N-terminal domain of Borna disease virus G (p56) protein is sufficient for virus receptor recognition and cell entry

Borna disease virus (BDV) surface glycoprotein (GP) (p56) has a predicted molecular mass of 56 kDa. Due to extensive posttranslational glycosylation the protein migrates as a polypeptide of 84 kDa (gp84). The processing of gp84 by the cellular protease furin generates gp43, which corresponds to the C-terminal part of gp84. Both gp84 and gp43 have been implicated in viral entry involving receptor-mediated endocytosis and pH-dependent fusion. We have investigated the domains of BDV p56 involved in virus entry. For this, we used a pseudotype approach based on a recently developed recombinant vesicular stomatitis virus (VSV) in which the gene for green fluorescent protein was substituted for the VSV G protein gene (VSV Delta G*). Complementation of VSV Delta G* with BDV p56 resulted in infectious VSV Delta G* pseudotypes that contained both BDV gp84 and gp43. BDV-VSV chimeric GPs that contained the N-terminal 244 amino acids of BDV p56 and amino acids 421 to 511 of VSV G protein were efficiently incorporated into VSV Delta G* particles, and the resulting pseudotype virions were neutralized by BDV-specific antiserum. These findings indicate that the N-terminal part of BDV p56 is sufficient for receptor recognition and virus entry.