Identification and Mutational Analysis of the Immunodominant IgE Binding Epitopes of the Major Peanut Allergen Ara h 2 (1)
Two highly abundant glycoproteins found in the cotyledon are the peanut allergens, Ara h 1 and Ara h2. These proteins are recognized by serum IgE from >90% of peanuts-sensitive patients. The majority of serum IgE recognition of the Ara h1 and Ara h2 allergens appear to be due to epitopes within these proteins that are linear amino acid sequences that do not contain significant amounts of carbohydrate.
The calculated size of the protein encoded by this open reading frame was 17.5 kDa, which is in good agreement with the molecular weight of Ara h 2 that has been determined experimentally.
There are three IgE binding regions along the entire length of the Ara h 2 protein that are recognized by this population of patients with peanut hypersensitivity. These IgE-binding regions represent amino acid residues 17–39, 41–80, and 114–157.
The 10 IgE-binding epitopes were identified. The size of the epitopes ranged from 6 to 10 amino acids in length. Three epitopes (aa15-24, aa21-30, and aa27-36), which partially overlapped with each other, were found in the region of amino acid residues 17–39. Four epitopes (aa39-48, aa49-58, aa57-66, and aa65-74) were found in region 41–80. Finally, three epitopes (aa115-124, aa127-136, and aa143-152) were found in the region represented by amino acid residues 114–157. No obvious amino acid sequence motif was shared with the exception of epitope 6 and 7, which contain the sequence DPYSP.
The intensity of IgE binding to each spot was determined as a function of that patient’s total IgE binding to these 10 peptides. All of the patient sera recognized epitope 3, 6, and 7.
Recent evidence suggests that there is a preferential variable heavy chain usage in IgE synthesis and a direct switching from IgM production to IgE synthesis.