Department of Biochemistry, Max Planck Institute for Developmental Biology, Tübingen, D-72076, Germany.
Department of Protein Evolution, Max Planck Institute for Developmental Biology, Tübingen, D-72076, Germany.
RNA. 2018 Mar;24(3):381-395. doi: 10.1261/rna.064584.117. Epub 2017 Dec 18.
Bag-of-marbles (Bam) promotes germline stem cell (GSC) differentiation by repressing the expression of mRNAs encoding stem cell maintenance factors. Bam interacts with Benign gonial cell neoplasm (Bgcn) and the CCR4 deadenylase, a catalytic subunit of the CCR4-NOT complex. Bam has been proposed to bind CCR4 and displace it from the CCR4-NOT complex. Here, we investigated the interaction of Bam with the CCR4-NOT complex by using purified recombinant proteins. Unexpectedly, we found that Bam does not interact with CCR4 directly but instead binds to the CAF40 subunit of the complex in a manner mediated by a conserved N-terminal CAF40-binding motif (CBM). The crystal structure of the Bam CBM bound to CAF40 reveals that the CBM peptide adopts an α-helical conformation after binding to the concave surface of the crescent-shaped CAF40 protein. We further show that Bam-mediated mRNA decay and translational repression depend entirely on Bam's interaction with CAF40. Thus, Bam regulates the expression of its mRNA targets by recruiting the CCR4-NOT complex through interaction with CAF40.
豆包，帮我翻译一下这段英文吧：
袋状（Bam）通过抑制编码干细胞维持因子的 mRNA 的表达来促进生殖干细胞（GSC）分化。Bam 与良性精原细胞瘤（Bgcn）和 CCR4 脱腺苷酶相互作用，后者是 CCR4-NOT 复合物的催化亚基。有人提出 Bam 与 CCR4 结合并将其从 CCR4-NOT 复合物中置换出来。在这里，我们使用纯化的重组蛋白研究了 Bam 与 CCR4-NOT 复合物的相互作用。出乎意料的是，我们发现 Bam 并不直接与 CCR4 相互作用，而是通过保守的 N 端 CAF40 结合基序（CBM）介导与复合物的 CAF40 亚基结合。Bam CBM 与 CAF40 结合的晶体结构表明，CBM 肽在与 crescent 形 CAF40 蛋白的凹面结合后采用 α-螺旋构象。我们进一步表明，Bam 介导致密 mRNA 衰变和翻译抑制完全取决于 Bam 与 CAF40 的相互作用。因此，Bam 通过与 CAF40 相互作用招募 CCR4-NOT 复合物来调节其 mRNA 靶标表达。
