Common features of Bacillus thuringiensis toxins specific for Diptera and Lepidoptera.
The complete nucleotide sequence of a cloned gene encoding a 130-kDa crystal protein of Bacillus thuringiensis (B.t.) subspecies israelensis has been determined. The recombinant protein (Bt8) was purified and shown to be a mosquito-specific toxin with a LC50 value of 43 ng/ml to third-instar larvae of Aedes aegypti. Bt8 is processed by proteases or midgut extracts of mosquito larvae into toxic fragments of 68-78 kDa. Deletion mapping indicated that the active fragment of Bt8 is localized in the N-terminal half of the protoxin molecule. The deduced amino acid sequence of Bt8 has been compared with that of Bt2, a Lepidoptera-specific toxin, previously cloned from Bacillus thuringiensis berliner. Highly homologous amino acid stretches are present in the C-terminal half of the proteins. The N-terminal parts show much less sequence homology but they display a strikingly similar distribution of hydrophilic and hydrophobic amino acids. In addition, Bt8 and Bt2 show a significant immunological cross-reaction. The data indicate that although these B.t. delta endotoxins exhibit a different insect-host specificity, they are structurally related and might use a similar mechanism to interact with insect cell membranes.
Chungjatupornchai
W
W
Plant Genetic Systems, Gent, Belgium.
Höfte
H
H
Seurinck
J
J
Angsuthanasombat
C
C
Vaeck
M
M
D000330:Aedes; D000595:Amino Acid Sequence; D000818:Animals; D001413:Bacillus thuringiensis / Q000032:analysis* / Q000235:genetics; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000633:toxicity; D001427:Bacterial Toxins; D001483:Base Sequence; D003001:Cloning, Molecular; D004175:Diptera; D004731:Endotoxins / Q000235:genetics / Q000302:isolation & purification / Q000633:toxicity*; D005798:Genes, Bacterial; D006460:Hemolysin Proteins; D007915:Lepidoptera; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000633:toxicity; D013329:Structure-Activity Relationship
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D010446:Peptide Fragments; C030956:insecticidal crystal protein, Bacillus Thuringiensis