Benton Donald J, Wharton Stephen A, Martin Stephen R, McCauley John W
Worldwide Influenza Centre, Francis Crick Institute, London, United Kingdom.
Structural Biology Science Technology Platform, Francis Crick Institute, London, United Kingdom.
J Virol. 2017 May 12;91(11). doi: 10.1128/JVI.02293-16. Print 2017 Jun 1.
Influenza A(H7N9) viruses have caused a large number of zoonotic infections since their emergence in 2013. They remain a public health concern due to the repeated high levels of infection with these viruses and their perceived pandemic potential. A major factor that determines influenza A virus fitness and therefore transmissibility is the interaction of the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA) with the cell surface receptor sialic acid. Typically, the HA is responsible for binding to the sialic acid to allow virus internalization and the NA is a sialidase responsible for cleaving sialic acid to aid virus spread and release. N9 NA has previously been shown to have receptor binding properties mediated by a sialic acid binding site, termed the hemadsorption (Hb) site, which is discrete from the enzymatically active sialidase site. This study investigated the N9 NA from a zoonotic H7N9 virus strain in order to determine its possible role in virus receptor binding. We demonstrate that this N9 NA has an active Hb site which binds to sialic acid, which enhances overall virus binding to sialic acid receptor analogues. We also show that the N9 NA can also contribute to receptor binding due to unusual kinetic characteristics of the sialidase site which specifically enhance binding to human-like α2,6-linked sialic acid receptors. The interaction of influenza A virus glycoproteins with cell surface receptors is a major determinant of infectivity and therefore transmissibility. Understanding these interactions is important for understanding which factors are necessary to determine pandemic potential. Influenza A viruses generally mediate binding to cell surface sialic acid receptors via the hemagglutinin (HA) glycoprotein, with the neuraminidase (NA) glycoprotein being responsible for cleaving the receptor to allow virus release. Previous studies showed that the NA proteins of the N9 subtype can bind sialic acid via a separate binding site distinct from the sialidase active site. This study demonstrates for purified protein and virus that the NA of the zoonotic H7N9 viruses has a binding capacity via both the secondary binding site and unusual kinetic properties of the sialidase site which promote receptor binding via this site and which enhance binding to human-like receptors. This could have implications for understanding human-to-human transmission of these viruses.
自2013年出现以来，甲型H7N9流感病毒已引发大量人畜共患感染。由于这些病毒反复出现的高感染水平及其被认为的大流行潜力，它们仍然是一个公共卫生问题。决定甲型流感病毒适应性进而决定其传播性的一个主要因素是表面糖蛋白血凝素（HA）和神经氨酸酶（NA）与细胞表面受体唾液酸的相互作用。通常，HA负责与唾液酸结合以使病毒内化，而NA是一种唾液酸酶，负责切割唾液酸以帮助病毒传播和释放。此前已表明，N9 NA具有由唾液酸结合位点介导的受体结合特性，该位点称为血细胞吸附（Hb）位点，与酶活性唾液酸酶位点不同。本研究调查了一种人畜共患H7N9病毒株的N9 NA，以确定其在病毒受体结合中的可能作用。我们证明，这种N9 NA具有一个与唾液酸结合的活性Hb位点，这增强了整体病毒与唾液酸受体类似物的结合。我们还表明，由于唾液酸酶位点不寻常的动力学特性，N9 NA也可促进受体结合，该特性特别增强了与人类样α2,6-连接唾液酸受体的结合。甲型流感病毒糖蛋白与细胞表面受体的相互作用是感染性进而传播性的主要决定因素。了解这些相互作用对于理解哪些因素是决定大流行潜力所必需的很重要。甲型流感病毒通常通过血凝素（HA）糖蛋白介导与细胞表面唾液酸受体的结合，神经氨酸酶（NA）糖蛋白负责切割受体以允许病毒释放。先前的研究表明，N9亚型的NA蛋白可通过一个与唾液酸酶活性位点不同的单独结合位点结合唾液酸。本研究针对纯化蛋白和病毒证明，人畜共患H7N9病毒的NA通过二级结合位点以及唾液酸酶位点的不寻常动力学特性具有结合能力，这些特性促进了通过该位点的受体结合并增强了与人类样受体的结合。这可能对理解这些病毒的人际传播有影响。
