Characterization of peach thaumatin-like proteins and their identification as major peach allergens

Peach is the most important fruit related to food allergy in the Mediterranean area. Pru p 3, its lipid transfer protein, has been described as the principal allergen responsible for cross-reactivities with other foods and pollen and the severity of clinical symptoms. However, the involvement of other allergenic families cannot be ruled out. Thaumatin-like proteins (TLPs) have been described as food allergen in several fruits, such as apple, cherry, kiwi and banana, and pollen.

To identify members of the TLP family in peach fruit and to characterize putative allergens.

Through two-dimensional (2D) electrophoresis of peach extract and immunodetections with a pool of peach-allergic patients, IgE-binding spots were identified and the corresponding proteins purified and characterized as allergens by in vitro and in vivo assays. Three isoforms, belonging to the TLP family, were purified by different chromatographic systems and characterized by N-terminal amino acid sequences, molecular weight determination (MALDI) and enzymatic activity analysis (beta-1,3-gluconase test and inhibition growth of fungi). In the same way, their IgE-binding capacity and allergenic activity were tested by ELISA assays, basophil activation tests and skin prick tests (SPT).

Two peach-TLPs, Pru p 2.0101 and Pru p 2.0201, were identified as IgE-binding spots by 2D electrophoresis. Another peach-TLP, Pru p 2.0301, was cloned and produced as recombinant protein in a yeast system. The three isoforms were purified and characterized as TLPs by immunoblotting with anti-chestnut TLP antibodies and anti-plant N-asparagine complex glycan (anti-cross-reactive carbohydrate determinant). All of them showed beta-1,3-glucanase activity and inhibition of fungal growth. The three TLPs were recognized by around 50% of the sera from 31 patients analysed in ELISA experiments. All three gave a positive response to an SPT and/or in basophil activation experiments.

Three isoforms, belonging to the TLP family, were identified in peach as principal allergens. Their prevalence, observed in in vitro, ex vivo and in vivo analyses, suggests that they are important allergens and should therefore be included in the routine diagnosis of peach allergy, at least in the Mediterranean area.