HEPATITIS-C VIRUS E2 PROTEIN PURIFIED FROM MAMMALIAN-CELLS IS FREQUENTLY RECOGNIZED BY E2-SPECIFIC ANTIBODIES IN PATIENT SERA

The envelope protein of hepatitis C virus (HCV) is composed of two mem brane-associated glycoproteins, E1 and E2. To obtain HCV E2 protein as a secretory form at a high level, we constructed a recombinant chines e hamster ovary (CHO) cell line expressing a C-terminal truncated E2 ( E2t) fused to human growth hormone (hGH), CHO/hGHE2t. The hGHE2t fusio n protein was purified from the culture supernatant using anti-hGH mAb affinity chromatography at approximately 80% purity. The purified hGH E2t protein appeared to be assembled into oligomers linked by intermol ecular disulfide bond(s) when density gradient centrifugation and SDS- polyacrylamide gel electrophoresis were employed. When the purified fu sion protein was used for testing its ability to bind to antibodies sp ecific for HCV by enzyme-linked immunosorbent assay, the protein was r ecognized by antibodies in sera from 90% of HCV-positive patients. Tre atment of hGHE2t protein by beta-mercapto-ethanol, but not by heat and SDS, significantly reduced its reactivity to the antibodies of patien t sera, suggesting that intermolecular and/or intramolecular disulfide bonds are important for its ability to recognize its specific antibod y and that the E2 protein contains discontinuous antigenic epitope(s).