Secretion and purification of hepatitis C virus NS1 glycoprotein produced by recombinant baculovirus-infected insect cells

Recombinant baculoviruses that produce a putative non-structural protein 1 (NS1) of hepatitis C virus (HCV), predicted to be the second envelope glycoprotein, were constructed. The recombinant NS1 protein (re-NSI) produced in infected insect cells was localized on the cell surface and was apparently glycosylated, because it was susceptible to treatment with both tunicamycin and N-glycanase. Furthermore, re-NSI was effectively secreted into the culture supernatant when the putative NS1 signal peptide (SP) was replaced by the SP of rabies virus G protein, and the C-terminal hydrophobic region was eliminated. The secreted re-NSI was tagged with six His residues at the C terminus and purified simply by native Ni 2+-nitrilotriacetic acid (Ni 2+-NTA) affinity column chromatography. An enzyme-linked immunosorbent assay (ELISA) was developed for the serological diagnosis of HC using purified re-NSI. Anti-NSI antibody (Ab) was detected in 55 of 60 patients (92%) with chronic HC liver diseases. Thus, this ELISA for Ab directed against HCV re-NSI produced in insect cells is useful for the detection of chronic HC patients.