On the basis of the IgE reactivity being confined to the alpha subunit and to an 18 kDa peptide starting YVVN, the IgE epitopes may be in the region 232-383 of the mature alpha chain and must differ from the non-allergenic alpha' subunit (Ogawa et al. 1995 [653]).
Allergen stability: Process, chemical, enzymatic
The storage proteins are thermostable. Temperatures in excess of 75°C are required for denaturation of beta-conglycinin and it shows only partial loss of secondary and tertiary structure (Mills et al. 2001 [114]). The proteins' ability to aggregate and gel on heating has been widely exploited in food processing but its implications for allergenicity have not been studied. They also show resistance to proteolysis, being able to form large (>100,000 dalton) oligomeric partially cleaved intermediates.
Nature of main cross-reacting proteins:
Not known. IgE cross-reactivity occurs between legumes, such as peanut and soybean, but it is generally not clinically significant. The 7S globulins Ara h 1 and beta-conglycinin are about 43% identical and may contribute to peanut -soya IgE cross-reactivity although the 11S family is slightly more conserved and may be more important. Beta-conglycinin and Len c 1 are more similar at 55% identity.
Allergen properties & biological function:
The 7S globulin (beta-conglycinin) proteins are heterotrimeric, of Mr ~ 180,000, made up of N-glycosylated subunits. In soya these are the 50 kDa beta subunit and the 63 kDa alpha/alpha' subunits (after removal of propeptides). The IgE-reactivity appears to be confined to the alpha subunit N-terminal insert.
Allergen purification:
Defatted soy flour was extracted with water (1:5, w/v) by stirring for 1h at 20C. After centrifugation (10,000xg, 20 min, 20°C) and the supernatant retained. After incubation at 2°C overnight, the cold-insoluble fraction (CIF) was removed by centrifugation at 10,000xg for 30 min, 20°C. The pH of the supernatant was adjusted to pH 5.4 with 0.1M HCl and following centrifugation at 10,000xg for 20 min at 20°C, the 7S globulin precipitated by adjusting the pH to 4.8 with 1M HCl. Following dialysis against 50mM Tris-HCl, pH 7.8, containing 0.2M NaCl the crude 7S globulin was further purified by gel filtration on Sephacryl S300 (2.6x100cm column) using a flow rate of 0.4 ml/min, to remove aggregates (after Than and Shibasaki, 1976).
Other biochemical information:
A complex of the alpha' and alpha subunits of beta-conglycinin and the allergen Gly m Bd 30K was identified by Samoto et al. (1996) [1084]. A genetically mutated soybean cultivar lacking the alpha' and alpha subunits allowed easier removal of Gly m Bd 30K from defatted soy milk (Samoto et al. 1996) [1085].
Maruyama N, Adachi M, Takahashi K, Yagasaki K, Kohno M, Takenaka Y, Okuda E, Nakagawa S, Mikami B, Utsumi S.
Crystal structures of recombinant and native soybean beta-conglycinin beta homotrimers.
Eur J Biochem. 268(12):3595-604. 2001
PUBMED ID:
11422391
Ogawa T, Bando N, Tsuji H, Nishikawa K, Kitamura K.
Alpha-subunit of beta-conglycinin, an allergenic protein recognized by IgE antibodies of soybean-sensitive patients with atopic dermatitis.
Biosci Biotechnol Biochem. 59(5):831-833. 1995
PUBMED ID:
7787297
Samoto M, Miyazaki C, Akasaka T, Mori H, Kawamura Y.
Specific binding of allergenic soybean protein Gly m Bd 30K with alpha'- and alpha-subunits of conglycinin in soy milk.
Biosci Biotechnol Biochem. 60(6):1006-1010. 1996
PUBMED ID:
8695899
Samoto M, Takahashi K, Fukuda Y, Nakamura S, Kawamura Y.
Substantially complete removal of the 34kDa allergenic soybean protein, Gly m Bd 30 K, from soy milk of a mutant lacking the alpha- and alpha'-subunits of conglycinin.
Biosci Biotechnol Biochem. 60(11): 1911-1913. 1996
PUBMED ID:
8987873
Than VH, Shibasaki K
Major proteins of soybean seeds. A straightforward fractionation and their characterization.
J Agric Food Chem 24:1111-1117. 1976
PUBMED ID:
1033950
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