Cryo-EM structures of infectious bursal disease viruses with different virulences provide insights into their assembly and invasion  

传染性法氏囊病病毒不同毒力毒株的冷冻电镜结构帮助理解其组装和入侵机制

作　　者：Keyan Bao Xiaole Qi Yan Li Minqing Gong Xiaomei Wang Ping Zhu 包珂岩;祁小乐;李岩;龚敏卿;王笑梅;朱平(National Laboratory of Biomacromolecules,CAS Center for Excellence in Biomacromolecules,Institute of Biophysics,Chinese Academy of Sciences,Beijing 100101,China;Avian Immunosuppressive Diseases Division,State Key Laboratory of Veterinary Biotechnology,Harbin Veterinary Research Institute,Chinese Academy of Agricultural Sciences,Harbin 150069,China;OIE Reference Laboratory for Infectious Bursal Disease,Harbin Veterinary Research Institute,Chinese Academy of Agricultural Sciences,Harbin 150069,China;College of Life Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]National Laboratory of Biomacromolecules,CAS Center for Excellence in Biomacromolecules,Institute of Biophysics,Chinese Academy of Sciences,Beijing 100101,China [2]Avian Immunosuppressive Diseases Division,State Key Laboratory of Veterinary Biotechnology,Harbin Veterinary Research Institute,Chinese Academy of Agricultural Sciences,Harbin 150069,China [3]OIE Reference Laboratory for Infectious Bursal Disease,Harbin Veterinary Research Institute,Chinese Academy of Agricultural Sciences,Harbin 150069,China [4]College of Life Sciences,University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Science Bulletin》2022年第6期646-654,M0004,共10页科学通报（英文版）

基　　金：supported by the National Natural Science Foundation of China(U20A2061,31730023,31521002,32072852);the Chinese Ministry of Science and Technology(2017YFA0504700);the Chinese Academy of Sciences(CAS)(XDB37010100);the State Key Laboratory of Veterinary Biotechnology Foundation(SKLVBF201702);the National Laboratory of Biomacromolecules of China(2020KF12)。

摘　　要：Infectious bursal disease virus(IBDV)causes a highly contagious immunosuppressive disease in chickens,resulting in significant economic losses.The very virulent IBDV strain(vvIBDV)causes high mortality and cannot adapt to cell culture.In contrast,attenuated strains of IBDV are nonpathogenic to chickens and can replicate in cell culture.Although the crystal structure of T=1 subviral particles(SVP)has been reported,the structures of intact IBDV virions with different virulences remain elusive.Here,we determined the cryo-electron microscopy(cryo-EM)structures of the vvIBDV Gx strain and its attenuated IBDV strain Gt at resolutions of 3.3 Å and 3.2 Å,respectively.Compared with the structure of T=1 SVP,IBDV contains several conserved structural elements unique to the T=13 virion.Notably,the Nterminus of VP2,which is disordered in the SVP,interacts with the S_(F) strand of VP2 from its neighboring trimer,completing theβ-sheet of the S domain.This interaction helps to form a contact network by tethering the adjacent VP2 trimers and contributes to the assembly and stability of the IBDV virion.Structural comparison of the Gx and Gt strains indicates that H253 and T284 in the VP2 P domain of Gt,in contrast to Gx,form a hydrogen bond with a positively charged surface.This suggests that the combined mutations Q253 H/A284 T and the associated structural electrostatic features of the attenuated Gt strain may contribute to adaptation to cell culture.Furthermore,a negatively charged groove in VP2,containing an integrin binding IDA motif that is critical for virus attachment,was speculated to play a functional role in the entry of IBDV.传染性法氏囊病病毒(infectious bursal disease virus,IBDV)引起的传染性法氏囊病(infectious bursal disease,IBD)是鸡的一种高度传染性免疫抑制疾病,往往导致养禽业严重的经济损失.IBDV超强毒株(very virulent IBDV,vvIBDV)能引起鸡群的高致死率,不能适应体外细胞培养.相反,IBDV弱毒株对鸡不致病,能适应体外细胞培养.IBDV T=1亚病毒颗粒(sub-viral particles,SVP)的晶体结构已经被报道,但IBDV不同毒力毒株的全病毒结构尚未被解析,而这对于深入理解IBDV组装和入侵的分子机制非常重要.本研究利用冷冻电镜三维重构技术分别解析了传染性法氏囊病病毒vvIBDV Gx株和其致弱毒株Gt全病毒的3.3和3.2Å的高分辨率结构.与T=1 SVP相比,IBDV T=13全病毒呈现一些独特的、保守的结构特征,尤其是在SVP中呈现柔性的结构蛋白VP2的N末端,在T=13全病毒中与临近VP2三聚体S结构域的β束SF相互作用形成β折叠,这种相互作用将临近的VP2三聚体“拴”在一起,有助于病毒的组装和稳定.两种不同毒力毒株的结构比较发现,与vvIBDV Gx株相比,弱毒株Gt的VP2 P结构域的H254和T284之间形成氢键,并呈现正表面电势,这提示VP2的Q253H/A284T突变以及相应的表面电势的改变可能是Gt株适应体外细胞培养的重要机制.此外,VP2表面含有一个呈负表面电势的凹槽,该凹槽内含有在病毒结合细胞过程中发挥重要作用的整合素结合基序IDA,可能在IBDV的入侵过程中发挥重要作用.

关 键 词：Infectious bursal disease virus Very virulent strain Attenuated strain Cryo-EM structures 

分 类 号：S852.65[农业科学—基础兽医学]