All-D peptides recognized by an anti-carbohydrate antibody identified from a positional scanning library
Article
Pinilla, C, Appel, JR, Campbell, GD et al. (1998). All-D peptides recognized by an anti-carbohydrate antibody identified from a positional scanning library
. JOURNAL OF MOLECULAR BIOLOGY, 283(5), 1013-1025. 10.1006/jmbi.1998.2137
Pinilla, C, Appel, JR, Campbell, GD et al. (1998). All-D peptides recognized by an anti-carbohydrate antibody identified from a positional scanning library
. JOURNAL OF MOLECULAR BIOLOGY, 283(5), 1013-1025. 10.1006/jmbi.1998.2137
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.
