A soybean G2 glycinin allergen. 2. Epitope mapping and three-dimensional modeling.
BACKGROUND
Multiple allergens have been documented in soybean extracts. IgE from individuals allergic to soybeans, but not to peanut, has been shown by immunoblot analysis to bind to proteins with a molecular weight of approximately 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 epitopes, to determine if any amino acid was critical to IgE binding and to model the 22-kD G2 soybean allergen to the three-dimensional (3-D) phaseolin molecule.


METHODS
B cell epitopes were identified using SPOTs peptide analysis. Structural orientation of the IgE-binding regions was mapped to the 3-D phaseolin molecule using molecular modeling of the protein tertiary structure.


RESULTS
Eleven linear epitopes, representing 15 amino acid peptide sequences, bound to IgE in the glycinin molecule. These epitopes were predicted to be distributed asymmetrically on the surface of G2 trimers.


CONCLUSIONS
Only 1 epitope could be rendered non-IgE binding by alanine substitutions in the peptide. The nonrandom distribution of the IgE binding sites provides new insight into their organization in trimers in 11S complexes of the G2 glycinin allergen.
Helm
R M
RM
Department of Pediatrics, University of Arkansas for Medical Sciences, Arkansas Children's Nutrition Center, Little Rock, AR 72202-3591, USA.
Cockrell
G
G
Connaughton
C
C
Sampson
H A
HA
Bannon
G A
GA
Beilinson
V
V
Nielsen
N C
NC
Burks
A W
AW
D000409:Alanine / Q000235:genetics; D000485:Allergens / Q000737:chemistry / Q000276:immunology*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D018604:Epitope Mapping; D018985:Epitopes, B-Lymphocyte / Q000276:immunology; D005512:Food Hypersensitivity / Q000097:blood / Q000276:immunology*; D005916:Globulins / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D016056:Immunodominant Epitopes / Q000032:analysis; D007073:Immunoglobulin E / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D020836:Protein Structure, Quaternary; D016415:Sequence Alignment; D030262:Soybean Proteins / Q000737:chemistry / Q000276:immunology*
D000485:Allergens; D018985:Epitopes, B-Lymphocyte; D005916:Globulins; D016056:Immunodominant Epitopes; D030262:Soybean Proteins; D007073:Immunoglobulin E; C011474:glycinin; D000409:Alanine