title: Analysis of the molecular basis of insecticidal specificity of Bacillus thuringiensis crystal delta-endotoxin.
abstract: The mechanism of action and receptor binding of a dual-specificity Bacillus thuringiensis var. aizawai ICl delta-endotoxin was studied using insect cell culture. The native protoxin was labelled with 125I, proteolytically activated and the affinity of the resulting preparations for insect cell-membrane proteins was studied by blotting. The active preparations obtained by various treatments had characteristic specificity associated with unique polypeptides, and showed affinity for different membrane proteins. The lepidopteran-specific preparation (trypsin-treated protoxin containing 58 and 55 kDa polypeptides) bound to two membrane proteins in the lepidopteran cells but none in the dipteran cells. The dipteran-specific preparation (protoxin treated sequentially with trypsin and Aedes aegypti gut proteases, containing a 53 kDa polypeptide) bound to a 90 kDa membrane protein in the dipteran (A. aegypti) cells but bound to none in the lepidopteran cells or Drosophila melanogaster cells. The toxicity of trypsin-activated delta-endotoxin was completely inhibited by preincubation with D-glucose, suggesting a role for this carbohydrate in toxin-receptor interaction. The toxicity was also decreased by osmotic protectants to an extent proportional to their viscometric radius. These results support a proposal that initial interaction of toxin with a unique receptor determines the specificity of the toxin, following which cell death occurs by a mechanism of colloid osmotic lysis.
authors.affiliation: Department of Biochemistry, University of Cambridge, U.K.
authors.forename: M Z
authors.initials: MZ
authors.lastname: Haider
authors.forename: D J
authors.initials: DJ
authors.lastname: Ellar
mesh_terms: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002241:Carbohydrates / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003208:Concanavalin A / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004731:Endotoxins / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology; D006460:Hemolysin Proteins; D007306:Insecticides / Q000494:pharmacology*; D010944:Plants; D011971:Receptors, Immunologic / Q000378:metabolism; D013045:Species Specificity
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002241:Carbohydrates; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; D011971:Receptors, Immunologic; C048071:endotoxin receptor; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D003208:Concanavalin A; D005947:Glucose