.2011.06.001. Epub 2011 Jun 16.
Physical interaction between the phosphorylated RNA polymerase II carboxyl-terminal domain (CTD) and cellular capping enzymes is required for efficient formation of the 5' mRNA cap, the first modification of nascent mRNA. Here, we report the crystal structure of the RNA guanylyltransferase component of mammalian capping enzyme (Mce) bound to a CTD phosphopeptide. The CTD adopts an extended β-like conformation that docks Tyr1 and Ser5-PO(4) onto the Mce nucleotidyltransferase domain. Structure-guided mutational analysis verified that the Mce-CTD interface is a tunable determinant of CTD binding and stimulation of guanylyltransferase activity, and of Mce function in vivo. The location and composition of the CTD binding site on mammalian capping enzyme is distinct from that of a yeast capping enzyme that recognizes the same CTD primary structure. Thus, capping enzymes from different taxa have evolved different strategies to read the CTD code.
磷酸化 RNA 聚合酶 II C 末端结构域 (CTD) 与细胞加帽酶之间的物理相互作用是有效形成 5' mRNA 帽的必要条件，mRNA 帽是新生 mRNA 的第一个修饰。在这里，我们报告了与 CTD 磷酸肽结合的哺乳动物加帽酶 (Mce) 的 RNA 鸟苷转移酶成分的晶体结构。CTD 采用延伸的 β 样构象，将 Tyr1 和 Ser5-PO(4) 对接至 Mce 核苷酸转移酶结构域。结构导向的突变分析证实，Mce-CTD 界面是 CTD 结合和鸟苷转移酶活性以及 Mce 在体内功能的可调决定因素。哺乳动物加帽酶上的 CTD 结合位点的位置和组成与识别相同 CTD 一级结构的酵母加帽酶不同。因此，来自不同分类群的加帽酶已经进化出不同的策略来读取 CTD 密码。
