Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, QLD 4072, Australia.
Viruses. 2017 Nov 2;9(11):326. doi: 10.3390/v9110326.
West Nile virus (WNV) is a neurotropic flavivirus that can cause encephalitis in mammalian and avian hosts. In America, the virulent WNV strain (NY99) is causing yearly outbreaks of encephalitis in humans and horses, while in Australia the less virulent Kunjin strain of WNV strain has not been associated with significant disease outbreaks until a recent 2011 large outbreak in horses (but not in humans) caused by NSW2011 strain. Using chimeric viruses between NY99 and NSW2011 strains we previously identified a role for the non-structural proteins of NY99 strain and especially the NS3 protein, in enhanced virus replication in type I interferon response-competent cells and increased virulence in mice. To further define the role of NY99 NS3 protein in inhibition of type I interferon response, we have generated and characterised additional chimeric viruses containing the protease or the helicase domains of NY99 NS3 on the background of the NSW2011 strain. The results identified the role for the helicase but not the protease domain of NS3 protein in the inhibition of type I interferon signalling and showed that helicase domain of the more virulent NY99 strain performs this function more efficiently than helicase domain of the less virulent NSW2011 strain. Further analysis with individual amino acid mutants identified two amino acid residues in the helicase domain primarily responsible for this difference. Using chimeric replicons, we also showed that the inhibition of type I interferon (IFN) signalling was independent of other known functions of NS3 in RNA replication and assembly of virus particles.
西尼罗河病毒（WNV）是一种嗜神经黄病毒，可引起哺乳动物和禽类宿主的脑炎。在美国，强毒WNV 株（NY99）每年都会导致人类和马的脑炎暴发，而在澳大利亚，弱毒 Kunjin 株WNV 株尚未与重大疾病暴发相关，直到最近 2011 年在马（但不在人类）中暴发的 NSW2011 株。使用 NY99 和 NSW2011 株之间的嵌合病毒，我们先前确定了 NY99 株的非结构蛋白，特别是 NS3 蛋白，在 I 型干扰素反应有功能的细胞中增强病毒复制和在小鼠中增强毒力的作用。为了进一步确定 NY99 NS3 蛋白在抑制 I 型干扰素反应中的作用，我们生成并表征了含有 NY99 NS3 的蛋白酶或解旋酶结构域的其他嵌合病毒，背景为 NSW2011 株。结果确定了 NS3 蛋白的解旋酶结构域而不是蛋白酶结构域在抑制 I 型干扰素信号中的作用，并表明更毒力的 NY99 株的解旋酶结构域比低毒力的 NSW2011 株的解旋酶结构域更有效地执行此功能。用单个氨基酸突变体进行进一步分析，确定了该结构域中的两个氨基酸残基主要负责这种差异。使用嵌合复制子，我们还表明，I 型干扰素（IFN）信号的抑制与 NS3 在 RNA 复制和病毒粒子组装中的其他已知功能无关。
