This invention provides a novel mammalian expression system that is capable of generating high levels of expressed hepatitis C virus (HCV) proteins which have previously proved difficult to express due to their non-secretory properties. In particular, the invention provides a plasmid for the expression of the HCV second envelope protein (E2) designated p577. This plasmid encodes a recombinant protein comprising the immunoglobulin signal peptide and amino acids 388-664 of the HCV E2 glycoprotein. This unique expression system produces high levels of HCV proteins that are properly processed, glycosylated, and folded.