Thermostability and in vitro digestibility of a purified major allergen 2S albumin (Ses i 1) from white sesame seeds (Sesamum indicum L.).
A major 2S albumin allergen, Ses i 1, from white sesame seeds was purified to homogeneity, characterized and identified using proteomic techniques. Ses i 1 exhibited a molecular weight of 12062 Da, although an extensive C-terminal clipping of the small subunit was observed. In addition, the N-terminal glutamine of the small subunit had been converted to pyroglutamate and a variant of the large subunit which had lost the N-terminal glutamine was also detected. The protein was thermo-stable up to 90 degrees C at neutral and acid pH, retaining its monomeric state and showing minimal alterations, which were reversible on cooling, in a predominantly alpha-helical secondary structure, as shown by circular dichroism and Fourier transform-infrared spectroscopy. Ses i 1 was also highly resistant to digestion using a physiologically relevant in vitro gastrointestinal model system. After 2 h of gastric digestion, the allergen remained completely intact and only the small subunit was cleaved during 2 h of subsequent duodenal digestion, leaving a major IgE epitope region of this protein intact. Neither prior heating of the Ses i 1 nor the presence of the physiological surfactant phosphatidylcholine affected the pattern of proteolysis. These findings are consistent with those found for the 2S albumin allergen from Brazil nut, Ber e 1, and suggest that Ses i 1 may preserve its structure from the degradation in the gastrointestinal tract, a property thought to be crucial for both a protein to sensitise the mucosal immune system and provoke an allergic reaction in a sensitised individual.
Moreno
F Javier
FJ
Institute of Food Research, Norwich Research Park, Colney Lane, Norwich NR4 7UA, United Kingdom. j.moreno@ifi.csic.es
Maldonado
Bárbara M
BM
Wellner
Nikolaus
N
Mills
E N Clare
EN
D055516:2S Albumins, Plant; D052179:Antigens, Plant / Q000737:chemistry / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004063:Digestion / Q000502:physiology; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D040901:Proteomics; D012639:Seeds / Q000737:chemistry*; D031685:Sesamum / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
D055516:2S Albumins, Plant; D052179:Antigens, Plant; D010940:Plant Proteins; C540354:Ses i 1 allergen, Sesamum indicum