Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA.
Sci Adv. 2024 Apr 19;10(16):eadl6144. doi: 10.1126/sciadv.adl6144.
Nucleoprotein (NP) is a key structural protein of influenza ribonucleoprotein complexes and is central to viral RNA packing and trafficking. NP also determines the sensitivity of influenza to myxovirus resistance protein 1 (MxA), an innate immunity factor that restricts influenza replication. A few critical MxA-resistant mutations have been identified in NP, including the highly conserved proline-283 substitution. This essential proline-283 substitution impairs influenza growth, a fitness defect that becomes particularly prominent at febrile temperature (39°C) when host chaperones are depleted. Here, we biophysically characterize proline-283 NP and serine-283 NP to test whether the fitness defect is caused by the proline-283 substitution introducing folding defects. We show that the proline-283 substitution changes the folding pathway of NP, making NP more aggregation prone during folding, but does not alter the native structure of the protein. 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.
核蛋白（NP）是流感核糖核蛋白复合物的关键结构蛋白，是病毒 RNA 包装和运输的核心。NP 还决定了流感对粘病毒抵抗蛋白 1（MxA）的敏感性，MxA 是一种限制流感复制的先天免疫因子。NP 中已经确定了几个关键的 MxA 抗性突变，包括高度保守的脯氨酸-283 取代。这个必需的脯氨酸-283 取代会损害流感的生长，当宿主伴侣蛋白耗尽时，在发热温度（39°C）下，这种适应性缺陷会变得尤为明显。在这里，我们通过生物物理特性分析脯氨酸-283 NP 和丝氨酸-283 NP，以测试适应性缺陷是否是由脯氨酸-283 取代引入的折叠缺陷引起的。我们发现脯氨酸-283 取代改变了 NP 的折叠途径，使 NP 在折叠过程中更容易聚集，但不会改变蛋白质的天然结构。这些发现表明，流感已经进化到劫持宿主伴侣蛋白来促进折叠那些原本在生物物理上无法胜任的病毒蛋白，从而逃避先天免疫系统。
