A Soybean G2 Glycinin Allergen (1)
The frequency of soybean aeroallergens was determined, at least 90% of the patients produced IgE that was specific to seed coat components with molecular weights of 7–8 kD. IgE of patients with soybean-induced asthma involved in the Barcelona asthma epidemic reacted weakly to two proteins with molecular weights of 42 and 21 kD. Isoallergens identified as Gly m 1A (molecular weight 7.5 kD) and Gly m 1B (molecular weight 7 kD) recognized IgE from 95% of the patients with soybean-induced asthma. The 2S fraction contained a very allergenic protein with a molecular weight of about 21 kD that was identified as Kunitz soybean trypsin inhibitor. Other ingested allergens include glycinin (11S proteins), ß-conglycinin (7S proteins) and the pro- tein Gly m Bd 30 kD.
To enrich the 20- to 22-kD proteins, crude soybean extracts were separated by preparative SDS-PAGE. Immunoblot analysis with pooled serum from soy-sensi- tive individuals revealed that IgE bound with high in- tensity to a protein band at approximately 20–22 kD.
Analysis by staining of blots with Coomassie blue and by autoradiographic analysis resulted in the detection of 22-kD protein spots. The other proteins present at about 45 kD are aggregated forms of the 22-kD proteins. Each basic chain from glycinin reacts with the IgEs to a similar extent.
The most prevalent primary sequence matched the basic glycinin polypeptide of G2 proglycinin as reported in the GenBank database.
The 11S glycinin fraction accounts for the largest pro- portion (150%) of the storage proteins found in most soy- bean varieties.