HEPATITIS-C VIRUS GLYCOPROTEIN FOLDING - DISULFIDE BOND FORMATION ANDASSOCIATION WITH CALNEXIN

The hepatitis C virus (HCV) glycoproteins (E1 and E2) are released fro m the polyprotein by signal peptidase-mediated cleavage and interact t o form a heterodimer. Since properly folded subunits are usually requi red for specific recognition and stable oligomer formation, the rate o f stable E1E2 complex formation, which is low, may be limited by the r ate of HCV E1 and/or E2 folding. In this study, the folding of the HCV E1 and E2 glycoproteins was monitored by observing the kinetics of in tramolecular disulfide bond formation. The association/dissociation of E1 and E2 with calnexin was also examined, since this molecular chape rone appears to play a major role in quality control via retention of incompletely folded or misfolded proteins in the endoplasmic reticulum . Our results indicate that the disulfide-dependent folding of E2 occu rs rapidly and appears to be complete upon cleavage of the precursor E 2-NS2. In contrast, folding of E1 is slow (>1 h), suggesting that this step may be rate limiting for E1E2 oligomerization. Both HCV glycopro teins associated rapidly with calnexin, but dissociation was slow, con sistent with the slow folding and assembly of E1E2 glycoprotein comple xes. These results suggest a role for prolonged association with calne xin in the folding and assembly of HCV glycoprotein heterodimer comple xes.