DISCONTINUOUS EPITOPES OF HEPATITIS-B SURFACE-ANTIGEN DERIVED FROM A FILAMENTOUS PHAGE PEPTIDE LIBRARY

The structure of the small hepatitis B virus surface antigen (HBsAg) w as investigated by epitope mapping of four anti-HBsAg monoclonal antib odies (mAbs). Amino acid sequences of epitopes were derived from affin ity-enrichment experiments (biopanning) using a filamentous phage pept ide library. The library consists of 10(9) different clones bearing a 30-residue peptide fused to gene III. Sequence homologies between pept ides obtained from panning the library against the antibodies and the native HBsAg sequence allowed for precise description of the binding r egions. Three of four mAbs were found to bind to distinct discontinuou s epitopes between amino acid residues 101 and 207 of HBsAg. The fourt h mAb was demonstrated to bind to residues 121-124. The sequence data are supported by ELISA assays demonstrating the binding of the HBsAg-s pecific peptides on filamentous phage to mAbs. The sequence data were used to map the surface of HBsAg and to derive a topological model for the cy-carbon trace of the 101-207 region of HBsAg. The approach shou ld be useful for other proteins for which the crystal structure is not available but a representative set of mAbs can be obtained.