A soybean G2 glycinin allergen - 2. Epitope mapping and three-dimensional modeling

Background: Multiple allergens have been documented in soybean extracts. Ig E from individuals allergic to soybeans, but not to peanut, has been shown by immunoblot analysis to bind to proteins with a molecular weight of appro ximately 22 kD. These findings suggested that this unique protein fraction from soybean might be responsible, in part, for soybean allergic reactivity . The objective of the present study was to characterize specific B cell ep itopes, to determine if any amino acid was critical to IgE binding and to m odel the 22-kD G2 soybean allergen to the three-dimensional (3-D) phaseolin molecule. Methods: B cell epitopes were identified using SPOTs peptide ana lysis. Structural orientation of the IgE-binding regions was mapped to the 3-D phaseolin molecule using molecular modeling of the protein tertiary str ucture. Results: Eleven linear epitopes, representing 15 amino acid peptide sequences, bound to IgE in the glycinin molecule. These epitopes were pred icted to be distributed asymmetrically on the surface of G2 trimers. Conclu sions: Only 1 epitope could be rendered non-IgE binding by alanine substitu tions in the peptide. The nonrandom distribution of the IgE binding sites p rovides new insight into their organization in trimers in 11S complexes of the G2 glycinin allergen. Copyright (C) 2000 S. Karger AG, Basel.