Introduction Approximately 8% of children and 1–2% of adults have some type of food allergy [1], with peanuts, milk, eggs, wheat and soybeans accounting for the majority of the al- lergic reactions [2]. Food allergies, due to the ingestion of seed proteins or seed protein products, have shown an in- creasing incidence in some countries, such as the USA and Japan, where peanuts and soybeans are responsible for many atopic disorders [3]. Because of their nutritional and functional benefits, soybean proteins are now being used in- creasingly in a number of food products [4]. New process- ing methods have created a generation of soybean protein isolates with mild flavors and aromas, as well as improved functionality. These soybean proteins can be incorporated into a variety of food products at levels high enough to have an effect on the health of soybean-sensitive individuals. This has driven the food industry and soybean chemists to define the protein components responsible for soybean al- lergenicity, and to develop hypoallergenic soybean prod- ucts. Soybeans are a member of the legume family of plants that includes peanuts. Multiple protein allergens have been identified in soybean as well as in peanut extracts [5–7]. Al- Original Paper Int Arch Allergy Immunol 1998;117:29–37 Received: February 17, 1998 Accepted after revision: May 29, 1998 Cellular and Molecular Characterization of a Major Soybean Allergen Fax +41 61 306 12 34 E-Mail karger @ karger.ch www.karger.com  1998 S. Karger AG, Basel 1018–2438/98/1171–0029 $15.00/0 Accessible online at: http://BioMedNet.com/karger Correspondence to: Dr. Ricki M. Helm 1120 Marshall Street Arkansas Children’s Hospital Research Institute Little Rock, AR 72202 (USA) Tel. +1 501 320 1060, Fax +1 502 320 3173 Ricki M. Helm a Gael Cockrell a Eliot Herman c A. Wesley Burks a Hugh A. Sampson d Gary A. Bannon a,b Departments of a Pediatrics and b Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Arkansas Children’s Hospital Research Institute, Little Rock, Ark., c Climate Stress Laboratory, United States Department of Agriculture, Agricultural Research Service, Beltsville, Md., and d Division of Pediatric Allergy and Immunology, Mt. Sinai Medical School, New York, N.Y., USA Abstract Soybean proteins share a large number of cross-reacting allergens with other members of the legume family; however, soy-allergic patients rarely react clini- cally to other members of the legume family. Gly m Bd 30K, an IgE-binding pro- tein with a molecular weight of 30 kD, was identified in soybean extracts by Western IgE-immunoblot analysis. This monomeric allergen was shown to have an N-terminal amino acid sequence and amino acid composition identical to that of the seed 34-kD protein, P34, a thiol protease of the papain family. Electron- microscopic immunolocalization of P34 monoclonal antibodies and IgE binding to sections of soybean seeds showed dense staining throughout the vacuolar bod- ies, localizing the allergens in protein storage vacuoles of seed cotyledons. We used pooled serum from soybean-sensitive patients to determine the linear IgE- specific epitopes in the 34-kD allergen amino acid sequence. B-cell epitope map- ping revealed 10 regions of IgE-binding activity using an overlapping peptide strategy of 15-mers offset by 8 amino acids throughout the P34 sequence. Small- er overlapping peptides, 10-mers offset by 2 amino acids, revealed 16 distinct linear epitopes, 9 of which were mapped to the mature protein. No obvious amino acid sequence motifs could be identified by the smaller IgE-binding epi- topes. Using individual patient serum, 5 immunodominant epitopes were identi- fied in this allergen. Key Words Allergen Soybean Epitope Legumes Gly m 1 Food hypersensitivity