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The determination of epitope relating to BAC5 McAb using random peptide library (RPL)

Objective To determine the epitope relating to BAC5 McAb, a kind of monoclonal antibody located on the surface of nasopharyngeal carcinoma (NPC) cells. Methods Using BAC5 McAb as selected target 3 rounds of biopanning to a 12 mer random peptide library (RPL) displayed by M13 phages were carried out. The positive M13 phage clones were selected and identified by a sandwich ELISA. The exogenous DNA fragments in the positive/negative M13 phages were sequenced to deduce and compare the sequence of the amino acids of exogenous peptides during the phage clones. Results 77% (35/45) of the phages eluted from the 3rd round of biopanning was captured by BAC5 McAb. Three peptides were displayed by M13 phages from the 8 positive clones identified with competitive assay. The same character of “ P V ” structure existed near N terminus of the 3 different peptides, i.e. H Q S H Y P Y P V V S L (4/8), Q N Q A W F S Q P V R M (3/8) and T Q A Y K G F P V L P S (1/8) in comparison with the peptide“ N H Q S T F W Q K W T A ” displayed by M13 phages from the random selective negative clones (6/6). Conclusion BAC5 McAb recognized the three kinds of peptides with P V structure near N terminus. These peptides shared the structure with the epitope on the surface of NPC cells.