Homology modeling and characterization of IgE binding epitopes of mountaincedar allergen Jun a 3

The Jun a 3 protein from mountain cedar (Juniperus ashei) pollen, a member of group 5 of the family of plant pathogenesis-related proteins (PR-protein s), reacts with serum IgE from patients with cedar hypersensitivity. We use d the crystal structures of two other proteins of this group, thaumatin and an antifungal protein from tobacco, both similar to 50% identical in seque nce to Jun a 3, as templates to build homology models for the allergen. The in-house programs EXDIS and FANTOM were used to extract distance and dihed ral angle constraints from the Protein Data Bank files and determine energy -minimized structures. The mean backbone deviations for the energy-refined model structures from either of the templates is <1 Angstrom, their conform ational energies are low, and their stereochemical properties (determined w ith PROCHECK) are acceptable, The circular dichroism spectrum of Jun a 3 is consistent with the postulated beta-sheet core. Tryptic fragments of Jun a 3 that reacted with IgE from allergic patients all mapped to one helical/l oop surface of the models. The Jun a 3 models have features common to aeros ol allergens from completely different protein families, suggesting that te rtiary structural elements may mediate the triggering of an allergic respon se.