Dimerisation of glycoprotein Erns of classical swine fever virus is not essential for viral replication and infection.

The pestivirus glycoprotein E^rns, a ribonuclease, is expressed on the surface of virions and in infected cells as a disulfide-linked homodimer. E^rns is involved in the infection process and its RNase activity is probably involved in viral replication and pathogenesis. The most C-terminal cysteine residue forms an intermolecular disulfide bond with another E^rns monomer, resulting in an E^rns dimer. To study the function of dimerisation of E^rns for viral replication, the cysteine residue at amino acid position 438 was mutated into a serine residue. The mutated C438S gene was cloned into a vector containing an infectious cDNA copy of the CSFV C-strain genome. Using reverse genetics, a mutant virus was generated that only expressed monomeric E^rns, confirming that Cys 438 is essential for homodimerisation. Characterization of this mutant virus and of a baculovirus-expressed C438S mutant protein indicated that the loss of the dimeric state of E^rns reduced the affinity of binding of virions and E^rns to heparan sulphate (HS), the receptor for E^rns on the cell surface of SK6 cells. This suggests that interaction of virus-bound E^rns homodimers with membrane associated HS may be a joined action of the two HS-binding domains (one in each monomer) present in the homodimer. [ABSTRACT FROM AUTHOR]