An experimental and modeling-based approach to locate IgE epitopes of plant profilin allergens

Background: Plant profilins are actin-binding proteins that form a well-known panallergen family responsible for cross-sensitization between plant foods and pollens. Melon profilin, Cue m 2, is the major allergen of this fruit. Objective: We sought to map IgE epitopes on the 3-dimensional structure of Cue m 2. Methods: IgE binding to synthetic peptides spanning the full Cue m 2 amino acid sequence was assayed by using a serum pool and individual sera from 10 patients with melon allergy with significant specific IgE levels to this allergen. Three-dimensional modeling and potential epitope location were based on analysis of both solvent exposure and electrostatic properties of the Cue m 2 surface. Results: Residues included in synthetic peptides that exerted the strongest IgE-binding capacity defined 2 major epitopes (El, consisting of residues 66-75 and 81-93, and E2, consisting of residues 95-99 and 122-131) that partially overlapped with the actin-binding site of Cue m 2. Two additional epitopes (E3, including residues 2-10, and E4, including residues 35-45) that should show weaker putative antigen-antibody associations and shared most residues with synthetic peptides with low lgE-binding capacity were predicted on theoretical grounds. Conclusions: Strong and weak IgE epitopes have been uncovered in melon profilin, Cue m 2. Clinical implications: The different types of IgE epitopes located in the 3-dimensional structure of melon profilin can constitute the molecular basis to explain the sensitization and cross-reactivity exhibited by this panallergen family.