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All Three Subunits of Soybean β-Conglycinin Are Potential Food Allergens

U.S. Department of Agriculture, Division of Plant Sciences, Plant Genetics Research Unit, Agricultural Research Service, University of Missouri, Columbia, Missouri 65211, USA.
Journal of Agricultural and Food Chemistry (Impact Factor: 3.11). 02/2009; 57(3):938-43. DOI: 10.1021/jf802451g
Source: PubMed

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'- and beta-subunits, has been shown to be a major allergenic protein. The objective of this study was to examine if the alpha'- 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 72, 70, 52, 34, and 21 kDa proteins. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) analysis of trypsin-digested 72, 70, and 52 kDa proteins indicated that these proteins were the alpha'-, alpha-, and beta-subunits of beta-conglycinin, respectively. Additionally, purified alpha'-, 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 Escherichia coli . The results suggest that in addition to the previously recognized alpha-subunit of beta-conglycinin, the alpha'- and beta-subunits of beta-conglycinin also are potential food allergens.

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    • "One hurdle related to the use of proteins as food ingredients is that most are allergens, such as -lactoglobulin (Selo et al., 1999), a bovine whey protein, and -conglycinin (Krishnan et al., 2009), a soy protein. However, studies have shown that the conjugation of proteins with polysaccharides decreased the level or degree of allergenicity of the protein, as reported by Li et al. (2011). "
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    • "Finally, because nePTMs occurring during technological processes may affect the allergenic properties of a protein, as previously reported, monitoring and characterization of these reactions are needed in order to assess the allergenic properties of processed foodstuffs. As an example, in contrast to other reports, a recent study [77] showed that deglycosylation did not affect the affinity of β-conglycinin (i.e. the major allergens from soybean) to IgE of patients allergic to soybean, suggesting that the glycosylation should not be involved in allergy. Analogously, many researchers aimed to understand the role and the contribution of glycosylation to allergenicity of egg proteins have provided contradictory results. "
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    • "7S β-conglycinin is composed of α, α' and β subunits, with a molecular weight of 76, 72 and 52 kDa, respectively (Thanh and Shibasaki 1977). β subunit, which has been proved to be one of the allergen source (Adachi et al. 2009; Krishnan et al. 2009), is the only subunit of major soybean seed storage protein that does not contain any cystine, cysteine or methionine. On the other hand, β subunit could enhance thermal stability and emulsifying property during the step of soy food processing (Utsumi et al. 1997; Mo et al. 2011). "
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