Crystal structure of Cry51Aa1: A potential novel insecticidal aerolysin-type β-pore-forming toxin from Bacillus thuringiensis

• Structure of full-length Bacillus thuringiensis Cry51Aa1 toxin is determined at 1.65 Å.
• Cry51Aa1 exists as monomer in the asymmetric unit but forms a crystallographic dimer.
• Cry51Aa1 is toxic to Leptinotarsa decemlineata neonates.
• Cry51Aa1 has significant structural similarity to the aerolysin-type β-PFTs.
• The glycine-rich loop revels putative transmembrane features.

The structures of several Bacillus thuringiensis (Bt) insecticidal crystal proteins have been determined by crystallographic methods and a close relationship has been explicated between specific toxicities and conserved three-dimensional architectures. In this study, as a representative of the coleopteran- and hemipteran-specific Cry51A group, the complete structure of Cry51Aa1 protoxin has been determined by X-ray crystallography at 1.65 Å resolution. This is the first report of a coleopteran-active Bt insecticidal toxin with high structural similarity to the aerolysin-type β-pore forming toxins (β-PFTs). Moreover, study of featured residues and structural elements reveal their possible roles in receptor binding and pore formation events. This study provides new insights into the action of aerolysin-type β-PFTs from a structural perspective, and could be useful for the control of coleopteran and hemipteran insect pests in agricultures.