Removal of a N-linked glycosylation site of classical swine fever virus strain Brescia Erns glycoprotein affects virulence in swine

Erns glycoprotein, along with E1 and E2, is one of the three envelope glycoproteins of classical swine fever virus (CSFV). Erns is a heavily glycosylated protein involved in several functions, including virus attachment and entry to target cells, production of neutralizing antibodies, and virulence. The role of added glycans to CSFV strain Brescia Erns on virus virulence was assessed in swine. A panel of virus mutants was constructed and used to investigate whether the removal of each of seven putative glycosylation sites in the Erns glycoprotein would affect viral virulence in swine. Only N269A/Q substitution rendered attenuated viruses (N1v/N1Qv) that, unlike BICv and other mutants, produced a transient infection in swine characterized by mild symptoms and decreased virus shedding. Notably, N1v efficiently protected swine from challenge with virulent BICv at 3 and 21 days post-infection suggesting that glycosylation of Erns could be modified for development of CSF live-attenuated vaccines.