Exposure of helices α4‐α5 is required for insecticidal activity of Cry2Ab by promoting assembly of a pre‐pore oligomeric structure

Abstract Cry2Ab, a pore‐forming toxin (PFT) derived from Bacillus thuringiensis (Bt), is widely used as a bio‐insecticides to control lepidopteran pests around the world. A previous study revealed that proteolytic activation of Cry2Ab by Plutella xylostella midgut juice (PxMJ) was essential for its insecticidal activity against P. xylostella, although the exact molecular mechanism remained unknown. Here we demonstrated for the first time that proteolysis of Cry2Ab uncovered an active region (the helices α4‐α5 in Domain I), which was required for the mode of action of Cry2Ab. Either the masking or the removal of helices α4‐α5 mediated the pesticidal activity of Cry2Ab. The exposure of helices α4‐α5 did not facilitate the binding of Cry2Ab to P. xylostella midgut receptors but did induce Cry2Ab monomer to aggregate and assemble a 250 kDa pre‐pore oligomer. Site‐directed mutagenesis assay was performed to generate Cry2Ab mutants site‐directed on the helices α4‐α5, and bioassays suggested that some Cry2Ab variants that could not form oligomers had significantly lower their toxicities against P. xylostella. Taken together, our data highlight the importance of helices α4‐α5 in the mode of action of Cry2Ab and could lead to more detailed studies on the insecticidal activity of Cry2Ab.
Source: Cellular Microbiology - Category: Microbiology Authors: Tags: RESEARCH ARTICLE Source Type: research