CHARACTERIZATION OF TRUNCATED FORMS OF HEPATITIS-C VIRUS GLYCOPROTEINS

Hepatitis C virus (HCV) glycoproteins (E1 and E2) both contain a carbo xy-terminal hydrophobic region, which presumably serves as a membrane anchor, When they are expressed in animal cell cultures, these glycopr oteins, in both mature complexes and misfolded aggregates, are retaine d in the endoplasmic reticulum, The effect of carboxyterminal deletion s on HCV glycoprotein secretion and folding was examined in this study . Sindbis and/or vaccinia virus recombinants expressing truncated form s of these glycoproteins ending at amino acids 311, 330, 354 and 360 ( truncated E1), and 661, 688, 704 and 715 (truncated E2) were construct ed, When expressed using Sindbis virus vectors, only truncated forms o f E1 and E2 ending at amino acids 311 (E1(t311)) and 661 (E2(t661)), r espectively, were efficiently secreted. Analysis of secretion of trunc ated forms of E2 glycoprotein expressed by vaccinia viruses indicated that significant secretion was still observed for a protein as large a s E2(t715). However, only secreted E2(t661) appeared to be properly fo lded, Secreted HCV glycoprotein complexes were also detected in the su pernatant of cell culture when E1(t311) and E2(t661) were coexpressed. Nevertheless, these secreted complexes, as well as E1(t311) expressed alone, were misfolded. The effect of coexpression of E1 and E2 glycop roteins on each other's folding was evaluated with the help of a confo rmation-sensitive monoclonal antibody (for E2) or by analysing intramo lecular disulfide bond formation (for E1). Our data indicate that the folding of E2 is independent of E1, but that E2 is required for the pr oper folding of E1.