Affiliation:
1. Plant Genetic Systems, J. Plateaustraat 22, and Laboratorium voor Agrozoölogie, 2 B-9000 Ghent, Belgium
Abstract
Binding of three
Bacillus thuringiensis
insecticidal crystal proteins (ICPs) to the midgut epithelium of
Ostrinia nubilalis
larvae was characterized by performing binding experiments with both isolated brush border membrane vesicles and gut tissue sections. Our results demonstrate that two independent ICP receptors are present in the brush border of
O. nubilalis
gut epithelium. From competition binding experiments performed with
125
I-labeled and native ICPs it was concluded that CryIA(b) and CryIA(c) are recognized by the same receptor. An 11-fold-higher binding affinity of CryIA(b) for this receptor correlated with a 10-fold-higher toxicity of this ICP compared with CryIA(c). The CryIB toxin did not compete for the binding site of CryIA(b) and CryIA(c). Immunological detection of ingested
B. thuringiensis
ICPs on gut sections of
O. nubilalis
larvae revealed binding only along the epithelial brush border membrane. CryID and CryIE, two ICPs that are not toxic to
O. nubilalis,
were not bound to the apical microvilli of gut epithelial cells. In vitro binding experiments performed with native and biotinylated ICPs on tissue sections confirmed the correlation between ICP binding and toxicity. Moreover, by performing heterologous competition experiments with biotinylated and native ICPs, it was confirmed that the CryIB receptor is different from the receptor for CryIA(b) and CryIA(c). Retention of activated crystal proteins by the peritrophic membrane was not correlated with toxicity. Furthermore, it was demonstrated that CryIA(b), CryIA(c), and CryIB toxins interact in vitro with the epithelial microvilli of Malpighian tubules. In addition, CryIA(c) toxin also adheres to the basement membrane of the midgut epithelium.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
82 articles.
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