Glycosylation of the hepatitis C virus envelope protein E1 is dependent onthe presence of a downstream sequence on the viral polyprotein

The addition of N-linked oligosaccharides to Asn-X-(Ser/Thr) sites is catal yzed by the oligosaccharyltransferase, an enzyme closely associated with th e translocon and generally thought to have access only to nascent chains as they emerge from the ribosome. However, the presence of the sequon does no t automatically ensure core glycosylation because many proteins contain seq uons that remain either nonglycosylated or glycosylated to a variable exten t. In this study, hepatitis C virus (HCV) envelope protein E1 was used as a model to study the efficiency of N-glycosylation. HCV envelope proteins, E 1 and E2, were released from a polyprotein precursor after cleavage by host signal peptidase(s). When expressed alone, E1 was not efficiently glycosyl ated. However, E1 glycosylation was improved when expressed as a polyprotei n including full-length or truncated forms of E2. These data indicate that glycosylation of E1 is dependent on the presence of polypeptide sequences l ocated downstream of E1 on HCV polyprotein.