Comparison of secretion of a hepatitis C virus glycoprotein in Saccharomyces cerevisiae and Kluyveromyces lactis.

A C-terminally truncated form of the hepatitis C virus (HCV) putative envelope glycoprotein E2 was expressed in two yeast species, Saccharomyces cerevisiae and Kluyveromyces lactis, using a yeast signal peptide sequence to direct the viral glycoprotein to the endoplasmic reticulum (ER) pathway of secretion. Characterization of secreted E2 showed that the protein is endoglycosidase-H-sensitive in both yeasts. Moreover, in vivo inhibition of glycosylation with tunicamycin prevented secretion of E2 and showed that, of its 11 putative N-linked glycosylation sites, at least eight were core-glycosylated. Analysis of the heterologous glycoprotein by SDS-PAGE under nonreducing conditions and by gel filtration demonstrated the formation of multiple disulphides, which resulted in secretion of heterogeneous aggregates with an average molecular mass of 770-1000 kDa in both yeasts. However, variations were observed in the binding of the glycoprotein secreted by the two yeasts to a mannose-specific lectin, and also in its reactivity with anti-E2-specific antibodies. This denotes differences between the two yeasts in folding and/or modification of the E2 glycoprotein.