Cry1Ac Protoxin and Its Activated Toxin from Bacillus thuringiensis Act Differentially during the Pathogenic Process

Area of Science:

• Molecular Biology
• Insect Toxicology
• Biochemistry

Background:

• The dual model of Bacillus thuringiensis (Bt) insecticidal mechanism suggests both Cry1A protoxin and activated toxin kill insects.
• However, molecular-level differences in toxic pathways between protoxin and activated toxin remain unclear.

Purpose of the Study:

• To investigate the molecular differences in toxicity pathways between Cry1Ac protoxin and activated toxin.
• To elucidate the binding sites and endocytosis pathways of Cry1Ac protoxin and activated toxin.

Main Methods:

• Utilized the CF-203 cell line derived from the midgut of Choristoneura fumiferana.
• Analyzed Cry1Ac protoxin presence and binding sites in the midgut of Plutella xylostella.

Main Results:

• Identified distinct binding sites and endocytosis pathways for Cry1Ac protoxin and activated toxin in CF-203 cells.
• Observed predominant Cry1Ac protoxin in Plutella xylostella midgut early after ingestion, causing epithelial damage.
• Demonstrated different binding sites on brush border membrane vesicles for protoxin compared to the activated toxin.

Conclusions:

• Findings support the dual mode of action for Bacillus thuringiensis Cry1A proteins.
• Improved understanding of the molecular features contributing to Cry1Ac protoxin toxicity.