Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2008
Publication Date: 1/12/2009
Citation: Kim, W., Jang, S., Kerley, M., Krishnan, H.B. 2009. All Three Subunits of Soybean Beta-Conglycinin are Potential Food Allergens. Journal of Agricultural and Food Chemistry. 57:938-943.
Interpretive Summary: Soybeans are extensively used as food for humans and feed for animals. Some soy proteins can cause allergic responses in humans. Soybean allergy is most common among children nourished with soybean-based infant formula. Soybean 7S storage protein, the beta-conglycinin, has been identified as one of the most allergenic proteins. The beta-conglycinin is composed of three subunits namely alpha prime (76 kDa), alpha (72 kDa) and beta (52 kDa). These subunits share extensive amino acid sequence homology. Previous studies have identified that only the alpha-subunit of beta-conglycinin, but not the other two subunits, is an allergen. We have identified several soy proteins that elicit allergic reactions in humans and demonstrate that all the three subunits of beta-conglycinin are potential allergens. Our study provides valuable information toward an understanding of the molecular basis of allergenicity. Information from our study will assist in construction of non-allergenic soybean proteins. Development of hypoallergenic soybeans will greatly enhance the nutritive value of soybean.
Technical Abstract: Soybeans are recognized as one of the “big 8” food allergens. IgE antibodies from soybean-sensitive patients recognize more than 15 soybean proteins. Among these proteins only the alpha-subunit of beta-conglycinin, but not the highly homologous alpha prime- and beta-subunits, has been shown to be a major allergenic protein. The objective of this study was to examine if the alpha prime and beta-subunits of beta-conglycinin can also serve as potential allergens. Immunoblot analysis using sera collected from soybean-allergic patients revealed the presence of IgE antibodies that recognized several soy proteins including a 72 kDa, 70 kDa, 52 kDa, 34 kDa and 21 kDa proteins. Matrix-assisted Laser Desorption Ionization Time-of-Flight mass spectrometry (MALDI-TOF) analysis of trypsin digested 72 kDa, 70 kDa and 52 kDa proteins indicated that these proteins were the alpha prime, alpha, and beta-subunits of beta-conglycinin, respectively. Additionally, purified alpha prime, alpha, and beta-subunits of beta-conglycinin were recognized by IgE antibodies present in the soybean-allergic patients. The IgE reactivity to the beta-subunit of beta-conglycinin was not abolished when this glycoprotein was either deglycosylated using glycosidases or expressed as a recombinant protein in E. coli. Our results suggest that in addition to the previously recognized alpha-subunit of beta-conglycinin, the alpha prime and beta-subunits of beta-conglycinin also are potential food allergens.