Ana o 2, a Major Cashew (<i>Anacardium occidentale</i> L.) Nut Allergen of the Legumin Family

Abstract

Background: We recently cloned and described a vicilin and showed it to be a major cashew allergen. Additional IgE-reactive cashew peptides of the legumin group and 2S albumin families have also been reported. Here, we attempt to clone, express and characterize a second major cashew allergen. Methods: A cashew cDNA library was screened with human IgE and rabbit IgG anti-cashew extract antisera, and a reactive nonvicilin clone was sequenced and expressed as a fusion protein in Escherichia coli. Immunoblotting was used to screen for reactivity with patients’ sera, and inhibition of immunoblotting was used to identify the corresponding native peptides in cashew nut extract. The identified allergen was subjected to linear epitope mapping using SPOTs solid-phase synthetic peptide technology. Results: Sequence analysis showed the selected clone, designated Ana o 2, to encode for a member of the legumin family (an 11S globulin) of seed storage proteins. By IgE immunoblotting, 13 of 21 sera (62%) from cashew-allergic patients were reactive. Immunoblot inhibition data showed that the native Ana o 2 constitutes a major band at approximately 33 kD and a minor band at approximately 53 kD. Probing of overlapping synthetic peptides with pooled human cashew-allergic sera identified 22 reactive peptides, 7 of which gave strong signals. Several Ana o 2 epitopes were shown to overlap those of the peanut legumin group allergen, Ara h 3, in position but with little sequence similarity. Greater positional overlap and identity was observed between Ana o 2 and soybean glycinin epitopes. Conclusions: We conclude that this legumin-like protein is a major allergen in cashew nut.

Systematic review on cashew nut allergy

“…Ana o 1 is a 50 kDa vicilin-like protein resistant to heat and proteolysis. The other two known allergens are Ana o 2, a 33 kDa legume-like protein, and Ana o 3, a 13 kDa 2S albumin (14)(15)(16). All three allergens are classified as seed storage proteins.…”

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“…Ana o 1, Ana o 2, and Ana o 3 have been recognised by the serum of 50 % (Wang et al, 2002), 62 % (Wang et al, 2003), and 81 % (Robotham et al, 2005) of patients with an allergy to cashew nut, respectively. The molecular structure of Ana o 2 closely resembles that of soybean Gy2 glycinin (Robotham et al, 2010).…”

“…Allergens from cashew (Anacardium occidentale) are listed in Table 13 and include three major allergens classified as seed storage proteins: Ana o 1, a 7S vicilin-like protein with homotrimer subunits (Wang et al, 2002); Ana o 2, an 11S globulin member of the legumin family (Wang et al, 2003); and Ana o 3, a 2S albumin (Robotham et al, 2005). Ana o 1, Ana o 2, and Ana o 3 have been recognised by the serum of 50 % (Wang et al, 2002), 62 % (Wang et al, 2003), and 81 % (Robotham et al, 2005) of patients with an allergy to cashew nut, respectively.…”

Advances in allergen-microarray technology for diagnosis and monitoring of allergy: The MeDALL allergen-chip

“…Recombinant allergens were generated as previously described for Ana o 1 [19], Ana o 2 [20], Ana o 3 [21], Pru du 4 [22], Pru du 6 [23] and Pis v 3 [24].…”