Molecular basis of pollen-related food allergy: Identification of a second cross-reactive IgE epitope on Pru av 1, the major cherry allergen (Prunus avium)

Division of Allergology, Paul-Ehrlich-Institut, Paul-Ehrlich-Strasse 51-59, 63225 Langen, Germany.
Biochemical Journal (Impact Factor: 4.4). 02/2005; 385(Pt 1):319-27. DOI: 10.1042/BJ20040842
Source: PubMed


Birch (Betula verrucosa) pollen-associated food allergy is a well-characterized syndrome, which is due to the cross-reactivity of IgE antibodies to homologous allergens in various foods. One crossreacting area on the major birch pollen allergen Bet v 1 and its homologue in cherry (Prunus avium) Pru av 1 has already been identified. This is the so-called 'P-loop' region, which encompasses amino acid residues around position 45 and is found on the two virtually identical tertiary protein structures. We tried to determine an additional IgE cross-reacting patch on Pru av 1 and Bet v 1. The putative IgE-binding region on Pru av 1 was localized with a mAb (monoclonal antibody) that was generated against Bet v 1, and cross-reacts with several Bet v 1 homologues in food and inhibits the binding of patients' IgE to Pru av 1. mAb reactivity pattern was analysed and amino acid positions 28 and 108 of Pru av 1 were selected and mutated by site-directed mutagenesis. The Pru av 1 mutants were produced as recombinant proteins and characterized for their folding, mAb- and IgE-binding capacity and allergenic potency with a cellular assay using the humanized rat basophilic leukaemia cell line RBL-25/30. Amino acid position 28 is involved in a second major IgE-binding region on Pru av 1 and probably on Bet v 1. The identification of this second major IgE-binding region is an essential prerequisite to understand the phenomenon of cross-reactivity and its clinical consequences, and to produce hypoallergenic proteins for an improved immunotherapy of type I allergy.

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    • "Guanidine treatment also caused a shift in the CD spectrum, consistent with a relative decrease in α-helical structure and gain of random structure. Together these findings suggest that αhelices are likely candidates for one or more conformational epitopes in Jun a 1. IgE epitopes in other allergens have been found in α-helices (Mine et al., 2003; Rafnar et al., 1998; Vrtala et al., 1999; Wiche et al., 2005). When Jun a 1 was reduced and alkylated in the presence of guanidine, there was no further decrease in IgE binding, suggesting that neither disulfide bond nor the free sulfhydryl group are required for any conformational epitopes in Jun a 1. "
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    • "Due to the polyclonal nature of the IgE response, it is difficult to analyse directly the structure of immune complexes between IgE and allergens. Therefore, most studies on IgE epitopes of Bet v 1 related allergens have focused on site-directed mutagenesis (Ferreira et al., 1998; Scheurer et al., 1999; Neudecker et al., 2003; Wiche et al., 2005; Ma et al., 2006) or, more recently on direct affinity selection and enrichment of IgE binding surface structures utilising libraries of peptide mimics (Mittag et al., 2006). In the present study we focused on the " P-loop " which has been suggested as a major epitope area on Bet v 1 (Mirza et al., 2000) and homologous food allergens (Holm et al., 2001; Neudecker et al., 2003; Mittag et al., 2006). "
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