Specificity of Bacillus thuringiensis delta-endotoxins is correlated with the presence of high-affinity binding sites in the brush border membrane of target insect midguts

• Published in: Proceedings of the National Academy of Sciences - PNAS 1988-11, Vol.85 (21), p.7844-7848
• Main Authors: Hofmann, C, Vanderbruggen, H, Hofte, H, Rie, J. van, Jansens, S, Mellaert, H. van
• Format: Article
• Language: English
• Subjects: Animal Population Groups; BACILLUS THURINGIENSIS; Bacterial Proteins; Bacterial Toxins; Bacteriology; Binding Sites; Binding, Competitive; Biological and medical sciences; Brush border membrane vesicles; brush border membranes; Butterflies - metabolism; delta -endotoxin; ENDOTOXINAS; ENDOTOXINE; ENDOTOXINS; Endotoxins - metabolism; Endotoxins - toxicity; Fundamental and applied biological sciences. Psychology; Hemolysin Proteins; Insect larvae; INSECTICIDAS; INSECTICIDE; INSECTICIDES; INTESTIN; INTESTINES; INTESTINOS; IODE; IODINE; ISOTOPE LABELLING; Larva - metabolism; LARVAE; LARVAS; LARVE; Lepidoptera - metabolism; MANDUCA; MANDUCA SEXTA; MARCACION CON ISOTOPOS; MARQUAGE ISOTOPIQUE; Microbiology; Microvilli; Microvilli - metabolism; Midgut; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Pieridae; PIERIS; PIERIS (INSECT); Pieris brassicae; Receptors; Serum albumins; Sphingidae; TOXICIDAD; TOXICITE; TOXICITY; Toxins; YODO
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.85.21.7844

Binding studies were performed with two 125I-labeled Bacillus thuringiensis δ -endotoxins on brush border membrane vesicles prepared from the larval midgut of the tobacco hornworm Manduca sexta or the cabbage butterfly Pieris brassicae. One δ -endotoxin, Bt2-protoxin, is a 130-kDa recombinant crystalline protein from B. thuringiensis subsp. berliner. It kills larvae of both insect species. The active Bt2-toxin is a 60-kDa proteolytic fragment of the Bt2-protoxin. It binds saturably and with high affinity to brush border membrane vesicles from the midgut of both species. The other δ -endotoxin, Bt4412-protoxin, is a 136-kDa crystalline protein from B. thuringiensis subsp. thuringiensis, which is highly toxic for P. brassicae, but not for M. sexta larvae. Bt4412-toxin, obtained after proteolytic activation of Bt4412-protoxin, shows high-affinity saturable binding to P. brassicae vesicles but not to M. sexta vesicles. The correlation between toxicity and specific binding is further strengthened by competition studies. Other B. thuringiensis δ -endotoxins active against M. sexta compete for binding of 125I-labeled Bt2-toxin to M. sexta vesicles, whereas toxins active against dipteran or coleopteran larvae do not compete. Bt2-toxin and Bt4412-toxin bind to different sites on P. brassicae vesicles.