Identification of Sunflower Seed IgE-Binding Proteins

BACKGROUND: Sunflower seed can cause severe anaphylactic reactions in some susceptible individuals. It is conceivable that the 2S sunflower seed protein is an allergen based on its high degree of homology (34%) with the allergenic mature 2S albumin protein of the Brazil nut. The first step in determining the allergenicity of sunflower seed proteins is to identify IgE-binding proteins. METHODS: Sera from sunflower seed-sensitive individuals were evaluated by radioallergosorbent test (RAST), isoelectric focusing (IEF) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting with sunflower seed proteins. RESULTS: Positive RAST scores (>2) were observed in 3 individuals and immunoblotting demonstrated IgE-binding to 2-7 distinct proteins ranging in size from 10 to 50 kD. Two out of 3 sera recognized two proteins between 16 and 17 kD. The lower molecular weight protein (16 kD) approximates to the prepo region of the precursor methionine-rich 2S albumin protein found in sunflower seed (SFA-8/SSA). IEF followed by immunoblotting demonstrated several IgE-binding proteins, including two proteins with isoelectric points of 5.97 and 5.3, respectively, which are consistent with the mature and immature forms of the SFA-8/SSA region. CONCLUSIONS: Sunflower seed contains several IgE-binding proteins, including regions of the high-methionine 2S albumin SFA-8/SSA.