Hepatitis C virus envelope glycoprotein E1 originates in the endoplasmic reticulum and requires cytoplasmic processing for presentation by class I MHC molecules

We investigated whether hepatitis: C virus envelope glycoprotein E1 is tran sported from the endoplasmic reticulum (ER) to the cytoplasm of infected ce lls for class I MHC processing. Target cells expressing E1 were killed by C TL lines from a hepatitis C virus-infected chimpanzee, and synthetic peptid es were used to define an epitope (amino acids 233-GNASRCWVA-241) presented by the Patr-B*1601 class I MHC molecule. An unusually high concentration ( >100 nM) of this nonameric peptide was required for target cell lysis, but this could de reduced at least 1000-fold hy replacing the asparagine at ami no acid position 234 (Asn(234)) with aspartic acid (Asp), the anticipated a nchor residue for NH2-terminal peptide binding to Patr-B*1601, Conspicuousl y, position 234 is part of an N-glycosylation motif (Asn-Xaa-Ser/Thr), sugg esting that the Asn(234) to Asp substitution might occur naturally within t he cell due to deglycosylation/deamidation of this amino acid by the cytoso lic enzyme peptide N-glycanase. In support of this model, we demonstrate th at presentation of the epitope depended on 1) cotranslational synthesis of E1 in the ER, 2) glycosylation of the E1 molecule, and 3) a functional TAP transporter to shuttle peptide from the cytosolic to ER compartment. These results indicate for the first time that during infection of the host, vira l envelope glycoproteins originating in the ER are processed in the cytopla sm for class I MHC presentation. That a posttranslational change in amino a cid sequence from Asn to Asp alters the repertoire of peptides presented to CD8(+) CTL has implications for the design of antiviral vaccines.