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Appl. Environ. Microbiol., 05 1996, 1537-1543, Vol 62, No. 5
RA de Maagd, MS Kwa, H van der Klei, T Yamamoto, B Schipper, JM Vlak, WJ Stiekema and D Bosch
To test our hypothesis that substitution of domain III of Bacillus
thuringiensis delta-endotoxin (Cry) proteins might improve toxicity to pest
insects, e.g., Spodoptera exigua, in vivo recombination was used to produce
a number of cryIA(b)-cryIC hybrid genes. A rapid screening assay was
subsequently exploited to select hybrid genes encoding soluble protoxins.
Screening of 120 recombinants yielded two different hybrid genes encoding
soluble proteins with domains I and II of CryIA(b) and domain III of CryIC.
These proteins differed by only one amino acid residue. Both hybrid
protoxins gave a protease-resistant toxin upon in vitro activation by
trypsin. Bioassays showed that one of these CryIA(b)-CryIC hybrid proteins
(H04) was highly toxic to S. exigua compared with the parental CryIA(b)
protein and significantly more toxic than CryIC. In semiquantitative
binding studies with biotin- labelled toxins and intact brush border
membrane vesicles of S. exigua, this domain III substitution appeared not
to affect binding-site specificity. However, binding to a 200-kDa protein
by CryIA(b) in preparations of solubilized and blotted brush border
membrane vesicle proteins was completely abolished by the domain III
substitution. A reciprocal hybrid containing domains I and II of CryIC and
domain III of CryIA(b) did bind to the 200-kDa protein, confirming that
domain III of CryIA(b) was essential for this reaction. These results show
that domain III of CryIC protein plays an important role in the level of
toxicity to S. exigua, that substitution of domain III may be a powerful
tool to increase the repertoire of available active toxins for pest
insects, and that domain III is involved in binding to gut epithelium
membrane proteins of S. exigua.
Copyright © 1996, American Society for Microbiology
Domain III substitution in Bacillus thuringiensis delta-endotoxin CryIA(b) results in superior toxicity for Spodoptera exigua and altered membrane protein recognition
Department of Molecular Biology, Centre for Plant Breeding and Reproduction Research, Wageningen, The Netherlands. R.A.deMaagd@CPRO.DLO.NL
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