Key residues of Bacillus thuringiensis Cry2Ab for oligomerization and pore-formation activity

Zhi-Zhen Pan,Bo Liu,Qing-Xi Chen,Yu-Jing Zhu,Lian Xu

doi:10.1186/s13568-021-01270-0

Zhi-Zhen Pan, Bo Liu + Show 3 more

Open Access

https://doi.org/10.1186/s13568-021-01270-0

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Abstract

As a pore-forming toxin, activation, oligomerization and pore-formation were both required for the mode of action of Cry toxins. Previous results revealed that the helices α4–α5 of Domain I were involved in the oligomerization of Cry2Ab, however, the key residues for Cry2Ab aggregation remained ambiguous. In present studies, we built 20 Cry2Ab alanine mutants site-directed in the helices α4–α5 of Domain I and demonstrated that mutants N151A, T152A, F157A, L183A, L185A and I188A could reduce the assembly of the 250 kDa oligomers, suggesting that these mutation residues might be essential for Cry2Ab oligomerization. As expected, all of these variants showed lower insecticidal activity against P. xylostella. Furthermore, we found that the pore-forming activities of these mutants also decreased when compared to wild-type Cry2Ab. Taken together, our data identified key residues for Cry2Ab oligomerization and emphasized that oligomerization was closely related to the insecticidal activity and pore-forming activity of Cry2Ab.

Highlights

Cry toxin, an insecticidal crystal toxin derived from Bacillus thuringiensis (Bt), is widely applied as a bioinsecticides to control agricultural pests all over the world (Bravo et al 2011; Schnepf et al 1998)
We sought to determine the key residues of Cry2Ab for oligomerization activity by constructing 20 alanine mutants site directed on helices α4–α5
Cry2Ab since some Cry2Ab mutants (TM152153AA, LF156157AA, NR159160AA, LH183184AA, FI187188AA) failed to assemble 250 kDa oligomers (Fig. 1A). Those results suggested that the active regions for Cry2Ab oligomerization might limited to V 150-R160 in helix α-4 and N182-D190 in helix α-5 (Fig. 1B)

Summary

Introduction

An insecticidal crystal toxin derived from Bacillus thuringiensis (Bt), is widely applied as a bioinsecticides to control agricultural pests all over the world (Bravo et al 2011; Schnepf et al 1998). A number of insect midgut proteins such as cadherin, aminopeptidase-N (APN), alkaline phosphatase (ALP) and ATP-binding cassette transporter subfamily C member 2 (ABCC2) have been proposed as functional receptors and mediated the insecticidal activities of Cry toxins (Pigott and Ellar 2007; Zhou et al 2017; Park et al 2009; Guo et al 2015; Chen et al 2017). It was reported that the improper processing of Cry toxins was associated with Cry resistance in lepidopteran insects (Liu et al 2014; Xia et al 2016). Those studies made a closer look on the mechanism of Cry toxins and provided new strategies for agricultural pest control

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