Barley ¦Ã3-hordein: Glycosylation at an atypical site, disulfide bridge analysis, and reactivity with IgE from patients allergic to wheat
文摘
Post translational modifications of a seed storage protein, barley ¦Ã3-hordein, were determined using immunochemical and mass spectrometry methods. IgE reactivity towards this protein was measured using sera from patients diagnosed with allergies to wheat. N-glycosylation was found at an atypical Asn-Leu-Cys site. The observed glycan contains xylose. This indicates that at least some ¦Ã3-hordein molecules trafficked through the Golgi apparatus. Disulfide bridges in native ¦Ã3-hordein were almost the same as those found in wheat ¦Ã46-gliadin, except the bridge involving the cysteine included in the glycosylation site. IgE reacted more strongly towards the recombinant than the natural ¦Ã3-hordein protein. IgE binding to ¦Ã3-hordein increased when the protein sample was reduced. Glycosylation and disulfide bridges therefore decrease epitope accessibility. Thus the IgE from patients sensitized to wheat cross-react with ¦Ã3-hordein due to sequence homology with wheat allergens rather than through shared carbohydrate determinants.