Adu-Gyamfi Emmanuel, Kim Lori S, Jardetzky Theodore S, Lamb Robert A
Department of Molecular Biosciences, Northwestern University, Evanston, Illinois, USA.
Howard Hughes Medical Institute, Northwestern University, Evanston, Illinois, USA.
J Virol. 2016 Sep 29;90(20):9172-81. doi: 10.1128/JVI.01187-16. Print 2016 Oct 15.
The Paramyxoviridae comprise a large family of enveloped, negative-sense, single-stranded RNA viruses with significant economic and public health implications. For nearly all paramyxoviruses, infection is initiated by fusion of the viral and host cell plasma membranes in a pH-independent fashion. Fusion is orchestrated by the receptor binding protein hemagglutinin-neuraminidase (HN; also called H or G depending on the virus type) protein and a fusion (F) protein, the latter undergoing a major refolding process to merge the two membranes. Mechanistic details regarding the coupling of receptor binding to F activation are not fully understood. Here, we have identified the flexible loop region connecting the bulky enzymatically active head and the four-helix bundle stalk to be essential for fusion promotion. Proline substitution in this region of HN of parainfluenza virus 5 (PIV5) and Newcastle disease virus HN abolishes cell-cell fusion, whereas HN retains receptor binding and neuraminidase activity. By using reverse genetics, we engineered recombinant PIV5-EGFP viruses with mutations in the head-stalk linker region of HN. Mutations in this region abolished virus recovery and infectivity. In sum, our data suggest that the loop region acts as a "hinge" around which the bulky head of HN swings to-and-fro to facilitate timely HN-mediate F-triggering, a notion consistent with the stalk-mediated activation model of paramyxovirus fusion.
Paramyxovirus fusion with the host cell plasma membrane is essential for virus infection. Membrane fusion is orchestrated via interaction of the receptor binding protein (HN, H, or G) with the viral fusion glycoprotein (F). Two distinct models have been suggested to describe the mechanism of fusion: these include "the clamp" and the "provocateur" model of activation. By using biochemical and reverse genetics tools, we have obtained strong evidence in favor of the HN stalk-mediated activation of paramyxovirus fusion. Specifically, our data strongly support the notion that the short linker between the head and stalk plays a role in "conformational switching" of the head group to facilitate F-HN interaction and triggering.
副粘病毒科是一个由包膜的、负链、单链RNA病毒组成的大家族，对经济和公共卫生有重大影响。几乎所有副粘病毒的感染都是通过病毒与宿主细胞质膜以pH值无关的方式融合开始的。融合由受体结合蛋白血凝素神经氨酸酶（HN；根据病毒类型也称为H或G）蛋白和融合（F）蛋白协调，后者经历主要的重折叠过程以融合两个膜。关于受体结合与F激活偶联的机制细节尚未完全了解。在这里，我们确定连接庞大的酶活性头部和四螺旋束茎的柔性环区域对于促进融合至关重要。在副流感病毒5（PIV5）和新城疫病毒HN的该区域中脯氨酸替代消除了细胞-细胞融合，而HN保留受体结合和神经氨酸酶活性。通过使用反向遗传学，我们构建了在HN的头部-茎连接区域具有突变的重组PIV5-EGFP病毒。该区域的突变消除了病毒回收和感染性。总之，我们的数据表明环区域充当一个“铰链”，HN的庞大头部围绕其来回摆动以促进及时的HN介导的F触发，这一概念与副粘病毒融合的茎介导激活模型一致。
副粘病毒与宿主细胞质膜的融合对于病毒感染至关重要。膜融合通过受体结合蛋白（HN、H或G）与病毒融合糖蛋白（F）的相互作用来协调。已经提出了两种不同的模型来描述融合机制：这些包括“夹子”和激活的“刺激物”模型。通过使用生化和反向遗传学工具，我们获得了有力证据支持副粘病毒融合的HN茎介导激活。具体而言，我们的数据强烈支持这样的观点，即头部和茎之间的短连接子在头部基团的“构象转换”中起作用，以促进F-HN相互作用和触发。
