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Applied and Environmental Microbiology, March 2008, p. 1710-1716, Vol. 74, No. 6
0099-2240/08/$08.00+0 doi:10.1128/AEM.02827-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Departamento de Genética, Facultad de CC. Biológicas, Universidad de Valencia, Valencia, Spain
Received 14 December 2007/ Accepted 16 January 2008
It is generally accepted that Bacillus thuringiensis Cry toxins insert into the apical membrane of the larval midgut after binding to specific receptors, and there is evidence that the distribution of binding molecules along the midgut is not uniform. By use of the voltage-sensitive dye DiSC3(5) and 125I-labeled Cry1Ac, we have measured the effect of Cry1Ac in terms of permeabilization capacity and of binding parameters on brush border membrane vesicles (BBMV) prepared from the anterior and the posterior regions of the larval midgut from two insect species, Manduca sexta and Helicoverpa armigera. The permeabilizing activity was significantly higher with BBMV from the posterior region than with the one observed in the anterior region in both insect species. Instead, 125I-Cry1Ac bound specifically to BBMV from the two midgut regions, with no significant differences in the binding parameters between the anterior and posterior regions within an insect species. N-acetylgalactosamine inhibition patterns on pore formation and binding differed between anterior and posterior midgut regions and between species, providing evidence of a multifaceted involvement of the sugar in the Cry1Ac mode of action. The analysis of binding and pore formation in different midgut regions could be an effective method to study differences in the mode of action of Cry1Ac toxin in different species.
Published ahead of print on 25 January 2008.
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