Structure-Function Dissection of Pseudorabies Virus Glycoprotein B Fusion Loops
Structure-Function Dissection of Pseudorabies Virus Glycoprotein B Fusion Loops
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DOI：
10.1128/jvi.01203-17
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发表时间：
2018-01-01
影响因子：
5.4
通讯作者：
Backovic, Marija
中科院分区：
文献类型：
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作者：
Vallbracht, Melina;Brun, Delphine;Backovic, Marija
糖蛋白B(GB)在疱疹病毒科中是保守的，负责推动病毒被膜与宿主细胞膜融合，在受体结合时进入并被病毒Gh/gl复合体激活。虽然已经报道了几种疱疹病毒gB胞外区的晶体结构，但膜融合机制仍然不清楚。在这里，我们报告了伪狂犬病病毒(PRV)gB胞外区的X射线结构，揭示了一个典型的III类融合后三聚体，它通过其融合环(FLS)以胆固醇依赖的方式与膜结合。FL残基的突变使我们能够剖析那些与脂双层不同亚区相互作用的区域及其在膜相互作用中的作用。我们测试了15 GB的变种与脂质体结合的能力，并在功能分析中进一步研究了它们的子集。我们发现PRV gB FL残基Trp187、Tyr192、Phe275和Tyr276对于脂质体结合以及细胞和病毒环境中的融合是必不可少的，它们在gB三聚体表面形成了一个连续的疏水斑块。结合其他甲型疱疹病毒GBS的研究结果，我们的数据建议了一种模型，在该模型中，Phe275从FL2末端向脂质双层的碳氢化合物核心深处伸出，而Trp187、Tyr192和Tyr276的侧链形成一个边缘，该边缘插入膜的更浅的界面区域，以催化融合过程。与贝塔病毒和伽马疱疹病毒的GBS的比较分析表明，这种膜相互作用模型适用于所有疱疹病毒的GBS。膜融合事件的中心是糖蛋白B(GB)，它是疱疹病毒家族中最保守的包膜蛋白。像其他病毒融合蛋白一样，gB通过两个称为融合环(FLS)的多肽片段将自己锚定在靶膜上。关于GB FLS如何插入到脂质双层中的分子细节还没有描述。在这里，我们提供了伪狂犬病病毒Gb关键FL残基的结构和功能数据，这使我们能够首次提出一个分子模型来理解所有疱疹病毒GBS与靶膜的初始相互作用是如何建立的。
Conserved across the family Herpesviridae, glycoprotein B (gB) is responsible for driving fusion of the viral envelope with the host cell membrane for entry upon receptor binding and activation by the viral gH/gL complex. Although crystal structures of the gB ectodomains of several herpesviruses have been reported, the membrane fusion mechanism has remained elusive. Here, we report the X-ray structure of the pseudorabies virus (PrV) gB ectodomain, revealing a typical class III postfusion trimer that binds membranes via its fusion loops (FLs) in a cholesterol-dependent manner. Mutagenesis of FL residues allowed us to dissect those interacting with distinct subregions of the lipid bilayer and their roles in membrane interactions. We tested 15 gB variants for the ability to bind to liposomes and further investigated a subset of them in functional assays. We found that PrV gB FL residues Trp187, Tyr192, Phe275, and Tyr276, which were essential for liposome binding and for fusion in cellular and viral contexts, form a continuous hydrophobic patch at the gB trimer surface. Together with results reported for other alphaherpesvirus gBs, our data suggest a model in which Phe275 from the tip of FL2 protrudes deeper into the hydrocarbon core of the lipid bilayer, while the side chains of Trp187, Tyr192, and Tyr276 form a rim that inserts into the more superficial interfacial region of the membrane to catalyze the fusion process. Comparative analysis with gBs from beta-and gammaherpesviruses suggests that this membrane interaction model is valid for gBs from all herpesviruses.IMPORTANCE Herpesviruses are common human and animal pathogens that infect cells by entering via fusion of viral and cellular membranes. Central to the membrane fusion event is glycoprotein B (gB), which is the most conserved envelope protein across the herpesvirus family. Like other viral fusion proteins, gB anchors itself in the target membrane via two polypeptide segments called fusion loops (FLs). The molecular details of how gB FLs insert into the lipid bilayer have not been described. Here, we provide structural and functional data regarding key FL residues of gB from pseudorabies virus, a porcine herpesvirus of veterinary concern, which allows us to propose, for the first time, a molecular model to understand how the initial interactions by gBs from all herpesviruses with target membranes are established.