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A Cry1Ac toxin variant generated by directed evolution has enhanced toxicity against Lepidopteran insects
Shiping Shan1, Youming Zhang, Xuezhi Ding
1Key Laboratory of Microbial Molecular Biology of Hunan Province, College of Life Science, Hunan Normal University, Changsha, 410081, People's Republic of China.
Current Microbiology
|July 30, 2010
Summary
Bacillus thuringiensis (Bt) Cry1Ac toxin variants were engineered for enhanced insecticidal activity. A single mutation (T524N) improved efficacy against Spodoptera exigua larvae, offering new insights into Bt toxin-receptor interactions.
Area of Science:
- Biochemistry
- Molecular Biology
- Entomology
Background:
- Bacillus thuringiensis (Bt) Cry1Ac insecticidal crystal proteins are vital biological control agents for lepidopteran pests.
- Understanding the structure-function relationship of Bt toxins is crucial for developing more effective pest control strategies.
Purpose of the Study:
- To engineer a Cry1Ac toxin variant with enhanced insecticidal activity using protein engineering techniques.
- To investigate the impact of specific mutations on the insecticidal properties and crystal formation of Cry1Ac toxin.
- To elucidate the role of domain III in the insecticidal activity and receptor interactions of Cry1Ac toxin.
Main Methods:
- Utilized error-prone PCR, StEP shuffling, and Red/ET homologous recombination to modify the cry1Ac toxin gene.
- Screened toxin variants through insect bioassays against Spodoptera exigua and Helicoverpa armigera larvae.
- Analyzed mutant and original Cry1Ac proteins using theoretical molecular modeling and observed crystal formation in an acrystalliferous strain.
Main Results:
- A Cry1Ac toxin variant, T524N, exhibited increased insecticidal activity against Spodoptera exigua larvae while retaining activity against Helicoverpa armigera.
- The T524N mutation resulted in a single amino acid substitution at position 524, located in domain III.
- Mutant T524N formed more, smaller bipyramidal crystals and displayed a more hydrophobic surface in domain III, suggesting altered receptor interactions.
Conclusions:
- A single amino acid substitution (T524N) in Cry1Ac toxin significantly enhances insecticidal activity against specific lepidopteran pests.
- Domain III of Cry1Ac toxin plays a critical role in insecticidal activity, with mutations influencing hydrophobic interactions with target receptors.
- This study provides valuable biological evidence for the structural function of domain III, advancing the understanding of Bt toxin-receptor macromolecule interactions.
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