Characterization of oligopeptides that cross-react with carbohydrate-specific antibodies by real time kinetics, in-solution competition enzyme-linked immunosorbent assay, and immunological analyses

Phage displaying random cyclic 7-mer, and linear 7-mer and 12-mer peptides at the N terminus of the coat protein, pIII, were panned with the murine monoclonal antibody, 9-2-L379 specific for meningoeoccal lipo-oligosaccharide. Five cyclic peptides with two sequence motifs, six linear 7-mers, and five linear 12-mers with different sequence motifs were identified. Only phage displaying cyclic peptides were specifically captured by and were antigenic for 9-2-L379. Monoclonal antibody 9-2-L379 exhibited "apparent" binding affinities to the cyclic peptides between 11 and 184 nm, comparable with lipo-oligosaccharide. All cyclic peptides competed with the binding of 9-2-L379 to lipo-oligosaccharide with EC50 values in the range 10-105 pm, which correlated with their apparent binding affinities. Structural modifications of the cyclic peptides eliminated their ability to bind and compete with monoclonal antibody 9-2-L379. Mice (C3H/HeN) immunized with the cyclic peptide with optimal apparent binding affinity and EC50 of competition elicited cross-reactive antibodies to meningococcal lipo-oligosaccharide with end point dilution serum antibody titers of 3200. Cyclic peptides were converted to T-cell-dependent immunogens without disrupting these properties by C-terminal biotinylation and complexing with NeutrAvidin(R). The data indicate that constrained peptides can cross-react with a carbohydrate-specific antibody with greater specificity than linear peptides, and critical to this specificity is their structural conformation.