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Analysis of non-active engineered Bacillus thuringiensis crystal proteins
D Bosch1, B Visser, W J Stiekema
1Department of Molecular Biology, Centre for Plant Breeding and Reproduction Research (CPRO-DLO), Wageningen, The Netherlands.
FEMS Microbiology Letters
|May 1, 1994
Summary
Engineering Bacillus thuringiensis crystal proteins (Cry proteins) for insecticidal specificity is challenging. Modifying domain II loops of CryIA(b) with CryIE sequences resulted in inactive, insoluble proteins, indicating difficulties in protein refolding and potential structural differences.
Area of Science:
- Molecular biology
- Insect toxicology
- Protein engineering
Background:
- Bacillus thuringiensis crystal (Cry) proteins exhibit insecticidal specificity.
- Specificity is mediated by Cry protein interactions with insect midgut binding sites.
- Domain II of Cry proteins is crucial for determining binding specificity.
Purpose of the Study:
- To identify specific sequences within domain II of CryIA(b) responsible for insecticidal binding.
- To investigate the impact of domain II loop swapping between CryIA(b) and CryIE on protein function and specificity.
Main Methods:
- Site-directed mutagenesis: Loops in domain II of CryIA(b) were replaced with corresponding regions from CryIE.
- Expression and purification: Mutant and wild-type genes were expressed in Escherichia coli.
- In vitro refolding and activity assays: Solubilized aggregates were tested for proper refolding and biological activity.
Main Results:
- Expression of engineered CryIA(b) resulted in insoluble, inactive protein aggregates.
- Mutant proteins failed to refold correctly after in vitro solubilization with urea.
- Mutant proteins exhibited increased protease sensitivity and lacked insecticidal activity compared to wild-type CryIA(b).
Conclusions:
- Engineering CryI proteins by domain swapping is difficult due to issues with protein folding and solubility.
- The conformation of domain II may differ significantly between CryI and CryIIIA proteins, hindering successful engineering efforts.
- Further research is needed to understand structural constraints for successful Cry protein engineering.