Inconsistencies in Determining Bacillus thuringiensis Toxin Binding Sites Relationship by Comparing Competition Assays with Ligand Blotting

Abstract

Receptor binding properties of Cry1Aa, Cry1Ab, and Cry1Ac Bacillus thuringiensis toxins to Lymantria dispar brush border membrane vesicles (BBMV) were investigated by competition assays and BBMV ligand blotting. Homologous competition binding assays demonstrated that all Cry1A toxins bound to L. dispar BBMV with high binding affinities. Heterologous competition assays suggested that all three toxins share the same binding sites. However, our ligand blotting experiments were not consistent with the heterologous competition assays. We identified a 120 kDa peptide as a Cry1Ac binding protein and a 210 kDa peptide as a Cry1Aa and Cry1Ab binding protein. These results indicated that determining the relationships between toxin binding sites by either competition assays or ligand blotting alone may not be conclusive.