Epitope mapping of preS2 of the hepatitis B virus surface antigen against a conformation-dependent monoclonal antibody using synthetic peptides

Previously we reported that the N-terminal sequence 120/123-129 of the preS2 region of the hepatitis B virus surface antigen plays an important role on peptide antigenicity against a monoclonal antibody H8 (H8 mAb) by affecting the B cell epitope conformation of a peptide existing within the sequence 130-145. In this study, we try to map the H8 mAb binding site using a series of substituted peptides in the sequence 131-143 by competitive ELISA. Peptide antigenicities were greatly reduced when the residues 131 (L), 137 (R), 140 (Y), 141 (F) and 142 (P) were substituted. The residues 133 (D), 134 (P) and 136 (V) had a slight affect on the mAb binding, whereas the residues 135 (R) and 139 (L) had no effects on the mAb binding. In contrast to H8 mAb, however, three anti-HBsAg polyclonal antisera showed the lowest bindings to the peptide substituted at position 135. These results suggest that the epitope against H8 mAb is discontinuously conformational.ope