Purification of a soluble hepatitis E open reading frame 2-derived protein with unique antigenic properties.

The second open reading frame (ORF2) of hepatitis E virus (HEV) is predicted to encode a 73-kDa capsid protein (1). When full-length ORF2 was expressed in insect cells (Spodoptera frugiperda (Sf9)) using a recombinant baculovirus, two distinct HEV polypeptides were observed: a full-length insoluble 73-kDa protein, and a soluble 56.5-kDa protein. Following purification and sequence analysis, it was determined that the 56.5-kDa protein was derived from endoproteolytic cleavage site that was between the Thr and Ala residues located at amino acids 111 and 112 in the ORF2 sequence with the carboxy terminus corresponding to residue 636 of the ORF2 sequence. Comparative ELISA data using human acute-phase antisera demonstrated that the 56.5-kDa protein served as a highly reactive antigen in detecting anti-HEV antibodies. These data suggest that the 56.5-kDa protein may serve as a particularly useful antigen for both diagnostic and vaccine purposes.