Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2007
Publication Date: 3/26/2008
Citation: Xiang, P., Baird, L.M., Jung, R., Zeece, M.G., Markwell, J., Sarath, G. 2008. P39, a novel soybean protein allergen belongs to a plant-specific protein family, and is present in protein storage vacuoles. Journal of Agricultural and Food Chemistry Vol 56: 2266-2272. Interpretive Summary: During processing of soybean seeds, an important byproduct is soybean lecithins. Soy lecithins are seeing increasing use in industry as an emulsifier and food additive. However, lecithins also contain trace amounts of soy proteins. In this work we have thoroughly examined one soy lecithin-associated protein termed P39. Results suggest that P39 and its related homologs could be allergenic.
Technical Abstract: Soybean lecithins are seeing increasing use in industry as an emulsifier and food additive. They are also a growing source of human food allergies, which arise principally from the proteins fractionating with the lecithin fraction during manufacture. In a previous study (Gu et al., (2001) Identification of IgE-binding proteins in soy lecithin. Int. Arch. Allergy Immunol: 126, 218-225), we identified several allergenic proteins in soybean lecithins and discovered a soybean IgE-binding protein termed P39. However, very little was known about this protein except that it was coded by the soybean genome. In this paper we have investigated key biological and immunological properties of this potential soybean lecithin allergen. P39 is encoded by a multigene family in soybeans and in several other higher plants. We have cloned and studied the soybean P39-1 protein and its essentially indistinguishable homolog, P39-2. These proteins and their homologs belong to a family of plant-specific proteins of unknown function. In soybeans, P39-1 is seed specific and its transcript levels are highest in maturing seeds and decline in older seeds. In contrast, P-39 protein was detectable only in the fully mature, dry seed. Sub-cellular fractionation revealed that P-39 protein was strongly associated with oil-bodies, however, immunolocalization indicated P-39 was distributed in the matrix of the protein storage vacuoles, suggesting that association with oil bodies was an artifact arising from the extraction procedure. Using recombinant techniques we have also documented that IgE-binding epitopes are present on several different portions of the P39-1 polypeptide.