Mänz Benjamin, de Graaf Miranda, Mögling Ramona, Richard Mathilde, Bestebroer Theo M, Rimmelzwaan Guus F, Fouchier Ron A M
Department of Viroscience, Erasmus Medical Center, Rotterdam, The Netherlands.
Department of Viroscience, Erasmus Medical Center, Rotterdam, The Netherlands
J Virol. 2016 Jun 10;90(13):5928-5938. doi: 10.1128/JVI.00130-16. Print 2016 Jul 1.
A strong restriction of the avian influenza A virus polymerase in mammalian cells generally limits viral host-range switching. Although substitutions like E627K in the PB2 polymerase subunit can facilitate polymerase activity to allow replication in mammals, many human H5N1 and H7N9 viruses lack this adaptive substitution. Here, several previously unknown, naturally occurring, adaptive substitutions in PB2 were identified by bioinformatics, and their enhancing activity was verified using in vitro assays. Adaptive substitutions enhanced polymerase activity and virus replication in mammalian cells for avian H5N1 and H7N9 viruses but not for a partially human-adapted H5N1 virus. Adaptive substitutions toward basic amino acids were frequent and were mostly clustered in a putative RNA exit channel in a polymerase crystal structure. Phylogenetic analysis demonstrated divergent dependency of influenza viruses on adaptive substitutions. The novel adaptive substitutions found in this study increase basic understanding of influenza virus host adaptation and will help in surveillance efforts.
Influenza viruses from birds jump the species barrier into humans relatively frequently. Such influenza virus zoonoses may pose public health risks if the virus adapts to humans and becomes a pandemic threat. Relatively few amino acid substitutions-most notably in the receptor binding site of hemagglutinin and at positions 591 and 627 in the polymerase protein PB2-have been identified in pandemic influenza virus strains as determinants of host adaptation, to facilitate efficient virus replication and transmission in humans. Here, we show that substantial numbers of amino acid substitutions are functionally compensating for the lack of the above-mentioned mutations in PB2 and could facilitate influenza virus emergence in humans.
甲型禽流感病毒聚合酶在哺乳动物细胞中的强烈限制通常会限制病毒宿主范围的转换。尽管PB2聚合酶亚基中的E627K等替代可以促进聚合酶活性以允许在哺乳动物中复制，但许多人类H5N1和H7N9病毒缺乏这种适应性替代。在这里，通过生物信息学鉴定了PB2中几个以前未知的、自然发生的适应性替代，并使用体外试验验证了它们的增强活性。适应性替代增强了禽H5N1和H7N9病毒在哺乳动物细胞中的聚合酶活性和病毒复制，但对部分适应人类的H5N1病毒则没有作用。向碱性氨基酸的适应性替代很常见，并且大多聚集在聚合酶晶体结构中的一个假定的RNA出口通道中。系统发育分析表明流感病毒对适应性替代的依赖性不同。本研究中发现的新型适应性替代增加了对流感病毒宿主适应性的基本了解，并将有助于监测工作。
来自鸟类的流感病毒相对频繁地跨越物种屏障进入人类。如果这种流感病毒适应人类并成为大流行威胁，那么这种人畜共患流感病毒可能会带来公共卫生风险。在大流行性流感病毒株中，相对较少的氨基酸替代——最显著的是在血凝素的受体结合位点以及聚合酶蛋白PB2的591和627位——已被确定为宿主适应性的决定因素，以促进病毒在人类中的有效复制和传播。在这里，我们表明大量的氨基酸替代在功能上补偿了PB2中上述突变的缺乏，并可能促进流感病毒在人类中的出现。
