Institute of Molecular Biology and Biophysics, Eidgenössiche Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
Proc Natl Acad Sci U S A. 2014 May 6;111(18):E1852-61. doi: 10.1073/pnas.1323698111. Epub 2014 Apr 21.
The human RNA-editing enzyme adenosine deaminase acting on RNA (ADAR1) carries a unique nuclear localization signal (NLS) that overlaps one of its double-stranded RNA-binding domains (dsRBDs). This dsRBD-NLS is recognized by the nuclear import receptor transportin 1 (Trn1; also called karyopherin-β2) in an RNA-sensitive manner. Most Trn1 cargos bear a well-characterized proline-tyrosine-NLS, which is missing from the dsRBD-NLS. Here, we report the structure of the dsRBD-NLS, which reveals an unusual dsRBD fold extended by an additional N-terminal α-helix that brings the N- and C-terminal flanking regions in close proximity. We demonstrate experimentally that the atypical ADAR1-NLS is bimodular and is formed by the combination of the two flexible fragments flanking the folded domain. The intervening dsRBD acts only as an RNA-sensing scaffold, allowing the two NLS modules to be properly positioned for interacting with Trn1. We also provide a structural model showing how Trn1 can recognize the dsRBD-NLS and how dsRNA binding can interfere with Trn1 binding.
人类 RNA 编辑酶腺苷脱氨酶作用于 RNA（ADAR1）携带一个独特的核定位信号（NLS），该信号与它的双链 RNA 结合结构域（dsRBD）之一重叠。这种 dsRBD-NLS 以 RNA 敏感的方式被核输入受体转运蛋白 1（Trn1；也称为核孔蛋白-β2）识别。大多数 Trn1 货物都带有一个特征明确的脯氨酸-酪氨酸-NLS，而 dsRBD-NLS 中则没有。在这里，我们报告了 dsRBD-NLS 的结构，该结构揭示了一个不寻常的 dsRBD 折叠，由一个额外的 N 端α螺旋延伸，使 N 和 C 端侧翼区域紧密接近。我们通过实验证明，非典型的 ADAR1-NLS 是双模块的，由折叠结构域两侧的两个柔性片段组合而成。中间的 dsRBD 仅作为 RNA 感应支架，使两个 NLS 模块能够正确定位以与 Trn1 相互作用。我们还提供了一个结构模型，展示了 Trn1 如何识别 dsRBD-NLS 以及 dsRNA 结合如何干扰 Trn1 结合。
