Byrd-Leotis Lauren, Galloway Summer E, Agbogu Evangeline, Steinhauer David A
Department of Microbiology and Immunology, Rollins Research Center, Emory University School of Medicine, Atlanta, Georgia, USA.
Department of Microbiology and Immunology, Rollins Research Center, Emory University School of Medicine, Atlanta, Georgia, USA
J Virol. 2015 Apr;89(8):4504-16. doi: 10.1128/JVI.00057-15. Epub 2015 Feb 4.
Influenza A viruses enter host cells through endosomes, where acidification induces irreversible conformational changes of the viral hemagglutinin (HA) that drive the membrane fusion process. The prefusion conformation of the HA is metastable, and the pH of fusion can vary significantly among HA strains and subtypes. Furthermore, an accumulating body of evidence implicates HA stability properties as partial determinants of influenza host range, transmission phenotype, and pathogenic potential. Although previous studies have identified HA mutations that can affect HA stability, these have been limited to a small selection of HA strains and subtypes. Here we report a mutational analysis of HA stability utilizing a panel of expressed HAs representing a broad range of HA subtypes and strains, including avian representatives across the phylogenetic spectrum and several human strains. We focused on two highly conserved residues in the HA stem region: HA2 position 58, located at the membrane distal tip of the short helix of the hairpin loop structure, and HA2 position 112, located in the long helix in proximity to the fusion peptide. We demonstrate that a K58I mutation confers an acid-stable phenotype for nearly all HAs examined, whereas a D112G mutation consistently leads to elevated fusion pH. The results enhance our understanding of HA stability across multiple subtypes and provide an additional tool for risk assessment for circulating strains that may have other hallmarks of human adaptation. Furthermore, the K58I mutants, in particular, may be of interest for potential use in the development of vaccines with improved stability profiles.
The influenza A hemagglutinin glycoprotein (HA) mediates the receptor binding and membrane fusion functions that are essential for virus entry into host cells. While receptor binding has long been recognized for its role in host species specificity and transmission, membrane fusion and associated properties of HA stability have only recently been appreciated as potential determinants. We show here that mutations can be introduced at highly conserved positions to stabilize or destabilize the HA structure of multiple HA subtypes, expanding our knowledge base for this important phenotype. The practical implications of these findings extend to the field of vaccine design, since the HA mutations characterized here could potentially be utilized across a broad spectrum of influenza virus subtypes to improve the stability of vaccine strains or components.
甲型流感病毒通过内体进入宿主细胞，在内体中酸化会诱导病毒血凝素（HA）发生不可逆的构象变化，从而驱动膜融合过程。HA的预融合构象是亚稳态的，并且融合pH值在HA毒株和亚型之间可能有显著差异。此外，越来越多的证据表明，HA的稳定性特性是流感宿主范围、传播表型和致病潜力的部分决定因素。尽管先前的研究已经确定了可能影响HA稳定性的HA突变，但这些研究仅限于少数几种HA毒株和亚型。在这里，我们报告了一项对HA稳定性的突变分析，使用了一组表达的HA，它们代表了广泛的HA亚型和毒株，包括系统发育谱中的禽类代表以及几种人类毒株。我们关注HA茎区的两个高度保守的残基：位于发夹环结构短螺旋膜远端末端的HA2位置58，以及位于靠近融合肽的长螺旋中的HA2位置112。我们证明，K58I突变几乎赋予所有检测的HA一种酸稳定表型，而D112G突变始终导致融合pH值升高。这些结果增进了我们对多种亚型HA稳定性的理解，并为可能具有其他人类适应性特征的流行毒株的风险评估提供了一个额外的工具。此外，特别是K58I突变体，可能在开发具有改善稳定性特征的疫苗方面具有潜在用途。
甲型流感血凝素糖蛋白（HA）介导受体结合和膜融合功能，这些功能对于病毒进入宿主细胞至关重要。虽然受体结合在宿主物种特异性和传播中的作用早已得到认可，但HA的膜融合及相关稳定性特性直到最近才被视为潜在的决定因素。我们在此表明，可以在高度保守的位置引入突变，以稳定或破坏多种HA亚型的HA结构，扩展了我们对这一重要表型的知识库。这些发现的实际意义延伸到疫苗设计领域，因为这里所表征的HA突变有可能在广泛的流感病毒亚型中用于提高疫苗毒株或组分的稳定性。
