Insecticidal crystal proteins produced by strains of Bacillus thuringiensis cause larval death upon interaction with specific receptors located at the midgut epithelium of susceptible insects. Large quantities of easily purified aminopeptidase and cadherin-like Cry toxin receptors can facilitate the further study of Cry toxin binding and pore formation. Here, we report the solubilisation and purification of aminopeptidase N from Spodoptera litura (SIAPN). Recombinantly expressed and membrane anchored aminopeptidase N showed differential solubilisation with various ionic and nonionic detergents. The N-lauryl sarcosine (NLS)-solubilised SIAPN was purified to near homogeneity by anion exchange and gel filtration chromatography and refolded to its catalytically active form. The optimized purification regimen lead to > 90% purification of the catalytically active SIAPN with 11% recovery and 9-folds purification. The interaction of purified SIAPN with biologically active Cry1C protein has been qualitatively and quantitatively characterized. By ligand blotting experiment, we demonstrated the linearity of interaction of the two purified proteins and lack of interaction of SIAPN with structurally divergent nontoxic Cry1Ac protein. The equilibrium dissociation constant (KID) of purified SIAPN for Cry1C was calculated by ELISA (90 nM). Interaction of enzymatically inactive SIAPN with Cry1C and catalytic activity of APN-Cry1C complex suggested that the catalytic site and toxin-binding sites of SIAPN do not overlap. (C) 2007 Elsevier Inc. All rights reserved.