Ana o1, a cashew (Anacardium occidental) allergen of the vicilin seed storage protein family (1)
Cashew nuts have been associated with contact or systemic dermatitis (to cardol and anacardic acid found in the cashew nut shell oil1), atopic dermatitis, and IgE-mediated systemic allergic reactions.
A Ana o1.0101 (Ao1.1) represents the longest version of the cDNAs, and Ana o1.0102 (Ao1.2) is the truncated version. Note that only a single nucleotide substitution (A for G) at residue 994 distinguishes Ao1.1 and Ao1.2 in their region of common overlap, suggesting that this represents an allelic difference. Analysis of the deduced amino acid sequence revealed a 540-amino-acid open-reading frame, a possible start codon at position 3, and possible leader peptide from 3 to 28.
A search of Genbank revealed that Ao1.1 and Ao1.2 encode members of the 7S (vicilin) superfamily of proteins. Sequences with the highest amino acid identity and similarity were in the 33% to 43% and 52% to 62% range, respectively, and were variously described as vicilins and sucrose-binding proteins and their precursors and 7S globulins from nut and seed crops.
IgE from 10 of 20 sera from patients with a history of life-threatening reactions to cashews bound the recombinant.
It can be seen that recombinant protein inhibits IgE binding to a band of molecular mass of approximately 50 kd. The native precursor, corresponding to our approximately 65-kd recombinant protein, appears to undergo further cleavage as in other vicilin group proteins.
Three of the identified epitopes were bound by patient sera from all 3 pools. Only 4 of the 11 Ana o 1 and 23 Ara h 1 linear epitopes showed significant (≥7 amino acids) positional overlap.
The 7S globulins from legumes are referred to as vicilins and are seed storage proteins that often exist as large trimeric oligomers in the seed protein bodies, with individual subunits usually 40 to 70 kd in size. Peanut vicilin, Ara h 1, has been shown to resist proteolysis when in a trimeric configuration, a property that may contribute to its allergenicity. The linear epitopes, rather than the conformational epitopes, have been reported to be better predictors of allergy persistence, as in cows’ milk allergy. Cashew Ana o 1 and the major allergen in peanuts, Ara h 1, are both vicilins and both express multiple epitopes; in fact, 23 linear epitopes have been described for Ara h 1.