Characterization of Structural Variability of the Allergenic 2S Albumin Ses i 1 Using Combinatorial Proteomics

Allergy to sesame seeds is a food allergy of high relevance due to its high abundance and the potential to elicit allergenic reactions, possibly resulting in anaphylaxis. The major sesame allergen Ses i 1 is a 2S albumin belonging to the family of seed storage proteins and despite its high allergenicity, comprehensive knowledge about Ses i 1 variants is still lacking. We, therefore, performed a detailed sequence analysis and characterized the C- and N-terminal ragged clipping of the small and large subunit of Ses i 1 using high-resolution mass spectrometry and the combination of bottom–up, middle–down, and top–down proteomic approaches. We detected extensive clipping at the C-terminus of the large (3–9 aa) and the small subunit (0–7 aa). In addition, the N-terminal conversion from glutamine to pyroglutamate and limited N-terminal clipping was confirmed for both subunits. Furthermore, we observed a sequence conflict at position 147 of Ses i 1 as well as a sequence shift of the large subunit compared to the reference sequence of the precursor.