A Seed Storage Protein with Possible Self-Affinity through Lectin-Like Binding

The primary storage protein of oat (Avena sativa L.) seeds, globulin, was shown to have a specific carbohydrate-binding activity. The globulin was capable of hemagglutinating rabbit red blood cells and this hemagglutination was inhibited by the beta-glucan, laminarin, as well as by carbohydrate which had been cleaved from the native globulin. Globulin with carbohydrate-binding activity was isolated from cell wall preparations and from defatted flour. The lectin activity apparently resides in the alpha-subunit of the globulin and has affinity for the carbohydrate which is O-glycosidically linked to the globulin. A portion of this carbohydrate is attached to the beta-subunit. Two affinity columns were synthesized utilizing laminarin and the carbohydrate from the native globulin as ligands. The hemagglutinating activity bound to both of these columns. The activity was specifically eluted from the globulin-carbohydrate affinity column with carbohydrate cleaved from native globulin by an alkali-catalyzed beta-elimination. The possible roles of this unique self-binding capacity are discussed.