Identification of the glycosaminoglycan-binding site on the glycoprotein Erns of bovine viral diarrhoea virus by site-directed mutagenesis

Bovine viral diarrhoea virus (BVDV) envelope glycoprotein E-rns interacts with highly sulphated heparin-like glycosaminoglycans (GAGs) located on the cell surface as an early step in virus infection of cells. Site-directed mutagenesis of recombinant E-rns was undertaken and analysis of mutants by heparin-affinity chromatography and cell surface binding showed that a cluster of basic amino acids ((KKLENKSK487)-K-480) near the C terminus of E-rns was essential for binding. Mutants with amino acid substitutions of lysine residues 481 and 485 in Ems reduced the binding of E-rns to immobilized heparin and cellular GAGs but retained ribonuclease activity. In contrast to normal E-rns, E-rns that was unable to bind to cells also failed to inhibit BVDV infection of cells when the cells were pre-incubated with E-rns. It is proposed that the cluster of basic residues ((KKLENKSK487)-K-480.) localized at the C-terminal end of E-rns constitutes a GAG-binding site.