PLOS Pathogens:中科院微生物所高福研究组等揭示伪狂犬病毒囊膜糖

2017年5月19日，国际微生物学知名期刊《PLOS Pathogens》在线发表了中国科学院微生物研究所高福团队、严景华课题组和广西大学罗廷荣教授研究组合作的一篇研究论文，研究揭示伪狂犬病毒囊膜糖蛋白gD识别受体nectin-1的分子机制。博士生李安、四川大学教授逯光文为共享第一作者，高福、严景华和罗廷荣教授为论文共同通讯作者。

疱疹病毒膜融合需要多个病毒蛋白与多个细胞表面受体参与，相互协调才能完成，整个过程极其复杂。病毒表面糖蛋白D (gD)与宿主细胞受体的识别是α-疱疹病毒感染初期的必不可少的步骤。在迄今已鉴定的gD受体中，细胞黏附分子nectin-1参与了多种α-疱疹病毒入侵宿主细胞的过程，被认为是最有效的gD受体。因此，gD识别nectin-1的分子机制成为α-疱疹病毒研究领域的一个重要科学问题。

在前期研究中已经解析了I和II型单纯疱疹病毒(HSV)gD与其受体nectin-1的复合物结构，发现HSV gD蛋白结合于nectin-1分子二聚化的接触面上。这一结合模式破坏了nectin-1自身的二聚化，进而削弱了细胞粘附，有利于病毒入侵(Nature Communications 2011;Journal of Virology 2014)。同时还阐明了HSV病毒另一关键糖蛋白gB与受体PILRa相互作用机制(PNAS 2014)。

猪伪狂犬病病毒(Pseudorabies virus, PRV)与HSV同属 α 疱疹病毒。HSV 是Simplexvirus 属成员，而PRV是Varicellovirus 病毒属成员。有研究表明PRV同样可以利用nectin-1作为受体，然而其分子机制不清楚。另外，PRV感染宿主是猪，那么它能否结合HSV的受体，如人源nectin-1、HVEM等，进而存在感染人的风险呢?

团队系统地研究了PRV gD与nectin-1的相互作用，证明了PRV可以感染人源和猪源nectin-1过表达的细胞，并且PRV gD对两种来源的nectin-1亲和力基本相同，这警示人们要防范PRV感染人的风险。研究进一步解析了PRV gD胞外域及其与nectin-1复合体晶体结构。结构显示PRV gD的空间结构与HSV非常相似，尽管其序列同源性只有22%，与HSV gD结构不同的是，PRV gD N-末端的loop区比较短，而这个区域正好是HSV gD结合另一个受体HVEM的位置，这也就解释了为什么PRV不能用HVEM做受体的机制。复合体结构表明PRV gD以与HSV相同的模式结合nectin-1，然而，在PRV gD与nectin-1结合界面处有多个独有的特征，这些特征促使PRV配体利用不同于HSV gD的氨基酸残基与nectin-1相互作用。该项研究不仅揭示了PRV gD与nectin-1的相互作用分子机制，而且丰富了人们对α-疱疹病毒亚科的受体结合模式的理解，也会为开发抑制伪狂犬病毒融合的小分子药物奠定理论基础。

原文链接：

Structural basis of nectin-1 recognition by pseudorABIes virus glycoprotein D

原文摘要：

An early and yet indispensable step in the alphaherpesvirus infection is the engagement of host receptors by the viral envelope glycoprotein D (gD). Of the thus-far identified gD receptors, nectin-1 is likely the most effective in terms of its wide usage by multiple alphaherpesviruses for cell entry. The molecular basis of nectin-1 recognition by the gD protein is therefore an interesting scientific question in the alphaherpesvirus field. Previous studies focused on the herpes simplex virus (HSV) of the Simplexvirus genus, for which both the free gD structure and the gD/nectin-1 complex structure were reported at high resolutions. The structural and functional features of other alphaherpesviral gDs, however, remain poorly characterized. In the current study, we systematically studied the characteristics of nectin-1 binding by the gD of aVaricellovirus genus member, the pseudorabies virus (PRV). We first showed that PRV infects host cells via both human and swine nectin-1, and that its gD exhibits similar binding affinities for nectin-1 of the two species. Furthermore, we demonstrated that removal of the PRV gD membrane-proximal residues could significantly increase its affinity for the receptor binding. The structures of PRV gD in the free and the nectin-1-bound states were then solved, revealing a similar overall 3D fold as well as a homologous nectin-1 binding mode to its HSV counterpart. However, several unique features were observed at the binding interface of PRV gD, enabling the viral ligand to utilize different gD residues (from those of HSV) for nectin-1 engagement. These observed binding characteristics were further verified by the mutagenesis study using the key-residue mutants of nectin-1. The structural and functional data obtained in this study, therefore, provide the basis of receptor recognition by PRV gD.

doi:10.1371/journal.ppat.1006314

作者：高福