Gliadin is the principal allergen of wheat-dependent exercise-induced anaphylaxis (WDEIA). The primary structure of IgE-binding epitopes in wheat gliadin includes tandem sequencing sites of glutamine residues. Therefore, deamidation would be an effective approach to reduce the allergenicity of wheat proteins. In our previous study, we deamidated wheat gliadin without causing peptide-bond hydrolysis or polymerization by use of carboxylated cation-exchange resins, and we found that the deamidated gliadin scarcely reacted with the sera of patients radioallergosorbent test (RAST)-positive to wheat. In this study, we examined the allergenicity of deamidated gliadin in a mouse model of wheat-gliadin allergy. Oral administration of deamidated gliadin to gliadin-sensitized mice suppressed enhancement in intestinal permeability, serum allergen level, serum allergen-specific IgE level, mast-cell-surface expression of FcεRI, and serum and intestinal histamine levels. Our results indicate that gliadin deamidated with no peptide-bond hydrolysis by cation-exchange resins has low allergenicity even under in vivo conditions.

The interaction between soybean 7S globulin and the carboxyl groups of cation-exchange resins of the carboxylate type was analyzed by using a surface plasmon resonance (SPR) technology with relevance to deamidation of the globulin. This interaction and the degree of deamidation were measured under conditions of buffered solutions of different salt, sodium ion concentration, and pH. Soybean 7S globulin was dissolved in various solutions and mixed with cation-exchange resins of the carboxylate type. After removal of the resins, the degree of deamidation of the soybean 7S globulin was measured. The affinity of soybean 7S globulin dissolved in various solutions for the carboxyl group was analyzed with a SPR biosensor (Biacore) by using a chip with carboxylates on a dextran matrix. The deamidation level of soybean 7S globulin and the affinity of soybean 7S globulin for the polymer-supported carboxylates were well correlated. Both of them became higher at lower sodium concentrations and were highest at pH 6.0. Among the buffers examined, the phosphate buffer was the most effective for deamidation of soybean 7S globulin; and the affinity of soybean 7S globulin in this buffer for the carboxylate groups on the SPR chips was the highest in the phosphate buffer. Therefore, deamidation of 7S globulin protein would effectively occur when the amide groups of glutamine and asparagine residues of the protein interact with the carboxylates on resins.