Background: Although mustard seed allergy has been largely reported during the preceding 20 years, currently only 2 allergens, Sin a 1 and Bra j 1, have been identified.
Objective: To improve the characterization of the allergenic profile of yellow mustard seeds by reporting the identification and biochemical characterization of an 11S globulin as a new major allergen.
Methods: Mustard seed proteins were separated using size exclusion and ion-exchange chromatographic columns, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 2-dimensional polyacrylamide gel electrophoresis. Separation of different polypeptide chains was achieved by reverse-phase high-performance liquid chromatography. Mass spectrometry after tryptic digestion and Edman degradation were used to determine amino acid sequences of peptides. IgE binding assays were performed with 13 serum samples from mustard allergic patients in immunoblotting and enzyme-linked immunosorbent inhibition assays.
Results: A protein of 51 kDa was recognized as a major allergen by patients allergic to mustard and called Sin a 2. The allergen was dissociated in 2 chains of 36 and 23 kDa, which also bound IgE. N-terminal end and internal amino acid sequences allowed identification of the new allergen as a seed storage 11S globulin belonging to the Cupin super family. Purified allergen was able to inhibit the IgE binding of sera from allergic patients to mustard seeds extract in up to 55% of the responses.
Conclusions: An 11S globulin storage protein has been isolated and identified as a novel major allergen of mustard seeds.