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Applied and Environmental Microbiology, December 2001, p. 5715-5720, Vol. 67, No. 12
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.12.5715-5720.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

The alpha -Helix 4 Residue, Asn135, Is Involved in the Oligomerization of Cry1Ac1 and Cry1Ab5 Bacillus thuringiensis Toxins

Natalie J. Tigue,* Juliette Jacoby, and David J. Ellar

Department of Biochemistry, Cambridge University, Cambridge CB2 1GA, United Kingdom

Received 6 August 2001/Accepted 2 October 2001

The insecticidal Cry toxins produced by the bacterium Bacillus thuringiensis are comprised of three structural domains. Domain I, a seven-helix bundle, is thought to penetrate the insect epithelial cell plasma membrane through a hairpin composed of alpha -helices 4 and 5, followed by the oligomerization of four hairpin monomers. The alpha -helix 4 has been proposed to line the lumen of the pore, whereas some residues in alpha -helix 5 have been shown to be responsible for oligomerization. Mutation of the Cry1Ac1 alpha -helix 4 amino acid Asn135 to Gln resulted in the loss of toxicity to Manduca sexta, yet binding was still observed. In this study, the equivalent mutation was made in the Cry1Ab5 toxin, and the properties of both wild-type and mutant toxin counterparts were analyzed. Both mutants appeared to bind to M. sexta membrane vesicles, but they were not able to form pores. The ability of both N135Q mutants to oligomerize was also disrupted, providing the first evidence that a residue in alpha -helix 4 can contribute to toxin oligomerization.

* Corresponding author. Present address: Molecular Biology Department, GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex CM19 5AW, United Kingdom. Phone: 44 (0)1279 627019. Fax: 44 (0)1279 627266. E-mail: Natalie_J_Tigue{at}sbphrd.com.

Applied and Environmental Microbiology, December 2001, p. 5715-5720, Vol. 67, No. 12
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.12.5715-5720.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.