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Journal of Bacteriology, May 2006, p. 3391-3401, Vol. 188, No. 9
0021-9193/06/$08.00+0     doi:10.1128/JB.188.9.3391-3401.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Structure of the Functional Form of the Mosquito Larvicidal Cry4Aa Toxin from Bacillus thuringiensis at a 2.8-Angstrom Resolution

Panadda Boonserm,1* Min Mo,2 Chanan Angsuthanasombat,1 and Julien Lescar2*

Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand,1 School of Biological Sciences, Nanyang Technological University, 60, Nanyang Drive, Singapore 6375512

Received 2 December 2005/ Accepted 23 January 2006

The Cry4Aa {delta}-endotoxin from Bacillus thuringiensis is toxic to larvae of Culex, Anopheles, and Aedes mosquitoes, which are vectors of important human tropical diseases. With the objective of designing modified toxins with improved potency that could be used as biopesticides, we determined the structure of this toxin in its functional form at a resolution of 2.8 Å. Like other Cry {delta}-endotoxins, the activated Cry4Aa toxin consists of three globular domains, a seven-{alpha}-helix bundle responsible for pore formation (domain I) and the following two other domains having structural similarities with carbohydrate binding proteins: a ß-prism (domain II) and a plant lectin-like ß-sandwich (domain III). We also studied the effect on toxicity of amino acid substitutions and deletions in three loops located at the surface of the putative receptor binding domain II of Cry4Aa. Our results indicate that one loop is an important determinant of toxicity, presumably through attachment of Cry4Aa to the surface of mosquito cells. The availability of the Cry4Aa structure should guide further investigations aimed at the molecular basis of the target specificity and membrane insertion of Cry endotoxins.

* Corresponding author. Mailing address for Panadda Boonserm: Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand. Phone: (66) 2800 3624. Fax: (66) 2441 9906. E-mail: mbpbs{at}mahidol.ac.th. Mailing address for Julien Lescar: School of Biological Sciences, Nanyang Technological University, 60, Nanyang Drive, Singapore 637551. Phone: (65) 6316 2859. Fax: (65) 6791 3856. E-mail: julien{at}ntu.edu.sg.

Journal of Bacteriology, May 2006, p. 3391-3401, Vol. 188, No. 9
0021-9193/06/$08.00+0     doi:10.1128/JB.188.9.3391-3401.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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