Leucine transport is affected by Bacillus thuringiensis Cry1 toxins in brush border membrane vesicles from Ostrinia nubilalis Hb (Lepidoptera: Pyralidae) and Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae) midgut.
The pore-forming activity of Cry1Ab, Cry1Fa and Cry1Ca toxins and their interaction with leucine transport mediated by the K(+)/leucine cotransporter were studied in brush border membrane vesicles (BBMVs) isolated from the midgut of Ostrinia nubilalis and Sesamia nonagrioides. In both species, as in other Lepidoptera, leucine uptake by BBMVs can take place in the absence of cations, but it can also be driven by a K(+) gradient. Experiments with the voltage-sensitive fluorescent dye 3,3'-diethylthiacarbocyanine iodide proved that Cry1Ab, a Bacillus thuringiensis toxin active in vivo, enhanced the membrane permeability to potassium in O. nubilalis BBMVs. This result is in agreement with similar effects observed in S. nonagrioides BBMV incubated with various Cry1 toxins active in vivo. The effect of the above toxins was tested on the initial rate of 0.1 mM: leucine influx. Instead of an increase in leucine influx, a reduction was observed with the Cry1 toxins active in vivo. Cry1Ab and Cry1Fa, but not the inactive toxin Cry1Da, inhibited in a dose-dependent manner leucine uptake both in the absence and in the presence of a K(+) gradient, a clear indication that their effect is independent of the channel formed by the toxins and that this effect is exerted directly on the amino acid transport system.
Leonardi
M Giovanna
MG
Dipartimento di Biologia, Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy MGiovanna.Leonardi@unimi.it
Caccia
Silvia
S
González-Cabrera
Joel
J
Ferré
Juan
J
Giordana
Barbara
B
D000818:Animals; D001413:Bacillus thuringiensis / Q000737:chemistry*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000737:chemistry / Q000494:pharmacology*; D052160:Benzothiazoles / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002232:Carbocyanines / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D004731:Endotoxins / Q000737:chemistry / Q000494:pharmacology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D006460:Hemolysin Proteins / Q000737:chemistry / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000378:metabolism; D007814:Larva / Q000378:metabolism; D007915:Lepidoptera / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D022161:Transport Vesicles / Q000378:metabolism*
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D052160:Benzothiazoles; D002232:Carbocyanines; D004731:Endotoxins; D005456:Fluorescent Dyes; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; C072030:3,3'-diethylthiacarbocyanine iodide; D007930:Leucine; D011188:Potassium