Adu-Gyamfi Emmanuel, Kim Lori S, Jardetzky Theodore S, Lamb Robert A
Department of Molecular Biosciences, Northwestern University, Evanston, Illinois, USA.
Department of Structural Biology, Stanford University, Stanford, California, USA.
J Virol. 2016 Aug 12;90(17):7778-88. doi: 10.1128/JVI.00896-16. Print 2016 Sep 1.
Paramyxoviridae consist of a large family of enveloped, negative-sense, nonsegmented single-stranded RNA viruses that account for a significant number of human and animal diseases. The fusion process for nearly all paramyxoviruses involves the mixing of the host cell plasma membrane and the virus envelope in a pH-independent fashion. Fusion is orchestrated via the concerted action of two surface glycoproteins: an attachment protein called hemagglutinin-neuraminidase (HN [also called H or G depending on virus type and substrate]), which acts as a receptor binding protein, and a fusion (F) protein, which undergoes a major irreversible refolding process to merge the two membranes. Recent biochemical evidence suggests that receptor binding by HN is dispensable for cell-cell fusion. However, factors that influence the stability and/or conformation of the HN 4-helix bundle (4HB) stalk have not been studied. Here, we used oxidative cross-linking as well as functional assays to investigate the role of the structurally unresolved membrane-proximal stalk region (MPSR) (residues 37 to 58) of HN in the context of headless and full-length HN membrane fusion promotion. Our data suggest that the receptor binding head serves to stabilize the stalk to regulate fusion. Moreover, we found that the MPSR of HN modulates receptor binding and neuraminidase activity without a corresponding regulation of F triggering.
Paramyxoviruses require two viral membrane glycoproteins, the attachment protein variously called HN, H, or G and the fusion protein (F), to couple host receptor recognition to virus-cell fusion. The HN protein has a globular head that is attached to a membrane-anchored flexible stalk of ∼80 residues and has three activities: receptor binding, neuraminidase, and fusion activation. In this report, we have identified the functional significance of the membrane-proximal stalk region (MPSR) (HN, residues 37 to 56) of the paramyxovirus parainfluenza virus (PIV5), a region of the HN stalk that has not had its structure determined by X-ray crystallography. Our data suggest that the MPSR influences receptor binding and neuraminidase activity via an indirect mechanism. Moreover, the receptor binding head group stabilizes the 4HB stalk as part of the general mechanism to fine-tune F-activation.
副粘病毒科由一大类包膜的、负链、不分节段的单链RNA病毒组成，这些病毒导致了大量的人类和动物疾病。几乎所有副粘病毒的融合过程都涉及宿主细胞质膜和病毒包膜以不依赖pH的方式混合。融合是通过两种表面糖蛋白的协同作用来精心安排的：一种称为血凝素神经氨酸酶（HN，根据病毒类型和底物也称为H或G）的附着蛋白，它作为受体结合蛋白，以及一种融合（F）蛋白，该蛋白经历一个主要的不可逆重折叠过程以融合两个膜。最近的生化证据表明，HN与受体的结合对于细胞间融合是可有可无的。然而，影响HN 4 - 螺旋束（4HB）柄稳定性和/或构象的因素尚未得到研究。在这里，我们使用氧化交联以及功能测定来研究在无头和全长HN促进膜融合的背景下，HN结构未解析的膜近端柄区域（MPSR）（第37至58位氨基酸残基）的作用。我们的数据表明，受体结合头部用于稳定柄以调节融合。此外，我们发现HN的MPSR调节受体结合和神经氨酸酶活性，而没有对F触发进行相应调节。
副粘病毒需要两种病毒膜糖蛋白，即分别称为HN、H或G的附着蛋白和融合蛋白（F），以将宿主受体识别与病毒 - 细胞融合联系起来。HN蛋白有一个球状头部，连接到一个由约80个氨基酸残基组成的膜锚定柔性柄上，具有三种活性：受体结合、神经氨酸酶和融合激活。在本报告中，我们确定了副粘病毒副流感病毒（PIV5）的膜近端柄区域（MPSR）（HN，第37至56位氨基酸残基）的功能意义，该区域是HN柄的一个尚未通过X射线晶体学确定其结构的区域。我们的数据表明，MPSR通过间接机制影响受体结合和神经氨酸酶活性。此外，受体结合头部基团稳定4HB柄，作为微调F激活的一般机制的一部分。
