Blomqvist Ebba K, Bracci Nicole, Winstone Helena, Watkins J Monty, Weiss Susan R, Burke James M
Department of Molecular Medicine, The Herbert Wertheim University of Florida Scripps Institute for Biomedical Innovation and Technology, Jupiter, FL, USA.
Department of Immunology and Microbiology, The Herbert Wertheim University of Florida Scripps Institute for Biomedical Innovation and Technology, Jupiter, FL, USA.
bioRxiv. 2025 Aug 22:2025.08.18.670656. doi: 10.1101/2025.08.18.670656.
Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic virus that antagonizes innate immune responses, including the protein kinase R (PKR) pathway. Here, we examine the process of PKR activation in response to an immunostimulatory MERS-CoV mutant encoding an inactive endoribonuclease U and a deletion of accessory protein NS4a. We show that PKR condenses and activates on viral dsRNA proximal to viral double-membrane vesicles (DMVs). Condensates composed of activated PKR disassociate from dsRNA and dissolve, releasing activated PKR molecules into the cytosol where they phosphorylate eIF2α to initiate the integrated stress response. MERS-CoV NS4a protein prevents PKR activation by condensing on dsRNA and occluding PKR binding. Lastly, PKR condensation coincided with its activation in response to Zika virus. These findings establish a comprehensive model for PKR activation in response to positive-strand RNA viruses that replicate within membrane-associated complexes and elucidate how MERS-CoV antagonizes this crucial antiviral pathway.
中东呼吸综合征冠状病毒（MERS-CoV）是一种高致病性病毒，它能对抗包括蛋白激酶R（PKR）途径在内的先天免疫反应。在此，我们研究了PKR在响应一种编码无活性核糖核酸酶U且缺失辅助蛋白NS4a的免疫刺激性MERS-CoV突变体时的激活过程。我们发现，PKR在靠近病毒双膜囊泡（DMV）的病毒双链RNA上浓缩并激活。由活化的PKR组成的凝聚物从双链RNA上解离并溶解，将活化的PKR分子释放到细胞质中，在那里它们磷酸化真核生物翻译起始因子2α（eIF2α）以启动综合应激反应。MERS-CoV NS4a蛋白通过在双链RNA上凝聚并阻止PKR结合来防止PKR激活。最后，PKR凝聚与其对寨卡病毒的激活同时发生。这些发现建立了一个针对在膜相关复合物内复制的正链RNA病毒响应中PKR激活的全面模型，并阐明了MERS-CoV如何对抗这一关键的抗病毒途径。
