Proteomic and immunological characterization of a new food allergen from hazelnut (Corylus avellana).

UNLABELLED: Hazelnuts (Corylus avellana) are one of the most common sources of life-long IgE-mediated food allergies. In this study, we investigated the IgE-reactivity pattern of children with hazelnut allergy (N=15) from Regione Campania, located in Southern Italy, and addressed proteomic strategies for characterizing IgE-binding proteins. For all of the patients (15/15), the predominant IgE-reactive component was a minor ~55kDa protein not previously described. Similar to the hazelnut 11S globulin Cor a 9 allergen, the immunoreactive protein consisted of two subunits linked via a disulfide bridge. In contrast to Cor a 9, only the 20.7kDa alkaline subunit exhibited IgE-affinity. The immunogenic subunit was purified by a two-step chromatographic procedure, but peptide mass fingerprinting was unsuccessful in identifying it, due to the incompleteness of the annotated hazelnut genome. Several tryptic peptides were de novo sequenced by tandem mass spectrometry and showed a high degree of homology with the 11S globulin storage proteins from other seeds, some of which have already been reported as food allergens. The structural characterization suggests that the new putative allergen is a divergent isoform of the hazelnut 11S globulin. These results provide a new platform for developing innovative diagnostic and therapeutic intervention plans.

BIOLOGICAL SIGNIFICANCE: Over the years, at least five proteins have been reported as potential food hazelnut allergens. The predominance of specific allergens appears to be strictly related to the geographical origin of the allergic subjects. The complex patterns of the IgE-reactivity of hazelnut storage proteins result in a poor diagnostic and prognostic accuracy. In the perspective of a component-resolved "molecular approach" to the hazelnut allergy we investigated the immune-reactivity patterns to hazelnuts of 15 patients (14 in the pediatric age range) from Region Campania, located in Southern Italy. For all the patients the predominant IgE-reactive component was a minor ~55kDa protein not previously annotated in either protein or genomic databases. The putative allergen was isolated, partially characterized by MS/MS de novo sequencing and appears to be an isoallergen of the hazelnut 11S globulin Cor a 9. Like this latter, the immunoreactive protein consisted of two subunits linked via a disulfide. In contrast to Cor a 9, only the 20.7kDa alkaline subunit exhibited IgE-affinity, in analogy to 11S allergens from other seeds (pistachio, cashew, soybean). We believe that the application of combined immunochemical and proteomic strategies to characterize the new food allergen could be of interest for the readers of Journal of Proteomics. In addition, the results of this study have functional worth in providing a new platform to plan innovative diagnostic and therapeutic intervention approaches to treat hazelnut allergy.