IgE epitope mapping of soybean glycinin G1 acidic chain

Several soy proteins have been identified as allergenic to people with a food allergy to soy-based foods. The main characteristic of allergens is the binding of immunoglobulin E (IgE) molecules from sensitized individuals. Through immunoblotting with sera pooled from soy-allergic individuals and N-terminal sequencing of IgE-binding proteins, glycinin G1 acidic chain was identified as an IgE-binding protein. Similar techniques were employed with in situ digestion with endoproteinase Glu-C of glycinin G1 acidic chain to limit the IgE-binding to a 15 kD region encompassing residues F192 to K306. Plasmid DNA constructs were designed to represent the glycinin G1 acidic chain in overlapping fragments expressed as a fusion protein with an inactive form of E. coli thioredoxin. Six purified fusion fragment proteins were used in immunoblotting experiments to show that the IgE-binding region of glycinin G1 acidic chain with the recombinant proteins was identical to the region identified with the native glycinin G1 acidic chain. The same fusion fragment proteins were used in a novel ELISA that identified the same IgE-binding region but illustrated the method\u27s ability to retain protein folding of the fusion proteins. Overlapping synthetic peptides were used in immunoblotting to identify two IgE epitopes in soybean glycinin G1 acidic chain. The identified epitopes consisted of residues G217-V235 and G253-I265. The similarity of these epitopes to IgE epitopes from other food sources and structural implications are discussed