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Applied and Environmental Microbiology, November 2002, p. 5711-5717, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5711-5717.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Altered Glycosylation of 63- and 68-Kilodalton Microvillar Proteins in Heliothis virescens Correlates with Reduced Cry1 Toxin Binding, Decreased Pore Formation, and Increased Resistance to Bacillus thuringiensis Cry1 Toxins

Juan Luis Jurat-Fuentes,1 Fred L. Gould,2 and Michael J. Adang1,3*

Departments of Entomology,1 Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602-2603,3 Department of Entomology, North Carolina State University, Raleigh, North Carolina 276952

Received 3 April 2002/ Accepted 19 August 2002

The binding and pore formation abilities of Cry1A and Cry1Fa Bacillus thuringiensis toxins were analyzed by using brush border membrane vesicles (BBMV) prepared from sensitive (YDK) and resistant (YHD2) strains of Heliothis virescens. 125I-labeled Cry1Aa, Cry1Ab, and Cry1Ac toxins did not bind to BBMV from the resistant YHD2 strain, while specific binding to sensitive YDK vesicles was observed. Binding assays revealed a reduction in Cry1Fa binding to BBMV from resistant larvae compared to Cry1Fa binding to BBMV from sensitive larvae. In agreement with this reduction in binding, neither Cry1A nor Cry1Fa toxin altered the permeability of membrane vesicles from resistant larvae, as measured by a light-scattering assay. Ligand blotting experiments performed with BBMV and 125I-Cry1Ac did not differentiate sensitive larvae from resistant larvae. Iodination of BBMV surface proteins suggested that putative toxin-binding proteins were exposed on the surface of the BBMV from resistant insects. BBMV protein blots probed with the N-acetylgalactosamine-specific lectin soybean agglutinin (SBA) revealed altered glycosylation of 63- and 68-kDa glycoproteins but not altered glycosylation of known Cry1 toxin-binding proteins in YHD2 BBMV. The F1 progeny of crosses between sensitive and resistant insects were similar to the sensitive strain when they were tested by toxin-binding assays, light-scattering assays, and lectin blotting with SBA. These results are evidence that a dramatic reduction in toxin binding is responsible for the increased resistance and cross-resistance to Cry1 toxins observed in the YHD2 strain of H. virescens and that this trait correlates with altered glycosylation of specific brush border membrane glycoproteins.


* Corresponding author. Mailing address: Department of Entomology, University of Georgia, Athens, GA 30602-2603. Phone: (706) 542-2436. Fax: (706) 542-2279. E-mail: adang{at}arches.uga.edu.


Applied and Environmental Microbiology, November 2002, p. 5711-5717, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5711-5717.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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