Molecular modeling and conformational IgG epitope mapping on bovine β-casein

Characterizing conformational B-cell epitopes is a key step for understanding the immunological basis of allergy contributed by β-casein. There is no resolved conformational structure of β-casein in protein data bank, and most of the previous research on epitope identification of β-casein focused on linear epitopes. Hence, the aim of this study is to map conformational epitopes on β-casein using molecular modeling and phage display. Phage peptides bound by the rabbit polyclonal antibodies were selected. Ten mimotopes were obtained after three rounds of bio-panning. Analysis on the structural and geometrical properties of the antibody–antigen complexes that were compiled from immune epitope database exhibited that the number of the amino acids comprised in epitope ranged from 11 to 25 with a median number of 17. Epitopes spanned an area range from 541.4 to 1131.9 Ǻ² with a median value of 782.9 Ǻ². Epitopes were enriched with asparagine, tryptophan, tyrosine, glycine and lysine, whereas alanine, cysteine, aspartate, asparagine and serine were prone to separate the epitopes into fragments. These characteristics of epitope were used to select epitope candidates based on mimotopes and conformational structure of β-casein that was built by homology modeling. Consequently, four B-cell IgG epitopes were mapped on β-casein.