title: Structure-based mutational analysis of several sites in the E protein: implications for understanding the entry mechanism of Japanese encephalitis virus.
abstract: Japanese encephalitis virus (JEV), which causes viral encephalitis in humans, is a serious risk to global public health. The JEV envelope protein mediates the viral entry pathway, including receptor-binding and low-pH-triggered membrane fusion. Utilizing mutagenesis of a JEV infectious cDNA clone, mutations were introduced into the potential receptor-binding motif or into residues critical for membrane fusion in the envelope protein to systematically investigate the JEV entry mechanism. We conducted experiments evaluating infectious particle, recombinant viral particle, and virus-like particle production and found that most mutations impaired virus production. Subcellular fractionation confirmed that five mutations--in I0, ij, BC, and FG and the R9A substitution-impaired virus assembly, and the assembled virus particles of another five mutations--in kl and the E373A, F407A, L221S, and W217A substitutions--were not released into the secretory pathway. Next, we examined the entry activity of six mutations yielding infectious virus. The results showed N154 and the DE loop are not the only or major receptor-binding motifs for JEV entry into BHK-21 cells; four residues, H144, H319, T410, and Q258, participating in the domain I (DI)-DIII interaction or zippering reaction are important to maintain the efficiency of viral membrane fusion. By continuous passaging of mutants, adaptive mutations from negatively charged amino acids to positively charged or neutral amino acids, such as E138K and D389G, were selected and could restore the viral entry activity.
  
  
  OBJECTIVE
  Recently, there has been much interest in the entry mechanism of flaviviruses into host cells, including the viral entry pathway and membrane fusion mechanism. Our study provides strong evidence for the critical role of several residues in the envelope protein in the assembly, release, and entry of JEV, which also contributes to our understanding of the flaviviral entry mechanism. Furthermore, we demonstrate that the H144A, H319A, T410A, and Q258A mutants exhibit attenuated fusion competence, which may be used to develop novel vaccine candidates for flaviviruses.
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Haibin
authors.initials: H
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Shaobo
authors.initials: S
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Xiangyang
authors.initials: X
authors.lastname: Zu
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, People's Republic of China xiaogf@wh.iov.cn.
authors.forename: Gengfu
authors.initials: G
authors.lastname: Xiao
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D006224:Cricetinae; D004252:DNA Mutational Analysis; D004279:DNA, Viral / Q000235:genetics; D018349:Encephalitis Viruses, Japanese / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D004672:Encephalitis, Japanese / Q000821:virology; D005814:Genes, Viral; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000235:genetics*; D053586:Virus Internalization; D014779:Virus Replication
chemical_list: D004279:DNA, Viral; D014759:Viral Envelope Proteins