Processing of E1 and E2 glycoproteins of hepatitis C virus expressed in mammalian and insect cells

Processing of the envelope glycoproteins (E1 and E2) of hepatitis C virus (HCV) was investigated by using cDNA clones covering the structural and part of the nonstructural (NS) protein regions. The cDNA clones expressed in mammalian and insect cells were immunoprecipitated by serum of a hepatitis C patient and by monoclonal and polyclonal antibodies raised against the recombinant proteins expressed in insect cells or Escherichia coli. The E2 protein expressed in both insect and mammalian cells was a glycoprotein of 60 kDa (gp60) and removal of the sugar residues by N-glycanase yielded 38- and 40-kDa proteins. Pulse-chase experiments revealed that efficient expression and processing of the envelope proteins required coexpression with the flanking core and NS2 proteins. Not only E1 and E2 proteins but also NS2 and NS3 proteins were coprecipitated by anti-E1 or anti-E2 monoclonal antibody in the cells infected with the recombinant baculovirus expressing structural and NS proteins (NS2 and NS3), while only the NS3 protein was precipitated by anti-NS3 antibody. The association of E1 and E2 proteins was not influenced by the presence of a reducing agent and was still observed in the cells coinfected with the deletion mutants lacking both internal and C-terminal hydrophobic regions of each protein. Furthermore, the truncated forms of the E1 and E2 proteins were secreted into the culture supernatant and some of them were still associated with each other.