Identification of sesame seed allergens by 2-dimensional proteomics and Edman sequencing: seed storage proteins as common food allergens

Abstract

Background: Sesame seed allergy is becoming increasingly prevalent, probably because of its use in international fast-food and bakery products. Despite this fact, few studies have focused on the identification of its major allergenic proteins.

Objective: The aim of this study was to identify allergenic proteins of sesame seeds (Sesamum indicum).

Methods: Extracted sesame seed proteins were separated by means of SDS-PAGE and 2-dimensional (2-D) PAGE. Immunolabeling was performed with individual patient sera from 20 patients with sesame seed allergy. Selected proteins were further analyzed by means of Edman sequencing.

Results: IgE-binding proteins were identified at 78, 52, 45, 34, 32, 29, 25, 20, 9, and 7 kd. Analyzing internal sequences, the protein at 45 kd, which was recognized by 75% of the patients, was found to be a 7S vicilin-type globulin, a seed storage protein of sesame and named Ses i 3. The protein at 7 kd was found to be a 2S albumin, another seed storage protein of sesame and named Ses i 2. Seed storage proteins are known food allergens in peanut, walnut, Brazil nut, and soybean. Interestingly, one known IgE-binding epitope of the peanut allergen Ara h 1 has 80% homology with the corresponding area of Ses i 3. The different amino acids were previously shown not to be critical for IgE binding in Ara h 1. In addition, the proteins at 78 and 34 kd were found to be homologous to the embryonic abundant protein and the seed maturation protein of soybeans, respectively.

Conclusion: The identification of 4 sesame seed allergens is the first step toward generating recombinant allergens for use in future immunotherapeutic approaches. In addition, the detection of conserved IgE binding epitopes in common food allergens might be a useful tool for predicting cross-reactivity to certain foods.