Ara h 2: crystal structure and IgE binding distinguish two subpopulations of peanut allergic patients by epitope diversity.
BACKGROUND
Peanut allergy affects 1% of the population and causes the most fatal food-related anaphylactic reactions. The protein Ara h 2 is the most potent peanut allergen recognized by 80-90% of peanut allergic patients.


METHODS
The crystal structure of the major peanut allergen Ara h 2 was determined for the first time at 2.7 Å resolution using a customized maltose-binding protein (MBP)-fusion system. IgE antibody binding to the MBP fusion construct vs the natural allergen was compared by ELISA using sera from peanut allergic patients.


RESULTS
The structure of Ara h 2 is a five-helix bundle held together by four disulfide bonds and related to the prolamin protein superfamily. The fold is most similar to other amylase and trypsin inhibitors. The MBP--Ara h 2 fusion construct was positively recognized by IgE from 76% of allergic patients (25/33). Two populations of patients could be identified. Subpopulation 1 (n = 14) showed an excellent correlation of IgE antibody binding to natural vs recombinant Ara h 2. Subpopulation 2 (n = 15) showed significantly reduced IgE binding to the MBP fusion protein. Interestingly, about 20% of the IgE binding in subpopulation 2 could be recovered by increasing the distance between MBP and Ara h 2 in a second construct.


CONCLUSIONS
The reduced IgE binding to the MBP--Ara h 2 of subpopulation 2 indicates that the MBP molecule protects an immunodominant epitope region near the first helix of Ara h 2. Residues involved in the epitope(s) are suggested by the crystal structure. The MBP--Ara h 2 fusion constructs will be useful to further elucidate the relevance of certain epitopes to peanut allergy.
Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA. mueller3@niehs.nih.gov
G A
GA
Mueller
R A
RA
Gosavi
A
A
Pomés
S
S
Wünschmann
A F
AF
Moon
R E
RE
London
L C
LC
Pedersen
D055516:2S Albumins, Plant / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D052179:Antigens, Plant / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D010367:Arachis / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D016056:Immunodominant Epitopes / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D007073:Immunoglobulin E / Q000276:immunology / Q000378:metabolism*; D058619:Maltose-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D021183:Peanut Hypersensitivity / Q000145:classification* / Q000175:diagnosis / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D055516:2S Albumins, Plant; D052179:Antigens, Plant; C500890:Ara h 2 allergen, Arachis hypogaea; D006023:Glycoproteins; D016056:Immunodominant Epitopes; D058619:Maltose-Binding Proteins; D011993:Recombinant Fusion Proteins; D007073:Immunoglobulin E
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