Hazelnut (Corylus avellana) vicilin Cor a 11:: molecular characterization of a glycoprotein and its allergenic activity

In Europe, hazelnuts (Corylus avellana) are a frequent cause of food allergies. Several important hazelnut allergens have been previously identified and characterized. Specific N-glycans are known to induce strong IgE responses of uncertain clinical relevance, but so far the allergenic potential of glycoproteins from hazelnut has not been investigated. The aim of the study was the molecular characterization of the glycosylated vicilin Cor a I I from hazelnut and the analysis of its allergenic activity. Although MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS showed that one of two potential glycosylation sites of Cor a I I was glycosylated, CD spectroscopy indicated that recombinant and natural Cor a I I share similar secondary structures. Thus to analyse the impact of the glycan residues of Cor a I I on I-E binding, the allergenic activity of natural glycosylated Cor a I I and recombinant Cor a I I was compared. In addition, the IgE sensitization pattern to recombinant Cor a 11, Cor a 1, Cor a 2 and Cor a 8 of 65 hazelnut allergic patients was determined in vitro. The prevalence of I-E reactivity to hazelnut vicilin Cor a 11 was below 50%. Basophil histamine-release assays were used to determine the allergenic activity of both natural and recombinant Cor a I I in comparison with Cor a 1, a birch (Betula verrucosa) pollen-related major hazelnut allergen. Both forms of Cor a I I induced mediator release from basophils to a similar extent, indicating that the hazelnut allergic patients had cross-linking IgE antibodies binding to the protein backbone and not to carbohydrate structures. In comparison to Cor a 1, a 10 000-fold higher concentration of Cor a 11 was required to induce similar basophil mediator release. In conclusion, the hazelnut vicilin Cor a I I is a minor allergen both in regard to prevalence and allergenic potency, whereas its glycan does not contribute to its allergenic activity.