Helix 4 mutants of the Bacillus thuringiensis insecticidal toxin Cry1Aa display altered pore-forming abilities

Vachon Vincent, Préfontaine Gabrielle, Rang Cécile, Coux Florence, Juteau Marc, Schwartz Jean Louis, Brousseau Roland, Frutos Roger, Laprade Raynald, Masson Luc. 2004. Helix 4 mutants of the Bacillus thuringiensis insecticidal toxin Cry1Aa display altered pore-forming abilities. Applied and Environmental Microbiology, 70 (10) : 6123-6130.

Résumé : The role played by [alpha]-helix 4 of the Bacillus thuringiensis toxin Cry1Aa in pore formation was investigated by individually replacing each of its charged residues with either a neutral or an oppositely charged amino acid by using site-directed mutagenesis. The majority of the resulting mutant proteins were considerably less toxic to Manduca sexta larvae than Cry1Aa. Most mutants also had a considerably reduced ability to form pores in midgut brush border membrane vesicles isolated from this insect, with the notable exception of those with alterations at amino acid position 127 (R127N and R127E), located near the N-terminal end of the helix. Introducing a negatively charged amino acid near the C-terminal end of the helix (T142D and T143D), a region normally devoid of charged residues, completely abolished pore formation. For each mutant that retained detectable pore-forming activity, reduced membrane permeability to KCl was accompanied by an approximately equivalent reduction in permeability to N-methyl-D-glucamine hydrochloride, potassium gluconate, sucrose, and raffinose and by a reduced rate of pore formation. These results indicate that the main effect of the mutations was to decrease the toxin's ability to form pores. They provide further evidence that -helix 4 plays a crucial role in the mechanism of pore formation.

Classification Agris : F30 - Génétique et amélioration des plantes

Auteurs et affiliations

• Vachon Vincent, Université de Montréal (CAN)
• Préfontaine Gabrielle, National Research Council (CAN)
• Rang Cécile, CIRAD-AMIS-BIOTROP (FRA)
• Coux Florence, Université de Montréal (CAN)
• Juteau Marc, Université de Montréal (CAN)
• Schwartz Jean Louis, Université de Montréal (CAN)
• Brousseau Roland, Biotechnology Research Institute (CAN)
• Frutos Roger, CIRAD-AMIS-PROTECTION DES CULTURES (FRA)
• Laprade Raynald, Université de Montréal (CAN)
• Masson Luc, National Research Council (CAN)

Source : Cirad - Agritrop (https://agritrop.cirad.fr/542067/)

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