Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2010
Publication Date: 1/12/2011
Citation: Krishnan, H.B., Jang, S., Kim, W., Kerley, M.S., Oliver, M.J., Trick, H.N. 2011. Biofortification of soybean meal: immunological properties of the 27kDa gamma-zein. Journal of Agricultural and Food Chemistry. 59:1223-1228. Interpretive Summary: Soybeans are an excellent source of protein for livestock and soybean meal is commonly used as a feed supplement. However, they are deficient in the sulfur-containing amino acids cysteine and methionine. Consequently, animals consuming mainly a grain-based diet have to be supplemented with synthetic amino acids to maintain optimal growth and development. Numerous attempts have been made to improve the concentration of sulfur-containing amino acids in soybean. One commonly used approach involves the expression of foregin seed proteins rich in sulfur-containing amino acids in legumes. The maize 27 kD zein, which codes for a sulfur amino acid-rich protein, has been introduced into soybean in order to improve its nutritional quality. However, we still do not know if the addition of these proteins is efficacious in increasing the performance of livestock. Previously, we have demonstrated that maize 27 kD protein can elicit immunological response in young pigs when introduced into the tissues subcutaneously. In this study, we investigate the possibility that the 27 kD zein may have the potential to act as a food allergen. We demonstate that the 27kD zein does bind to human sera that cross reacts with maize proteins, both as isolated protein and in a soybean extract. Our study indicates that the 27kD protein may affect the performance of livestock if used in animal feed and has the potential to limit the use of biofortified soybean meal for human consumption. Results from this study will aid researchers in the development of non-allergenic biofortified soybeans and also maize cultivars. Development of hypoallergenic soybean and maize will greatly enhance their nutritive value and expand their use in livestock industry.
Technical Abstract: Legumes, including soybeans (Glycine max), are deficient in sulfur-containing amino acids which are required for the optimal growth of monogastric animals. This deficiency can be overcome by expressing heterologous proteins rich in sulfur-containing amino acids in soybean seeds. A maize 27 kDa gamma-zein, a cysteine-rich protein, has been successfully expressed in several crops including soybean, barley and alfalfa with the intent to biofortify these crops for animal feed. Previous work has indicated that the maize 27 kDa zein may ellicit an immune response in livestock as this abundant seed storage protein can withstand digestion by pepsin and can elicit an immunogenic response in young pigs. Using sera from patients who tested positive by ImmunoCAP assay for elevated IgE to maize proteins, we demonstrate specific IgE binding to the 27 kDa gamma-zein. Bioinformatic analysis using the full-length and 80 amino acid sliding window FASTA searches identified significant sequence homology of the 27 kDa gamma-zein with several known allergens. Immunoblot analysis using human serum that cross reacts with maize seed proteins also revealed specific IgE-binding to the 27 kDa gamma-zein in soybean seed protein extracts containg the 27kD zein. Our study demonstrates for the first time the allergenicity potential of the 27 kDa gamma-zein and the potential that this protein can limit livestock performance when used in soybeans that serve as a biofortified feed supplement.