Interactions of bovine viral diarrhoea virus glycoprotein Erns with cell surface glycosaminoglycans

Recombinant Erns glycoprotein of bovine viral diarrhoea virus (BVDV) has been tagged with a marker epitope or linked to an immunoglobulin Fc tail and expressed in insect and mammalian cell lines. The product was shown to be functional, both having ribonuclease activity and binding to a variety of cells that were permissive and non-permissive for replication of BVDV. Addition of soluble Erns to the medium blocked replication of BVDV in permissive cells. Binding of epitope-tagged Erns to permissive calf testes (CTe) cells was abolished and virus infection was reduced when cells were treated with heparinases I or III. Erns failed to bind to mutant Chinese hamster ovary (CHO) cells that lacked glycosaminoglycans (pgsA-745 cells) or heparan sulphate (pgsD-677 cells) but bound to normal CHO cells. Erns also bound to heparin immobilized on agarose and could be eluted by heparin and by a high concentration of salt. Flow cytometric analysis of Erns binding to CTe cell cultures showed that glycosaminoglycans such as heparin, fucoidan and dermatan sulphate all inhibit binding but dextran sulphate, keratan sulphate, chondroitin sulphate and mannan fail to inhibit binding. The low molecular mass polysulphonated inhibitor suramin also inhibited binding to CTe cells but poly-l-lysine did not. Furthermore, suramin, the suramin analogue CPD14, fucoidan and pentosan polysulphate inhibited the infectivity of virus. It is proposed that binding of Erns to cells is through an interaction with glycosaminoglycans and that BVDV may bind to cells initially through this interaction.