Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, CO, 80045, USA.
Colorado School of Mines, Golden, CO, 80401, USA.
Nat Commun. 2021 Feb 4;12(1):793. doi: 10.1038/s41467-021-21039-0.
Adenosine-to-inosine (A-to-I) editing of eukaryotic cellular RNAs is essential for protection against auto-immune disorders. Editing is carried out by ADAR1, whose innate immune response-specific cytoplasmic isoform possesses a Z-DNA binding domain (Zα) of unknown function. Zα also binds to CpG repeats in RNA, which are a hallmark of Z-RNA formation. Unexpectedly, Zα has been predicted - and in some cases even shown - to bind to specific regions within mRNA and rRNA devoid of such repeats. Here, we use NMR, circular dichroism, and other biophysical approaches to demonstrate and characterize the binding of Zα to mRNA and rRNA fragments. Our results reveal a broad range of RNA sequences that bind to Zα and adopt Z-RNA conformations. Binding is accompanied by destabilization of neighboring A-form regions which is similar in character to what has been observed for B-Z-DNA junctions. The binding of Zα to non-CpG sequences is specific, cooperative and occurs with an affinity in the low micromolar range. This work allows us to propose a model for how Zα could influence the RNA binding specificity of ADAR1.
真核细胞 RNA 的腺苷到肌苷（A-to-I）编辑对于预防自身免疫性疾病至关重要。编辑由 ADAR1 完成，其固有免疫反应特异性细胞质同工型具有未知功能的 Z-DNA 结合结构域（Zα）。Zα 还与 RNA 中的 CpG 重复序列结合，CpG 重复序列是 Z-RNA 形成的标志。出人意料的是，Zα 已被预测 - 在某些情况下甚至已被证明 - 与缺乏此类重复序列的 mRNA 和 rRNA 的特定区域结合。在这里，我们使用 NMR、圆二色性和其他生物物理方法来证明和表征 Zα 与 mRNA 和 rRNA 片段的结合。我们的结果揭示了与 Zα 结合并采用 Z-RNA 构象的广泛 RNA 序列。结合伴随着邻近 A 构象区域的失稳，其性质与已观察到的 B-Z-DNA 接头相似。Zα 与非 CpG 序列的结合是特异性的、协同的，亲和力在低微摩尔范围内。这项工作使我们能够提出一个模型，说明 Zα 如何影响 ADAR1 的 RNA 结合特异性。
