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.
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 (Mg(2+), Ca(2+) and Ba(2+)) and anions (SO(4)(2-) 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.
Kirouac
Martin
M
Groupe de Recherche en Transport Membranaire, Université de Montréal, Montreal, QC, Canada.
Vachon
Vincent
V
Noël
Jean-François
JF
Girard
Frédéric
F
Schwartz
Jean-Louis
JL
Laprade
Raynald
R
D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D000838:Anions / Q000737:chemistry; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry*; D001427:Bacterial Toxins / Q000737:chemistry; D002413:Cations, Divalent / Q000737:chemistry; D004731:Endotoxins / Q000737:chemistry*; D006460:Hemolysin Proteins; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007306:Insecticides; D007422:Intestines / Q000737:chemistry; D018402:Manduca / Q000737:chemistry*; D008871:Microvilli / Q000737:chemistry; D010539:Permeability
D000596:Amino Acids; D000838:Anions; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002413:Cations, Divalent; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis