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The pre-pore from Bacillus thuringiensis Cry1Ab toxin is necessary to induce insect death in Manduca sexta - PubMed

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The pre-pore from Bacillus thuringiensis Cry1Ab toxin is necessary to induce insect death in Manduca sexta

N Jiménez-Juárez et al. Peptides. 2008 Feb.

Abstract

The insecticidal Cry toxins from Bacillus thuringiensis bacteria are pore-forming toxins that lyse midgut epithelial cells in insects. We have previously proposed that they form pre-pore oligomeric intermediates before membrane insertion. For formation of these oligomers coiled-coil structures are important, and helix alpha-3 from Cry toxins could form coiled-coils. Our data shows that different mutations in helix alpha-3 are affected in pore formation and toxicity. Mutants affected in toxicity bind Bt-R(1) receptor with a similar K(D) as the wild type toxin but do not form oligomers nor induce pore formation in planar lipid bilayers, indicating that the pre-pore oligomer is an obligate intermediate in the intoxication of Cry1Ab toxin and that interaction of monomeric Cry1Ab with Bt-R(1) is not enough to kill susceptible larvae.

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Figures

Figure 1
Figure 1. Analysis of coiled coil structures in Cry toxins

Panel A, Schematic representation of the putative coiled-coil structures of helix α-3 from different Cry toxins. The position of residues a, b, c, d, e, f and g of the heptad and the conserved amino acid residues located in positions a and d are shown. Panel B, Alignment of the amino acid sequence corresponding to helix α-3 of different Cry toxins. Green letters correspond to hydrophobic amino acid residues; blue to positively charged residues and pink to polar amino acids.

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