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Three-Dimensional Structure of the Cross-Reactive Pollen Allergen Che a 3: Visualizing Cross-Reactivity on the Molecular Surfaces of Weed, Grass, and Tree Pollen Allergens¹

Petra Verdino^*, Rodrigo Barderas^2,, Mayte Villalba, Kerstin Westritschnig, Rudolf Valenta^,, Rosalia Rodriguez and Walter Keller^3,*

^* Institute of Chemistry, Structural Biology, University of Graz, Graz, Austria; Department of Biochemistry and Molecular Biology, Faculty of Chemistry, Complutense University, Madrid, Spain; and Christian Doppler Laboratory for Allergy Research and Division of Immunopathology, Department of Pathophysiology, Medical University of Vienna, Vienna, Austria

Two EF-hand calcium-binding allergens (polcalcins) occur in the pollen of a wide variety of unrelated plants as highly cross-reactive allergenic molecules. We report the expression, purification, immunological characterization, and the 1.75-Å crystal structure of recombinant Che a 3 (rChe a 3), the polcalcin from the weed Chenopodium album. The three-dimensional structure of rChe a 3 resembles an -helical fold that is essentially identical with that of the two EF-hand allergens from birch pollen, Bet v 4, and timothy grass pollen, Phl p 7. The extensive cross-reactivity between Che a 3 and Phl p 7 is demonstrated by competition experiments with IgE Abs from allergic patients as well as specific Ab probes. Amino acid residues that are conserved for the two EF-hand allergen family were identified in multiple sequence alignments of polcalcins from 15 different plants. Next, the three-dimensional structures of rChe a 3, rPhl p 7, and rBet v 4 were used to identify conserved amino acids with high surface exposition to visualize surface patches as potential targets for the polyclonal IgE Ab response of allergic patients. The essentially identical three-dimensional structures of rChe a 3, rPhl p 7, and rBet v 4 explain the extensive cross-reactivity of allergic patients IgE Abs with two EF-hand allergens from unrelated plants. In addition, analyzing the three-dimensional structures of cross-reactive Ags for conserved and surface exposed amino acids may be a first approach to mapping the conformational epitopes on disease-related Ags that are recognized by polyclonal patient Abs.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by Grants F1805 and F1815 of the Austrian Science Fund, by the Christian Doppler Research Association, and by Grants SAF02-02711 and SAF05-01847 from the Ministerio de Educación y Ciencia, Spain.

² Current address: Protein Technology Unit, Biotechnology Program, Spanish National Cancer Center, Centro Nacional de Investigaciones Oncológicas, 28029 Madrid, Spain.

³ Address correspondence and reprint requests to Dr. Walter Keller, Institute of Chemistry, Structural Biology, University of Graz, Heinrichstrasse 28, A8010 Graz, Austria. E-mail address: walter.keller{at}uni-graz.at