Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843;
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843.
Proc Natl Acad Sci U S A. 2020 Mar 24;117(12):6550-6558. doi: 10.1073/pnas.1920582117. Epub 2020 Mar 9.
The 1918 influenza A virus (IAV) caused the most severe flu pandemic in recorded human history. Nonstructural protein 1 (NS1) is an important virulence factor of the 1918 IAV. NS1 antagonizes host defense mechanisms through interactions with multiple host factors. One pathway by which NS1 increases virulence is through the activation of phosphoinositide 3-kinase (PI3K) by binding to its p85β subunit. Here we present the mechanism underlying the molecular recognition of the p85β subunit by 1918 NS1. Using X-ray crystallography, we determine the structure of 1918 NS1 complexed with p85β of human PI3K. We find that the 1918 NS1 effector domain (1918 NS1) undergoes a conformational change to bind p85β. Using NMR relaxation dispersion and molecular dynamics simulation, we identify that free 1918 NS1 exists in a dynamic equilibrium between p85β-binding-competent and -incompetent conformations in the submillisecond timescale. Moreover, we discover that NS1 proteins of 1918 (H1N1) and Udorn (H3N2) strains exhibit drastically different conformational dynamics and binding kinetics to p85β. These results provide evidence of strain-dependent conformational dynamics of NS1. Using kinetic modeling based on the experimental data, we demonstrate that 1918 NS1 can result in the faster hijacking of p85β compared to Ud NS1, although the former has a lower affinity to p85β than the latter. Our results suggest that the difference in binding kinetics may impact the competition with cellular antiviral responses for the activation of PI3K. We anticipate that our findings will increase the understanding of the strain-dependent behaviors of influenza NS1 proteins.
1918 年甲型流感病毒（IAV）引发了有记录以来人类历史上最严重的流感大流行。非结构蛋白 1（NS1）是 1918 年 IAV 的一个重要毒力因子。NS1 通过与多种宿主因子相互作用拮抗宿主防御机制。NS1 增加毒力的一种途径是通过与 p85β亚基结合激活磷酸肌醇 3-激酶（PI3K）。在这里，我们提出了 1918 NS1 与 p85β亚基分子识别的机制。我们使用 X 射线晶体学确定了 1918 NS1 与人 PI3K 的 p85β 亚基复合物的结构。我们发现 1918 NS1 的效应结构域（1918 NS1）发生构象变化以结合 p85β。通过 NMR 弛豫弥散和分子动力学模拟，我们发现游离的 1918 NS1 在亚毫秒时间尺度上以结合 p85β的竞争和非竞争构象之间的动态平衡存在。此外，我们发现 1918 年（H1N1）和 Udorn（H3N2）株的 NS1 蛋白表现出截然不同的构象动力学和与 p85β的结合动力学。这些结果为 NS1 的株依赖性构象动力学提供了证据。使用基于实验数据的动力学建模，我们证明与 Ud NS1 相比，1918 NS1 可以更快地劫持 p85β，尽管前者与 p85β 的亲和力低于后者。我们的结果表明，结合动力学的差异可能会影响 PI3K 激活与细胞抗病毒反应的竞争。我们预计我们的发现将增加对流感 NS1 蛋白株依赖性行为的理解。
