Characterization of Monoclonal Antibodies that Recognize the Soybean (Kunitz) Trypsin Inhibitor: Binding to the Inhibitor Interrupts the Formation of the Trypsin : Inhibitor Complex

Abstract

Summary Three monoclonal antibodies (mAbs) have been raised against the soybean (Kunitz) trypsin inhibitor (SBTI), and designated 5H-10, 6D-12, and 7B-11 . Isotyping revealed that all three are IgG variants. Western blotting analysis has shown that (i) each monoclonal antibody specifically recognizes SBTI, but not the Bowman-Birk inhibitor (BBI) from soybean, and (ii) mAbs 5H-10 and 6D-12 recognize a peptide of the correct molecular weight in seeds of two soybean cultivars that contain distinct allelic forms of the inhibitor (designated as Ti a and Ti b ). However, binding studies using ELISA have shown that the affinity for purified SBTI differs between the clones. Further, mAb 6D-12 can interrupt the inhibition of trypsin by SBTI such that the activity of the proteinase is restored, while the other two monoclonals have no apparent effect. These results suggest that the epitope for mAb 6D-12 differs from mAbs 5H-10 and 7B-11, and as such this set o f monoclonal antibodies can be of use in further characterising the trypsin : SBTI interaction.