title: All-D peptides recognized by an anti-carbohydrate antibody identified from a positional scanning library.
abstract: Monoclonal antibodies recognize antigens with high affinity and specificity, but the structural basis for molecular mimicry remains unclear. It is often assumed that cross-reactive antigens share some structural similarity that is specifically recognized by a monoclonal antibody. Recent studies using combinatorial libraries, which are composed of millions of sequences, have examined antibody cross-reactivity in a manner entirely different from traditional epitope mapping approaches. Here, peptide libraries were screened against an anti-carbohydrate monoclonal antibody for the identification of peptide mimics. Positional scanning libraries composed of all-l or all-d hexapeptides were screened for inhibition of monoclonal antibody HGAC 39.G3 binding to an antigen displaying N-acetyl-d-glucosamine (GlcNAc) residues on a polyrhamnose backbone. Inhibitory activity by mixtures from the all-d hexapeptide library was greater than the activity from the all-l libraries. The most active d-amino acid residues defined in each of the six positions of the library were selected to prepare 27 different individual hexapeptides. The sequence Ac-yryygl-NH2 was specifically recognized by mAb HGAC 39.G3 with a relative affinity of 300 nM when measured in a competitive binding assay. The contributions to overall specificity of the residues of the all-d peptide (Ac-yryygl-NH2) in binding to mAb HGAC 39.G3 were examined with a series of truncation, l and d-amino acid substitution, and retro analogs. Dimeric forms of the all-d peptide were recognized with tenfold to 100-fold greater affinities relative to the monomer. The all-d peptide was found to inhibit mAb HGAC 39.G3 binding to an anti-idiotype antibody with approximately 1000-fold greater affinity than GlcNAc. As demonstrated here, the study of immune recognition using combinatorial chemistry may offer new insights into the molecular basis of cross-reactivity.
authors.affiliation: Torrey Pines Institute for Molecular Studies, 3550 General Atomics Court, San Diego, CA, 92121, USA. pinilla@tpims.org
authors.forename: C
authors.initials: C
authors.lastname: Pinilla
authors.forename: J R
authors.initials: JR
authors.lastname: Appel
authors.forename: G D
authors.initials: GD
authors.lastname: Campbell
authors.forename: J
authors.initials: J
authors.lastname: Buencamino
authors.forename: N
authors.initials: N
authors.lastname: Benkirane
authors.forename: S
authors.initials: S
authors.lastname: Muller
authors.forename: N S
authors.initials: NS
authors.lastname: Greenspan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D000941:Antigens / Q000737:chemistry; D002241:Carbohydrates / Q000737:chemistry* / Q000276:immunology*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D018716:Molecular Mimicry; D009842:Oligopeptides / Q000737:chemistry* / Q000276:immunology*; D019151:Peptide Library; D013237:Stereoisomerism
chemical_list: D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D000941:Antigens; D002241:Carbohydrates; D009842:Oligopeptides; D019151:Peptide Library