Binding of Bacillus thuringiensis Cry1A toxins to brush border membrane vesicles of midgut from Cry1Ac susceptible and resistant Plutella xylostella

Current models of the mode of action of Bacillus thuringiensis insecticidal crystal proteins: A critical review

“…The sequential binding model is particularly attractive in that it tentatively explains why alterations in the binding properties or the level of expression of either cadherins (Gahan et al, 2001;Morin et al, 2003;Xu et al, 2005) or aminopeptidases N (Zhang et al, 2009) can alone result in high levels of resistance to Bt toxins even if some cases of resistance do not appear to be attributable to modifications in either one of these receptors (Baxter et al, 2005(Baxter et al, , 2008Gahan et al, 2010;Higuchi et al, 2007;Khajuria et al, 2011). Similarly, RNA silencing of either the cadherin (Fabrick et al, 2009;Soberón et al, 2007b) or the aminopeptidase (Rajagopal et al, 2002;Sivakumar et al, 2007) genes alone can cause resistance to Cry toxins.…”

The Elimination of DNA from the Cry Toxin-DNA Complex Is a Necessary Step in the Mode of Action of the Cry8 Toxin

“…After removal of the DNA from the toxin-DNA complex by DNase I, the Cry8Ea1 toxin specifically bound to its target in the midgut of the insect. Many studies have focused on the interaction of the Cry toxin with insect BBMVs, and most have shown that the Cry toxin interacts with BBMVs specifically, with clear competition of the unlabeled toxin with the toxin-binding sites using standard methods; however, these methods do not account for bound DNA nor make any provision for removing DNA [25]–[31]. In our previous research, no DNA could be detected in the toxin obtained in the main elution peak from the Resource-Q column before or after phenol/chloroform extraction (Fig.…”

“…2A). In the other studies, the Cry toxin was purified by anion-exchange chromatography [25]–[31], and thus the obtained Cry toxin might also be lacking DNA.…”

Investigation of physicochemical condition to stabilize phosphatidylcholine-liposome enclosing fluorescent calcein and its exploitation for analysis of pore formation with Cry1A toxins of Bacillus thuringiensis

“…Crystals of B. thuringiensis culture in 200 ml culture media were isolated and solubilized as in Higuchi et al (2007). The Cry1Ab produced in E. coli was solubilized as in Höfte et al (1986) and Lee et al (1992).…”

“…We are maintaining Cry1Ac-resistant Plutella xylostella L. (Lepidoptera: Yponomeutidae) (PXR) in the laboratory and they show 100,000 times resistance to Cry1Ac than a susceptible strain (PXS) (Kato et al, 2006); however, Cry1Ac was shown to bind the brush border membrane vesicle (BBMV) from both PXR and PXS midguts with almost equal K d values of ϳ200 nM (Higuchi et al, 2007) and detergent-soluble BBMV proteins from both strains (Kato et al, 2006). If this is true, it obviously argues that actual resistance exists, either in the insertion step of toxin molecules into the plasma membrane or in the final pore-formation step; however, providing evidence to support this theory is not straightforward as various binding proteins exist on the membrane.…”