Insecticidal activities of Bacillus thurigiensis Cry toxins relied on their interaction with the midgut receptors inlaying in the brush border membrane vesicles(BBMV)of target insects.In the present study,we demonstrated that an aminopeptidase N(PxAPN5)mediated the insecticidal action of Cry2Ab in Plutella xylostella(L.).Silence of PxAPN5 in P xylostella larvae greatly reduced their susceptibility to Cry2Ab and led to a decrease of Cry2Ab binding to P.xylostella BBMV.Those findings highlighted the role of PxAPN5 in mode of action of Cry2Ab toxins.Furthermore,the PxAPN5-binding region of Cry2Ab was evaluated by expressing truncated domains of PxAPN5 and detecting their binding abilities to Cry2Ab using ligand blot.The results suggested that D1 domain(residues 1-260)and D3 domain(residues 510-620)of PxAPN5 could specially bind to Cry2Ab.Our findings firstly demonstrated that PxAPN5 played an essential role in the action of Cry2Ab in P xylostella and provided new insight into the Cry-receptors interactions.