Characterization of a birch pollen allergen, Bet v III, representing a novel class of Ca super(2+) binding proteins; specific expression in mature pollen and dependence of patients' IgE binding on protein-bound Ca super(2+)

A cDNA coding for a birch pollen allergen, Bet v III, with significant sequence homology to Ca super(2+) binding proteins was isolated from an expression cDNA library using serum IgE from a patient who was allergic to pollen. The deduced amino acid sequence of the pollen allergen contained three typical Ca super(2+) binding sites. Peptides mimicking the Ca super(2+) binding sites of Bet v III were synthesized and shown to bind super(45)Ca in blot overlays. The binding of patients' IgE to the recombinant allergen depended on the native protein conformation and protein-bound Ca super(2+). Depletion of Ca super(2+) led to a reversible loss of the IgE binding thus representing a conformational IgE epitope adopted by a polypeptide upon Ca super(2+) binding. By RNA hybridization it was demonstrated that Bet v III is expressed preferentially in mature pollen. Bet v III therefore represents a pollen allergen which because of its unique structural features also belongs to a novel class of Ca super(2+) binding proteins.