State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Cells. 2019 Aug 5;8(8):836. doi: 10.3390/cells8080836.
Poly(A)-specific ribonuclease (PARN), a multifunctional multi-domain deadenylase, is crucial to the regulation of mRNA turnover and the maturation of various non-coding RNAs. Despite extensive studies of the well-folding domains responsible for PARN catalysis, the structure and function of the C-terminal domain (CTD) remains elusive. PARN is a cytoplasm-nucleus shuttle protein with concentrated nucleolar distribution. Here, we identify the nuclear and nucleolar localization signals in the CTD of PARN. Spectroscopic studies indicated that PARN-CTD is intrinsically disordered with loosely packed local structures/tertiary structure. Phosphorylation-mimic mutation S557D disrupted the local structure and facilitated the binding of the CTD with the well-folded domains, with no impact on PARN deadenylase activity. Under normal conditions, the nucleolus-residing PARN recruited CBP80 into the nucleoli to repress its deadenylase activity, while DNA damage-induced phosphorylation of PARN-S557 expelled CBP80 from the nucleoli to discharge activity inhibition and attracted nucleoplasm-located CstF-50 into the nucleoli to activate deadenylation. The structure switch-induced function switch of PARN reshaped the profile of small nuclear non-coding RNAs to respond to DNA damage. Our findings highlight that the structure switch of the CTD induced by posttranslational modifications redefines the subset of binding partners, and thereby the RNA targets in the nucleoli.
聚腺苷酸化特异性核糖核酸酶（PARN）是一种多功能的多结构域脱腺苷酸化酶，对调节 mRNA 周转率和各种非编码 RNA 的成熟至关重要。尽管对负责 PARN 催化的折叠良好的结构域进行了广泛的研究，但 C 端结构域（CTD）的结构和功能仍然难以捉摸。PARN 是一种胞质-核穿梭蛋白，在核仁中有集中分布。在这里，我们确定了 PARN CTD 中的核和核仁定位信号。光谱研究表明，PARN-CTD 是固有无序的，具有松散堆积的局部结构/三级结构。磷酸化模拟突变 S557D 破坏了局部结构并促进了 CTD 与折叠良好的结构域的结合，对 PARN 脱腺苷酸酶活性没有影响。在正常情况下，位于核仁中的 PARN 将 CBP80 招募到核仁中，以抑制其脱腺苷酸酶活性，而 PARN-S557 的 DNA 损伤诱导的磷酸化将 CBP80 从核仁中逐出，解除活性抑制，并吸引位于核质中的 CstF-50 进入核仁以激活脱腺苷酸化。PARN 的结构转换诱导的功能转换重塑了小核非编码 RNA 的特征，以响应 DNA 损伤。我们的发现强调了翻译后修饰诱导的 CTD 结构转换重新定义了结合伙伴子集，从而定义了核仁中的 RNA 靶标。
