Department of Molecular Biology, Princeton, NJ, 08544, USA.
Sci Rep. 2018 Nov 2;8(1):16294. doi: 10.1038/s41598-018-34615-0.
Nocturnin (NOCT) helps the circadian clock to adjust metabolism according to day and night activity. NOCT is upregulated in early evening and it has been proposed that NOCT serves as a deadenylase for metabolic enzyme mRNAs. We present a 2.7-Å crystal structure of the catalytic domain of human NOCT. Our structure shows that NOCT has a close overall similarity to CCR4 deadenylase family members, PDE12 and CNOT6L, and to a DNA repair enzyme TDP2. All the key catalytic residues present in PDE12, CNOT6L and TDP2 are conserved in NOCT and have the same conformations. However, we observe substantial differences in the surface properties of NOCT, an unexpectedly narrow active site pocket, and conserved structural elements in the vicinity of the catalytic center, which are unique to NOCT and absent in the deadenylases PDE12/CNOT6L. Moreover, we show that in contrast to human PDE12 and CNOT6L, NOCT is completely inactive against poly-A RNA. Our work thus reveals the structure of an intriguing circadian protein and suggests that NOCT has considerable differences from the related deadenylases, which may point to a unique cellular function of this enzyme.
夜蛋白（NOCT）帮助生物钟根据白天和黑夜的活动来调节代谢。NOCT 在傍晚时分上调，有人提出 NOCT 作为代谢酶 mRNAs 的脱腺苷酶。我们呈现了人源 NOCT 催化结构域的 2.7Å 晶体结构。我们的结构表明，NOCT 与 CCR4 脱腺苷酶家族成员 PDE12 和 CNOT6L 以及 DNA 修复酶 TDP2 具有紧密的整体相似性。所有存在于 PDE12、CNOT6L 和 TDP2 中的关键催化残基在 NOCT 中均被保守，且具有相同的构象。然而，我们观察到 NOCT 的表面性质、出人意料的狭窄活性口袋以及催化中心附近的保守结构元件存在显著差异，这些差异是 NOCT 所特有的，而在脱腺苷酶 PDE12/CNOT6L 中则不存在。此外，我们表明，与人类 PDE12 和 CNOT6L 相反，NOCT 对聚 A RNA 完全没有活性。我们的工作因此揭示了一个有趣的生物钟蛋白的结构，并表明 NOCT 与相关的脱腺苷酶存在相当大的差异，这可能指向该酶的独特细胞功能。
