Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0QH, UK.
Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), University of Cambridge School of Clinical Medicine, Cambridge, CB2 0AW, UK.
Nat Commun. 2021 Nov 18;12(1):6668. doi: 10.1038/s41467-021-27062-5.
Our innate immune responses to viral RNA are vital defenses. Long cytosolic double-stranded RNA (dsRNA) is recognized by MDA5. The ATPase activity of MDA5 contributes to its dsRNA binding selectivity. Mutations that reduce RNA selectivity can cause autoinflammatory disease. Here, we show how the disease-associated MDA5 variant M854K perturbs MDA5-dsRNA recognition. M854K MDA5 constitutively activates interferon signaling in the absence of exogenous RNA. M854K MDA5 lacks ATPase activity and binds more stably to synthetic Alu:Alu dsRNA. CryoEM structures of MDA5-dsRNA filaments at different stages of ATP hydrolysis show that the K854 sidechain forms polar bonds that constrain the conformation of MDA5 subdomains, disrupting key steps in the ATPase cycle- RNA footprint expansion and helical twist modulation. The M854K mutation inhibits ATP-dependent RNA proofreading via an allosteric mechanism, allowing MDA5 to form signaling complexes on endogenous RNAs. This work provides insights on how MDA5 recognizes dsRNA in health and disease.
我们对病毒 RNA 的先天免疫反应是至关重要的防御机制。长细胞质双链 RNA（dsRNA）被 MDA5 识别。MDA5 的 ATP 酶活性有助于其 dsRNA 结合的选择性。降低 RNA 选择性的突变可能导致自身炎症性疾病。在这里，我们展示了与疾病相关的 MDA5 变体 M854K 如何干扰 MDA5-dsRNA 的识别。M854K MDA5 在没有外源性 RNA 的情况下，组成性地激活干扰素信号。M854K MDA5 缺乏 ATP 酶活性，并且与合成的 Alu:Alu dsRNA 结合更稳定。在不同 ATP 水解阶段的 MDA5-dsRNA 纤维的冷冻电镜结构表明，K854 侧链形成极性键，限制 MDA5 亚结构域的构象，破坏 ATP 酶循环中的关键步骤 - RNA 足迹扩展和螺旋扭曲调节。M854K 突变通过别构机制抑制 ATP 依赖性 RNA 校对，从而允许 MDA5 在内源性 RNA 上形成信号复合物。这项工作提供了关于 MDA5 在健康和疾病中如何识别 dsRNA 的见解。
