Characterisation of a linear binding site for a monoclonal antibody to hepatitis B core antigen

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Abstract
The complete amino acid (aa) sequence of the hepatitis B virus (HBV) core protein (HBcAg), ayw subtype, was synthesized as decapeptides with five overlapping aas. The peptides were tested for reactivity with monoclonal antibodies (mAbs) to HBcAg (35/312, 37/275, and 7/275). All the mAbs specifically inhibited human anti‐HBc by cross competition in assays for anti‐HBc and anti‐HBe.The mAb 35/312 recognised a peptide covering residues 76–85 of the HBcAg sequence. The other two mAbs did not react specifically with any linear peptide, suggesting discontinuous epitopes for these mAbs. The linear sequence EDPASR at residues 77–82 was found to constitute the epitope for mAb 35/312 when fine mapping the binding site. The most essential aas for mAb 35/312 were found to be the DP at residues 79–80, when peptides were synthesized where the aas at 77–83, were substituted by the other 19 aas. Since the mAb 35/312 inhibits the binding of human anti‐HBc positive sera, which are known to recognise an SDS labile epitope, the sequence 77–82 might be a part of a larger discontinuous epitope. Alternatively the mAb 35/312 blocks the binding of human anti‐HBc by steric hindrance.