Continuous and discontinuous protein antigenic determinants

Abstract

Protein antigenic determinants have been classified as continuous or discontinuous. The continuous determinants are composed of residues which are local in the polypeptide sequence, while discontinuous determinants consist of residues from different parts of the sequence, brought together by the folding of the protein to its native structure. Searches made for protein determinants using peptide fragments which compete with protein-antibody complex formation, or peptides that can be used to raise antibodies which crossreact with the native protein, are limited to the simulation of continuous determinants. However, recent experiments suggest that most determinants are discontinuous. We now show, by consideration of protein surfaces, that if the recognition zone between a protein and antibody has the same dimensions as those found for the lysozyme-antibody complex, none of the protein's surface will be 'continuous'. We suggest that all determinants are discontinuous to some extent, and that crossreacting peptides mimic only the 'primary' interaction site. In addition, we show that the parts of a protein's surface which are most continuous fall predominantly in the loops and/or protruding regions. This explains why quantities such as hydrophilicity, accessibility, mobility and protrusion can be used to predict which parts of a polypeptide provide the 'best' antigenic peptides.

1H‐NMR conformational analysis of a high‐affinity antigenic 11‐residue peptide from the tryptophan synthase β2 subunit

“…All these results would be in favour of an exposed, rigid, continuous epitope, devoid of regular secondary structure. This does not agree with observations showing that antibodies often tend to recognize short peptides or discontinuous epitopes when the peptides correspond to mobile segments of a native protein [18,24,32-341, but does agree with those studies showing that large surface exposures [35 -371 and protruding loops [38] are the best antigenic regions.…”

Mapping of topoisomerase II α epitopes recognized by autoantibodies in idiopathic pulmonary fibrosis

“…According to their pattern of reactivity the anti-topo II a-positive sera were scored for epitope complexity as follows: 1 for contiguous, 2 for discontiguous and 3 for highly conformational epitopes in agreement with previous studies [18][19][20]32,33]. The analysis of correlation between the score of epitope complexity and the clinical data was undertaken both by means of Kendall's coefficient of correlation and by Kruskal-Wallis one-way ANOVA test to assay the variance of the three groups for each of the clinical parameters.…”

“…Moreover, analysis of the protein surfaces suggests that all determinants are discontiguous to some extent, and that cross-reacting peptides mimic only the primary interaction site [32].…”

Generation of monospecific antibodies based on affinity capture of polyclonal antibodies

“…Several reports 18,19 have suggested that the majority of antibodies recognize conformational epitopes consisting of amino acids that are brought together in space by the folding of several chains of the protein target. In contrast, the method described here relies on antibodies binding to linear epitopes, while the conformational epitopes are only recovered on the last antigen matrix.…”