Department of Biochemistry, Max Planck Institute for Developmental Biology, Spemannstrasse 35, 72076 Tübingen, Germany.
Nucleic Acids Res. 2012 Nov;40(21):11058-72. doi: 10.1093/nar/gks883. Epub 2012 Sep 12.
The CCR4-NOT complex plays a crucial role in post-transcriptional mRNA regulation in eukaryotic cells. It catalyzes the removal of mRNA poly(A) tails, thereby repressing translation and committing mRNAs to decay. The conserved core of the complex consists of a catalytic module comprising two deadenylases (CAF1/POP2 and CCR4a/b) and the NOT module, which contains at least NOT1, NOT2 and NOT3. NOT1 bridges the interaction between the two modules and therefore, acts as a scaffold protein for the assembly of the complex. Here, we present the crystal structures of the CAF1-binding domain of human NOT1 alone and in complex with CAF1. The NOT1 domain comprises five helical hairpins that adopt an MIF4G (middle portion of eIF4G) fold. This NOT1 MIF4G domain binds CAF1 through a pre-formed interface and leaves the CAF1 catalytic site fully accessible to RNA substrates. The conservation of critical structural and interface residues suggests that the NOT1 MIF4G domain adopts a similar fold and interacts with CAF1 in a similar manner in all eukaryotes. Our findings shed light on the assembly of the CCR4-NOT complex and provide the basis for dissecting the role of the NOT module in mRNA deadenylation.
CCR4-NOT 复合物在真核细胞中转录后 mRNA 调控中发挥着关键作用。它催化 mRNA 多聚（A）尾的去除，从而抑制翻译并促使 mRNA 降解。该复合物的保守核心由包含两个脱腺苷酶（CAF1/POP2 和 CCR4a/b）的催化模块和 NOT 模块组成，NOT 模块至少包含 NOT1、NOT2 和 NOT3。NOT1 桥接两个模块之间的相互作用，因此作为复合物组装的支架蛋白。在这里，我们单独展示了人源 NOT1 的 CAF1 结合域的晶体结构及其与 CAF1 的复合物结构。NOT1 结构域包含五个螺旋发夹，采用 MIF4G（eIF4G 的中部）折叠。NOT1 MIF4G 结构域通过预先形成的界面与 CAF1 结合，并使 CAF1 催化位点完全可与 RNA 底物接触。关键结构和界面残基的保守性表明，NOT1 MIF4G 结构域在所有真核生物中采用相似的折叠方式并以相似的方式与 CAF1 相互作用。我们的发现阐明了 CCR4-NOT 复合物的组装，并为剖析 NOT 模块在 mRNA 脱腺苷酸化中的作用提供了基础。
