The small envelope protein of porcine reproductive and respiratory syndrome virus possesses ion channel protein-like properties.
The small envelope (E) protein of porcine reproductive and respiratory syndrome virus (PRRSV) is a hydrophobic 73 amino acid protein encoded in the internal open reading frame (ORF) of the bicistronic mRNA2. As a first step towards understanding the biological role of E protein during PRRSV replication, E gene expression was blocked in a full-length infectious clone by mutating the ATG translational initiation to GTG, such that the full-length mutant genomic clone was unable to synthesize the E protein. DNA transfection of PRRSV-susceptible cells with the E gene knocked-out genomic clone showed the absence of virus infectivity. P129-DeltaE-transfected cells however produced virion particles in the culture supernatant, and these particles contained viral genomic RNA, demonstrating that the E protein is essential for PRRSV infection but dispensable for virion assembly. Electron microscopy suggests that the P129-DeltaE virions assembled in the absence of E had a similar appearance to the wild-type particles. Strand-specific RT-PCR demonstrated that the E protein-negative, non-infectious P129-DeltaE virus particles were able to enter cells but further steps of replication were interrupted. The entry of PRRSV has been suggested to be via receptor-mediated endocytosis, and lysomotropic basic compounds and known ion-channel blocking agents both inhibited PRRSV replication effectively during the uncoating process. The expression of E protein in Escherichia coli-mediated cell growth arrests and increased the membrane permeability. Cross-linking experiments in cells infected with PRRSV or transfected with E gene showed that the E protein was able to form homo-oligomers. Taken together, our data suggest that the PRRSV E protein is likely an ion-channel protein embedded in the viral envelope and facilitates uncoating of virus and release of the genome in the cytoplasm.
Lee
Changhee
C
Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Yoo
Dongwan
D
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D017353:Gene Deletion; D005814:Genes, Viral; D006801:Humans; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D019316:Porcine respiratory and reproductive syndrome virus / Q000235:genetics / Q000502:physiology*; D012367:RNA, Viral / Q000032:analysis; D014759:Viral Envelope Proteins / Q000235:genetics / Q000502:physiology*; D014771:Virion / Q000648:ultrastructure; D019065:Virus Assembly; D053586:Virus Internalization; D014779:Virus Replication
D002121:Calcium Channel Blockers; D012367:RNA, Viral; D014759:Viral Envelope Proteins