Kinetics of pore formation by the Bacillus thuringiensis toxin Cry1Ac.
After binding to specific receptors, Cry toxins form pores in the midgut apical membrane of susceptible insects. The receptors could form part of the pore structure or simply catalyze pore formation and consequently be recycled. To discriminate between these possibilities, the kinetics of pore formation in brush border membrane vesicles isolated from Manduca sexta was studied with an osmotic swelling assay. Pore formation, as deduced from changes in membrane permeability induced by Cry1Ac during a 60-min incubation period, was strongly dose-dependent, but rapidly reached a maximum as toxin concentration was increased. Following exposure of the vesicles to the toxin, the osmotic swelling rate reached a maximum shortly after a delay period. Under these conditions, at relatively high toxin concentrations, the maximal osmotic swelling rate increased linearly with toxin concentration. When vesicles were incubated for a short time with the toxin and then rapidly cooled to prevent the formation of new pores before and during the osmotic swelling experiment, a plateau in the rate of pore formation was observed as toxin concentration was increased. Taken together, these results suggest that the receptors do not act as simple catalysts of pore formation, but remain associated with the pores once they are formed.
Fortier
Mélanie
M
Groupe d'étude des protéines membranaires, Université de Montréal, PO Box 6128, Centre Ville Station, Montreal, Quebec, Canada H3C 3J7.
Vachon
Vincent
V
Marceau
Lucie
L
Schwartz
Jean-Louis
JL
Laprade
Raynald
R
D000818:Animals; D001413:Bacillus thuringiensis / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000378:metabolism* / Q000494:pharmacology; D001427:Bacterial Toxins / Q000378:metabolism* / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D004731:Endotoxins / Q000378:metabolism* / Q000494:pharmacology; D006460:Hemolysin Proteins / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D018402:Manduca / Q000187:drug effects; D008871:Microvilli / Q000187:drug effects; D009997:Osmotic Pressure / Q000187:drug effects; D052899:Pore Forming Cytotoxic Proteins / Q000378:metabolism* / Q000494:pharmacology
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D052899:Pore Forming Cytotoxic Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis