Identification of an epitope region of the human proliferation-associated nucleolar antigen P120

An epitope region, located at amino acid residues 173-180 (EAAA-GIQW), of a human cell proliferation-associated nucleolar antigen, P120, has been defined by mutational analysis and competition assays. A synthetic peptide corresponding to this epitope region completely blocks the binding of the anti-P120 antibody to Escherichia coli-expressed P120 and the HeLa nucleolar P120 protein. Adjacent peptides lack inhibitory effects. The antigenic site includes a hydrophilic residue and a hydrophobic stretch. The glutamyl and tryptophanyl residues in this region make major contributions to the binding of P120 to its antibody, since peptides lacking either the glutamyl or the tryptophanyl residue do not block the antibody binding to the P120 antigen. This study provides a basis for drug design for specific binding to the epitope region of the P120 protein.