Amino acid and divalent ion permeability of the pores formed by the Bacillus thuringiensis toxins Cry1Aa and Cry1Ac in insect midgut brush border membrane vesicles |
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Authors: | Martin KirouacVincent Vachon,Jean-Franç ois Noë lFré dé ric Girard,Jean-Louis Schwartz,Raynald Laprade |
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Affiliation: | a Groupe de Recherche en Transport Membranaire, Université de Montréal, P.O. Box 6128, Centre Ville Station, Montreal, QC, Canada H3C 3J7 b Biotechnology Research Institute, National Research Council, 6100 Royalmount Avenue, Montreal, QC, Canada H4P 2R2 |
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Abstract: | The pores formed by Bacillus thuringiensis insecticidal toxins have been shown to allow the diffusion of a variety of monovalent cations and anions and neutral solutes. To further characterize their ion selectivity, membrane permeability induced by Cry1Aa and Cry1Ac to amino acids (Asp, Glu, Ser, Leu, His, Lys and Arg) and to divalent cations (Mg2+, Ca2+ and Ba2+) and anions (SO42− and phosphate) was analyzed at pH 7.5 and 10.5 with midgut brush border membrane vesicles isolated from Manduca sexta and an osmotic swelling assay. Shifting pH from 7.5 to 10.5 increases the proportion of the more negatively charged species of amino acids and phosphate ions. All amino acids diffused well across the toxin-induced pores, but, except for aspartate and glutamate, amino acid permeability was lower at the higher pH. In the presence of either toxin, membrane permeability was higher for the chloride salts of divalent cations than for the potassium salts of divalent anions. These results clearly indicate that the pores are cation-selective. |
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Keywords: | Insecticidal toxin Ion selectivity Membrane permeability Brush border membrane vesicle Bacillus thuringiensis Manduca sexta |
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