Mimotope selection of blood group A antigen from a phage display 15-mer peptide library.

We select the peptide mimics of blood group A antigen by a monoclonal anti-A from a phage display 15-mer peptide library. Monoclonal anti-A was used in biopanning a phage display 15-mer peptide library. After four rounds of panning, ELISA was carried out to confirm the positive phage clones. The exogenous DNAs of the positive phages were sequenced and the corresponding amino acid sequences were deduced. Both the synthesized peptide and the phage clones were used to bind to anti-A in competitive ELISA. Erythrocyte agglutination inhibition tests were carried out to determine the mimic ability of the free synthesized peptide to the natural blood group A antigen. Computer softwares were used to simulate the interaction between the peptide and anti-A. After four rounds of biopanning, the eluted phage reached an enrichment of approximately 1600 times. Thirty-seven phage clones were chosen randomly and amplified. There were eleven clones that interacted specifically with anti-A in ELISA. DNA sequencing of the inserted oligonucleotide revealed that nine clones present a same peptide - TRWLVYFSRPYLVAT (named TRW) and each of the other two clones presented a different peptide. The synthesized free peptide TRW could inhibit the interaction of both phage displayed peptide and group A red blood cell with anti-A in competitive ELISA and hemagglutination inhibition test. Both the peptide TRW and the natural group A antigen were docked into a same cavity of anti-A in a computer simulation assay. The results indicate that peptide TRW can mimic blood group A antigen. It may be used as a proxy of natural blood group A antigen in clinical application.