Yoon Jimin, Zhang Yu Meng, Her Cheenou, Grant Robert A, Ponomarenko Anna M, Ackermann Bryce E, Debelouchina Galia T, Shoulders Matthew D
bioRxiv. 2023 Sep 12:2023.09.08.556894. doi: 10.1101/2023.09.08.556894.
Nucleoprotein (NP) is a key structural protein of influenza ribonucleoprotein complexes and is central to viral RNA packing and trafficking. In human cells, the interferon induced Myxovirus resistance protein 1 (MxA) binds to NP and restricts influenza replication. This selection pressure has caused NP to evolve a few critical MxA-resistant mutations, particularly the highly conserved Pro283 substitution. Previous work showed that this essential Pro283 substitution impairs influenza growth, and the fitness defect becomes particularly prominent at febrile temperature (39 °C) when host chaperones are depleted. Here, we biophysically characterize Pro283 NP and Ser283 NP to test if the fitness defect is owing to Pro283 substitution introducing folding defects. We show that the Pro283 substitution changes the folding pathway of NP without altering the native structure, making NP more aggregation prone during folding. These findings suggest that influenza has evolved to hijack host chaperones to promote the folding of otherwise biophysically incompetent viral proteins that enable innate immune system escape.
Pro283 substitution in flu nucleoprotein introduces folding defects, and makes influenza uniquely dependent on host chaperones.
核蛋白（NP）是流感病毒核糖核蛋白复合体的关键结构蛋白，对病毒RNA的包装和运输至关重要。在人类细胞中，干扰素诱导的Mx蛋白1（MxA）与NP结合并限制流感病毒复制。这种选择压力导致NP发生了一些关键的抗MxA突变，特别是高度保守的Pro283位点的替换。先前的研究表明，这种关键的Pro283位点替换会损害流感病毒的生长，当宿主伴侣蛋白耗尽时，在发热温度（39°C）下适应性缺陷会变得尤为突出。在此，我们对Pro283 NP和Ser283 NP进行生物物理特性分析，以测试适应性缺陷是否归因于Pro283位点替换引入了折叠缺陷。我们发现Pro283位点替换改变了NP的折叠途径，但未改变其天然结构，使得NP在折叠过程中更容易聚集。这些发现表明，流感病毒已经进化出利用宿主伴侣蛋白来促进原本在生物物理性质上无法正常折叠的病毒蛋白的折叠，从而实现逃避免疫系统的目的。
流感病毒核蛋白中Pro283位点的替换引入了折叠缺陷，使流感病毒对宿主伴侣蛋白产生独特的依赖性。
