Role of helix 3 in pore formation by the Bacillus thuringiensis insecticidal toxin Cry1Aa

Vachon Vincent, Préfontaine Gabrielle, Coux Florence, Rang Cécile, Marceau Lucie, Masson Luke, Brousseau Roland, Frutos Roger, Schwartz Jean Louis, Laprade Raynald. 2002. Role of helix 3 in pore formation by the Bacillus thuringiensis insecticidal toxin Cry1Aa. Biochemistry, 41 : 6178-6184.

Résumé : Helix 3 of the Cry1Aa toxin from Bacillus thuringiensis possesses eight charged amino acids. These residues, with the exception of those involved in intramolecular salt bridges (E90, R93, E112, and R115), were mutated individually either to a neutral or to an oppositely charged amino acid. The mutated genes were expressed, and the resultant, trypsin-activated toxins were assessed for their toxicity to Manduca sexta larvae and their ability to permeabilize M. sexta larval midgut brush border membrane vesicles to KCI, sucrose, raffinose, potassium gluconate, and N-methyl-D-glucamine hydrochloride with a lightscattering assay based on osmotic swelling. Most mutants were considerably less toxic than Cry1Aa. Replacing either E101, E116, E118, or D120 by cysteine, glutamine, or lysine residues had only minor effects on the properties of the pores formed by the modified toxins. However, half of these mutants (E101C, E101Q, E101K, E116K, E118C, and D120K) had a significantly slower rate of pore formation than Cry1Aa. Mutations at R99 (R99C, R99E, and R99Y) resulted in an almost complete loss of poreforming ability. These results are consistent with a model in which x-helix 3 plays an important role in the mechanism of pore formation without being directly involved in determining the properties of the pores.

Mots-clés Agrovoc : Bacillus thuringiensis, lutte anti-insecte, toxine bactérienne

Classification Agris : H10 - Ravageurs des plantes

Auteurs et affiliations

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

Source : Cirad - Agritrop (https://agritrop.cirad.fr/507361/)

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