Evaluation of the N-terminal role in peptide antigenicity of the preS2 region of the hepatitis B virus surface antigen

Previously we reported that the N-terminal sequence 120-129 of the preS2 region of the hepatitis B virus (HBV) surface antigen (HBsAg) plays an important role in peptide antigenicity against an preS2 specific anti-HBsAg monoclonal antibody (H8 mAb) by affecting the B cell epitope conformation of a peptide existing within the sequence 130-145. In this study, we tried to confirm the previous results using a series of N-terminal sequentially deleted peptides and peptides substituted at position 127. This position was previously found to be important for H8 mAb binding. Peptide antigenicity of sequentially deleted peptides was gradually decreased when the residues from 125 to 129 were deleted, indicating that the residues cumulatively affect antigenicity. Peptide antigenicity relative to the substituted residues at position 127 of p123 showed an order of F>I>E≥T>A≥ P>K and was correlated with their CD spectra. Structure-dependent peptide antigenicity was also found in many polyclonal antisera produced by immunization with peptide-protein conjugates and HBsAg. Twenty-nine out of 34 polyclonal antisera had reactivities increased 2-fold or more with p123 relative to those with p130. Among them, 10 antisera showed increased reactivities of 7 fold or more. These results confirm our previous results, which suggested the existence of the conformational B cell epitope in the preS2 region maintained by the N-terminal sequence. This experiment also suggests that N-terminal sequence 125-129 is important in maintaining a higher antigenic structure.ope