Glycosylation of the Hepatitis C Virus Envelope Protein E1 Is Dependent on the Presence of a Downstream Sequence on the Viral Polyprotein

Jean Dubuisson,Sandrine Duvet,Jean-Christophe Meunier,Anne Op De Beeck,Rene Cacan,Czeslaw Wychowski,Laurence Cocquerel

doi:10.1074/jbc.m004326200

Abstract

The addition of N-linked oligosaccharides to Asn-X-(Ser/Thr) sites is catalyzed by the oligosaccharyltransferase, an enzyme closely associated with the translocon and generally thought to have access only to nascent chains as they emerge from the ribosome. However, the presence of the sequon does not automatically ensure core glycosylation because many proteins contain sequons that remain either nonglycosylated or glycosylated to a variable extent. 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, E1 and E2, were released from a polyprotein precursor after cleavage by host signal peptidase(s). When expressed alone, E1 was not efficiently glycosylated. However, E1 glycosylation was improved when expressed as a polyprotein including full-length or truncated forms of E2. These data indicate that glycosylation of E1 is dependent on the presence of polypeptide sequences located downstream of E1 on HCV polyprotein.

Highlights

Proteins that are transported and sorted by the secretory pathway begin their journey at the endoplasmic reticulum (ER)1 membrane
A hydrophobic sequence present in the second half of the transmembrane domain of E1 is the signal sequence for the other envelope protein E2 located immediately downstream of E1 on the polyprotein
When deglycosylated by endo␤-N-acetylglucosaminidase H or Peptide:N-glycosidase F (PNGase F), E1 was resolved as a single fast migrating band (Fig. 2b), which comigrated with E1 expressed in cells treated by tunicamycin, a drug that blocks core glycosylation of nascent glycoprotein precursors

Summary

Introduction

Proteins that are transported and sorted by the secretory pathway begin their journey at the endoplasmic reticulum (ER)1 membrane. These data indicate that glycosylation of E1 is dependent on the presence of polypeptide sequences located downstream of E1 on HCV polyprotein.

Results

Conclusion