Characterization of the epitopes recognized by monoclonal antibody 3A8 specific to broad-spectrum Gram-negative bacteria

Objective:To screen and characterize the common epitopes recognized by monoclonal antibody 3A8,which binds several kinds of Gram negative bacteria,which were recognized by monoclonol antibody 3A8 agaisnt different strains of LPS.Methods:Phage clones binding to 3A8 were screened from C7C phage displayed peptide library,the attached phage clones were eluted by LPS2630(O111:B4).After 3 rounds of panning,the positive phage clones were identified by ELISA,and the amino acid sequences of these positive clones were deduced from DNA sequences.In order to predict how these peptide mimics interaction with 3A8,peptides(A2 and A5) based on conserved sequences of positive clones were synthesized and conjugated with KLH for further study.The binding of A2-KLH and A5-KLH to 3A8 were identified by ELISA.Results:15 of 33 phage clones were identified as positive clones and shown specific binding with 3A8.LPS2630 potently inhibited the binding of phage clone to 3A8.In analysis of the amino acid sequence,there were seven kinds of sequences containing highly hydrophilic residues,and Ser Pro Pro/Pro X Pro was the conserved sequence.The peptides A2 and A5 could bind to 3A8 specially.Conclusion:The conserved sequences containing Ser Pro Pro/Pro X Pro are obtained,which are recognized by mAb 3A8 against broad spectrum Gram negative bacteria and several strain LPS.The synthetic peptides based on the conserved sequence can bind to 3A8,indicating that the peptides can mimic a common epitope of Gram negative bacteria,which be expected as candidate epitope for vaccinization.