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Molecular and structural characterization of a novel Cry1D toxin from Bacillus thuringiensis with high toxicity to Spodoptera littoralis (Lepidoptera: Noctuidae)

BenFarhat-Touzri, Dalel, Jemli, Sonia, Driss, Fatma, Tounsi, Slim
International journal of biological macromolecules 2019 v.126 pp. 969-976
Bacillus thuringiensis, Spodoptera littoralis, Western blotting, amino acids, genes, insecticidal properties, insecticidal proteins, juices, lethal concentration 50, midgut, molecular weight, open reading frames, pest control, polyacrylamide gel electrophoresis, proteolysis, toxicity
The investigation of new Bacillus thuringiensis (Bt) insecticidal proteins (Cry) with specific toxicity is one of the alternative measures used for Lepidopteran pest control. In the present study, a new Cry toxin was identified from a promising Bt strain BLB250 which was previously selected for its high toxicity against Spodoptera littoralis. The corresponding gene, designated cry1D-250, was cloned. It showed an ORF of 3498bp, encoding a protein of 1165 amino acid residues with a putative molecular mass of 132kDa which was confirmed by SDS-PAGE and Western blot analyses. The corresponding toxin named Cry1D-250 showed a higher insecticidal activity towards S. littoralis than Cry1D-133 (LC50 of 224.4ngcm−2) with an LC50 of only 166ngcm−2. Besides to the 65kDa active toxin, proteolysis activation of Cry1D-133 protein with S. littoralis midgut juice generated an extra form of 56kDa, which was the result of a second cleavage. Via activation study and 3D structure analysis, novel substitutions found in the Cry1D-250 protein compared to Cry1D-133 toxin were shown to be involved in the protein stability and toxicity. Therefore, the Cry1D-250 toxin can be considered to be an effective alternative for the control of S. littoralis.