21 Molecular Properties and Immunological Reactivity of Arabidopsis EXPB1, a Nonallergenic Homologue of Grass Group 1 Allergens

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BACKGROUND: Grass group 1 allergens are glyco-proteins of about 30kDa that are highly soluble and profusely released by grass pollen upon hydration. They bind to IgE antibodies that initiate the allergic response causing hay fever, seasonal asthma, and related immune responses in humans. Bermuda grass (Cynodon dactylon; subfamily Chloridoideae) is an important source of seasonal aeroallergens in warm tropical and sub-tropical areas worldwide. Improved approaches to diagnosis and therapy of allergic diseases require a thorough understanding of the structure and epitopes on the allergen molecule that are crucial for the antigen-antibody interaction. In order to understand structural basis of IgE reactivity of group 1 allergen Cyn d1, we have pursued a comparative genomic approach to search for hypoallergenic or non-allergenic homologues. METHODS: Gene cloning, Protein expression in bacteria, protein structure modeling, IgE reactivity analysis through Immunoblotting. RESULTS: EXPB1, an Arabidopsis protein (belonging to the beta expansin multi gene family), showed significant sequence and structural similarity to Cyn d 1. This protein was expressed in E. coli and the recombinant protein did not react with serum IgE from grass pollen allergic patients, suggesting that EXPB1 represented a non-allergenic homologue of grass group 1 allergens. It is proposed that differences in the amino acid sequence are responsible for the difference in the allergenicity profile of the Arabidopsis and grass pollen proteins. CONCLUSIONS: Our study provides valuable data for further investigations of the molecular basis of allergenicity and cross-reactivity of grass group 1 allergens.

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