INVOLVEMENT OF ENDOPLASMIC-RETICULUM CHAPERONES IN THE FOLDING OF HEPATITIS-C VIRUS GLYCOPROTEINS

The hepatitis C virus (HCV) genome encodes two envelope glycoproteins (El and E2) which interact noncovalently to form a heterodimer (E1-E2) . During the folding and assembly of HCV glycoproteins, a large portio n of these proteins are trapped in aggregates, reducing the efficiency of native E1-E2 complex assembly. To better understand this phenomeno n and to try to increase the efficiency of HCV glycoprotein folding, e ndoplasmic reticulum chaperones potentially interacting with these pro teins were studied. Calnexin, calreticulin, and BiP were shown to inte ract with El and E2, whereas no interaction was detected between GRP94 and HCV glycoproteins. The association of HCV glycoproteins with caln exin and calreticulin was faster than with BiP, and the kinetics of in teraction with calnexin and calreticulin were very similar. However, c alreticulin and BiP interacted preferentially with aggregates whereas calnexin preferentially associated with monomeric forms of HCV glycopr oteins or noncovalent complexes. Tunicamycin treatment inhibited the b inding of HCV glycoproteins to calnexin and calreticulin, indicating t he importance of N-linked oligosaccharides for these interactions. The effect of the co-overexpression of each chaperone on the folding of H CV glycoproteins was also analyzed. However, the levels of native E1-E 2 complexes were not increased. Together, our data suggest that calnex in plays a role in the productive folding of HCV glycoproteins whereas calreticulin and BiP are probably involved in a nonproductive pathway of folding.