Tandem repeat inserts in 13S globulin subunits, the major allergenic storage protein of common buckwheat (Fagopyrum esculentum Moench) seeds

The prevalent allergen of common buckwheat (Fagopyrum esculentum Moench) is β polypeptide of the most abundant storage protein, 13S globulin. Because the 13S globulin is composed of multiple diversified subunits, α polypeptide, the counterpart of β polypeptide in 13S globulin subunits, was characterised in depth to better understand this allergenic protein. Most α polypeptides were reactive to antibodies for 13S globulin-related rice glutelin and soybean glycinin and seemed to be methionine-poor subunits. Four new methionine-poor subunits with 0, 2, 4, and 6 tandem repeats were identified. The α polypeptides showed a comparatively significant variation in size, which was largely attributed to the different lengths of the tandem repeat inserts in methionine-poor subunits. Because the tandem repeat region was hydrophilic with many arginyl residues, digestibilities against trypsin, that is one of the critical characteristics for allergens, were different between the subunits with and without the tandem repeat.