A 106 kDa form of aminopeptidase is a receptor for Bacillus thuringiensis CryIC δ-endotoxin in the brush border membrane of Manduca sexta

A soluble 106 kDa protein with aminopeptidase activity was isolated from Manduca sexta using CryIC toxin-affinity and anion-exchange chromatographies. Based on internal amino acid sequence analysis and different mobilities obtained with non-denaturing polyacrylamide gel electrophoresis, the 106 kDa aminopeptidase is distinct from a previously described 115 kDa CryIAc-binding aminopeptidase. The 106 kDa protein was preferentially precipitated by CryIC relative to CryIAc toxin. The 106 kDa form, like the 115 kDa aminopeptidase, has a cross-reacting determinant typical of a cleaved glycosyl-phosphatidylinositol (GPI) anchor. On ligand blots, CryIAc recognized membrane bound 120 and soluble 115 kDa aminopeptidases, but not the soluble 106 kDa form. The results show that CryIC and CryIAc -endotoxins recognize functionally related, but structurally distinct 106 kDa and 115 kDa isoforms of aminopeptidase in the M. sexta midgut.