Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
Mol Cell. 2018 Dec 20;72(6):999-1012.e6. doi: 10.1016/j.molcel.2018.10.012. Epub 2018 Nov 15.
Double-stranded RNA (dsRNA) is a potent proinflammatory signature of viral infection. Long cytosolic dsRNA is recognized by MDA5. The cooperative assembly of MDA5 into helical filaments on dsRNA nucleates the assembly of a multiprotein type I interferon signaling platform. Here, we determined cryoelectron microscopy (cryo-EM) structures of MDA5-dsRNA filaments with different helical twists and bound nucleotide analogs at resolutions sufficient to build and refine atomic models. The structures identify the filament-forming interfaces, which encode the dsRNA binding cooperativity and length specificity of MDA5. The predominantly hydrophobic interface contacts confer flexibility, reflected in the variable helical twist within filaments. Mutation of filament-forming residues can result in loss or gain of signaling activity. Each MDA5 molecule spans 14 or 15 RNA base pairs, depending on the twist. Variations in twist also correlate with variations in the occupancy and type of nucleotide in the active site, providing insights on how ATP hydrolysis contributes to MDA5-dsRNA recognition.
双链 RNA（dsRNA）是病毒感染的一种有效的促炎特征。长细胞质 dsRNA被 MDA5 识别。MDA5 在 dsRNA 核上的螺旋丝的协同组装引发了多种蛋白 I 型干扰素信号平台的组装。在这里，我们通过低温电子显微镜（cryo-EM）确定了具有不同螺旋扭曲和结合核苷酸类似物的 MDA5-dsRNA 纤维的结构，分辨率足以构建和细化原子模型。这些结构确定了纤维形成的界面，这些界面编码了 MDA5 的 dsRNA 结合协同性和长度特异性。主要的疏水性界面接触赋予了灵活性，这反映在纤维内可变的螺旋扭曲中。纤维形成残基的突变可能导致信号活性的丧失或获得。每个 MDA5 分子跨越 14 或 15 个 RNA 碱基对，具体取决于扭曲度。扭曲的变化也与活性位点中核苷酸的占据和类型相关，这为了解 ATP 水解如何有助于 MDA5-dsRNA 的识别提供了线索。
