The intrinsically disordered CARDs-Helicase linker in RIG-I is a molecular gate for RNA proofreading.
The intrinsically disordered CARDs-Helicase linker in RIG-I is a molecular gate for RNA proofreading.
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DOI：
10.15252/embj.2021109782
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发表时间：
2022-05-16
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先天免疫受体RIG-I提供了抵抗病毒感染的第一道防线。病毒RNA被RIG-I的C末端结构域（CTD）识别，但RNA必须接合解旋酶结构域以从其自身抑制性CARD 2：Hel 2 i相互作用中释放信号传导CARD（半胱天冬酶激活和募集结构域）结构域。由于解旋酶本身缺乏RNA特异性，因此必须存在校正RNA进入解旋酶结构域的机制。尽管这些机制在预防非特异性RNA引起的异常免疫应答中至关重要，但迄今为止它们在很大程度上仍未被表征。这项研究揭示了一种以前未知的校对机制，通过这种机制，RIG-I确保解旋酶与CTD明确识别的RNA结合。这种机制的一个关键部分涉及本质上无序的CARDs-解旋酶接头（CHL），它将CARDs连接到解旋酶亚结构域Hel 1。CHL使用其带负电荷的区域来静电拮抗传入的RNA。除了这种RNA门控功能之外，CHL对于CARD 2：Hel 2 i界面的稳定是必不可少的。总的来说，我们发现CHL和CARD 2：Hel 2 i界面共同作用，建立了一种可调的门控机制，允许CTD选择的RNA结合解旋酶结构域，同时阻断非特异性RNA。这些发现还表明，CHL可以代表基于RIG-I的治疗的新靶点。RNA结合介导的RIG-I活化的特异性通过涉及CHL和CARD：Hel 2 i界面的门控机制来确保。
The innate immune receptor RIG‐I provides a first line of defense against viral infections. Viral RNAs are recognized by RIG‐I's C‐terminal domain (CTD), but the RNA must engage the helicase domain to release the signaling CARD (Caspase Activation and Recruitment Domain) domains from their autoinhibitory CARD2:Hel2i interactions. Because the helicase itself lacks RNA specificity, mechanisms to proofread RNAs entering the helicase domain must exist. Although such mechanisms would be crucial in preventing aberrant immune responses by non‐specific RNAs, they remain largely uncharacterized to date. This study reveals a previously unknown proofreading mechanism through which RIG‐I ensures that the helicase engages RNAs explicitly recognized by the CTD. A crucial part of this mechanism involves the intrinsically disordered CARDs‐Helicase Linker (CHL), which connects the CARDs to the helicase subdomain Hel1. CHL uses its negatively charged regions to antagonize incoming RNAs electrostatically. In addition to this RNA gating function, CHL is essential for stabilization of the CARD2:Hel2i interface. Overall, we uncover that the CHL and CARD2:Hel2i interface work together to establish a tunable gating mechanism that allows CTD‐chosen RNAs to bind the helicase domain, while at the same time blocking non‐specific RNAs. These findings also indicate that CHL could represent a novel target for RIG‐I‐based therapeutics. Specificity for RNA‐binding mediated activation of RIG‐I is ensured by a gating mechanism involving the CHL and CARD:Hel2i interface.