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.

中文翻译：

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流感核蛋白中的免疫逃避脯氨酸 283 取代增加了聚集倾向而不改变天然结构

核蛋白 (NP) 是流感核糖核蛋白复合物的关键结构蛋白，对于病毒 RNA 包装和运输至关重要。 NP 还决定流感对粘病毒抗性蛋白 1 (MxA) 的敏感性，粘病毒抗性蛋白 1 是一种限制流感病毒复制的先天免疫因子。已在 NP 中鉴定出一些关键的 MxA 抗性突变，包括高度保守的脯氨酸 283 取代。这种必需的脯氨酸 283 取代会损害流感病毒的生长，这种健康缺陷在宿主伴侣耗尽时在发热温度 (39°C) 下变得尤为突出。在这里，我们对脯氨酸 283 NP 和丝氨酸 283 NP 进行生物物理表征，以测试适应性缺陷是否是由脯氨酸 283 取代引入折叠缺陷引起的。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，以促进其他生物物理上无能力的病毒蛋白的折叠，从而使先天免疫系统能够逃脱。