Detection of minimum activity fragment of a novel Cry7Ab3 protein specific to Henosepilachna vigintioctomaculata (Coleopteran: Coccinellidae).

Bacillus thuringiensis Cry7Ab3 toxin has insecticidal activity against larvae of Henosepilachna vigintioctomaculata. Cry7Ab3 toxin is solubilized under alkaline condition and activated by proteases within the larval gut. In order to assess the functions of the N- and C-terminal regions, several N- and C-terminal truncated forms of Cry7Ab3 were constructed. It was determined that amino acid removal at the N-terminal, which disrupt the α-helico structure, resulted in the inactivation of the protein. The deletion of 512 amino acids from the C-terminus reduced the toxicity. However, the deletion of 481 amino acids from the C-terminus resulted in the highest activity. These findings directly demonstrated the critical roles of N- and C-terminal amino acids on the toxicity of Cry7Ab3.