Zα domains are a subfamily of winged Helix-Turn-Helix (wHTH) domains found exclusively in proteins involved in the nucleic acids sensory pathway of vertebrate innate immune system and host evasion by viral pathogens. Interestingly, they are the only known protein domains that recognise the left-handed helical conformation of both dsDNA and dsRNA, known as Z-DNA and Z-RNA. Previously, it has been demonstrated that ADAR1 and ZBP1, two proteins possessing the Zα domains, localize to cytosolic stress granules. It was further speculated that such localization is principally mediated by Zα domains. To characterize and better understand such distinct and specific localization, we characterised the in vivo interactions and localization pattern for the amino terminal region of human DAI harbouring two Zα domains (ZαβDAI). Using immunoprecipitation and mass spectrometry, we identified several interacting partners that were components of the complex formed by Zα domains and RNAs. Differential interacting partners to wild-type Zα, relative to mutant proteins, demonstrated that most of the physiologically relevant interactions are mediated by the nucleic acid binding ability of the Zαβ. Further, we also show enrichment of selected complex components in cytoplasmic stress granules under conditions of stress. This ability is mostly lost in the mutants of ZαβDAI (ZαβDAI 4×mut) that lack nucleic-acid binding ability. Thus, we posit that the mechanism for the translocation of Zα domain-containing proteins to stress granules is mainly mediated by the nucleic acid binding ability of their Zα domains. Finally, we demonstrate that FUS and PSF/p54nrb, two RNA binding proteins with established roles in stress granules, interact with Zα, which provides strong evidence for a role of these proteins in the innate immune system.

中文翻译：

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Zα结构域在细胞质应激颗粒上的富集是由于其固有的结合核酸的能力

Zα结构域是有翅螺旋-螺旋-螺旋（wHTH）结构域的一个亚家族，仅存在于与脊椎动物先天免疫系统的核酸感觉途径和病毒病原体逃逸有关的蛋白质中。有趣的是，它们是识别dsDNA和dsRNA的左手螺旋构型的唯一已知蛋白质结构域，称为Z-DNA和Z-RNA。以前，已经证明了具有Zα域的两种蛋白质ADAR1和ZBP1定位于胞质应激颗粒。进一步推测这种定位主要是由Zα结构域介导的。为了表征和更好地理解这种独特和独特的定位，我们表征了具有两个Zα域（ZαβDAI）的人DAI氨基末端区域的体内相互作用和定位模式。使用免疫沉淀和质谱，我们确定了几个相互作用的伙伴，它们是由Zα域和RNA形成的复合物的组成部分。相对于突变蛋白，野生型Zα的不同相互作用伴侣表明，大多数生理相关的相互作用是由Zαβ的核酸结合能力介导的。此外，我们还显示了在胁迫条件下细胞质胁迫颗粒中所选复杂成分的富集。在缺乏核酸结合能力的ZαβDAI（ZαβDAI4xmut）突变体中，这种能力大部分丧失。因此，我们认为含Zα域的蛋白质易位到应激颗粒的机制主要是由它们的Zα域的核酸结合能力介导的。最后，我们证明FUS和PSF / p54nrb，