Structure-antigenicity relationship of peptides from the pre-S2 region of the hepatitis B virus surface antigen

Peptide antigenicity against the pre-S2 region of the hepatitis B virus surface antigen was studied using a pre-S2 specific anti-hepatitis B virus mouse monoclonal antibody (H8 mAb) and synthetic peptides by competitive ELISA. The mAb showed preferences for long peptides with the sequence 120/123-145, though the mAb binding region was located in the sequence 130-145 from the analysis of a conjugation study. The N-terminal residues 120/123-129 play an important role for the maintenance of the highly antigenic structure of the B cell epitope. Among these, the N-terminal hydrophilic residues 124-126 and hydrophobic residue 127 were important, whereas residues 120-122 did not affect antigenicity. Residues 131 and 141 appeared to be critical for the mAb binding. The relationship between peptide structure and antigenicity was also investigated by probing the secondary structure of the peptides by circular dichroism. Highly antigenic peptides elicited more ordered structure in 20% trifluoroethanol than less antigenic peptides. The results suggested that peptide antigenicities against H8 mAb are closely related to the B-cell epitope conformations of peptides.ope