Kinetic Properties of the Channels Formed by the Bacillus thuringiensis Insecticidal Crystal Protein Cry1C in the Plasma Membrane of Sf9 Cells |
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Authors: | G Guihard V Vachon R Laprade JL Schwartz |
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Institution: | (1) Biotechnology Research Institute, National Research Council, 6100 Royalmount Ave., Montreal, Quebec, H4P 2R2, Canada, CA;(2) Groupe de recherche en transport membranaire, Université de Montréal, Montréal, Quebec, H3C 3J7, Canada, CA |
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Abstract: | Spectrofluorimetric measurements were conducted to quantify, in real-time, membrane permeability changes resulting from the
treatment of Sf9 insect cells (Spodoptera frugiperda, Lepidoptera) with different Bacillus thuringiensis Cry insecticidal proteins. Coumarin-derived CD222 and Merocyanin-540 probes were respectively used to monitor extracellular
K+ and membrane potential variations upon Sf9 cells incubation with Cry toxins. Our results establish that Cry1C induces, after
a delay, the depolarization of the cell membrane and the full depletion of intracellular K+. These changes were not observed upon Sf9 cells treated with Cry1A family toxins. Both the rate of the K+ efflux and the delay before its onset were dependent on toxin concentration. Both parameters were sensitive to temperature
but only the delay was affected by pH. Cry1C-induced K+ efflux was inhibited by lanthanum ions in a dose-dependent manner. This study provides the first kinetic and quantitative
characterization of the ion fluxes through the channels formed by a Cry toxin in the plasma membrane of a susceptible insect
cell line.
Received: 4 October 1999/Revised: 21 December 1999 |
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Keywords: | :Bacillus thuringiensis— Sf9 cells — Pore-forming toxin — Intracellular K+— Ion channel |
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