The C-terminal protoxin region of Bacillus thuringiensis Cry1Ab toxin has a functional role in binding to GPI-anchored receptors in the insect midgut

Bacillus thuringiensis Cry toxins are used worldwide for controlling insects. Cry1Ab is produced as a 130-kDa protoxin that is activated by proteolytic removal of an inert 500 amino-acid-long C-terminal region, enabling the activated toxin to bind to insect midgut receptor proteins, leading to its m...

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Bibliographic Details
Published in:The Journal of biological chemistry 2018-12, Vol.293 (52), p.20263-20272
Main Authors: Peña-Cardeña, Arlen, Grande, Ricardo, Sánchez, Jorge, Tabashnik, Bruce E., Bravo, Alejandra, Soberón, Mario, Gómez, Isabel
Format: Article
Language:English
Subjects:
Animals
Bacillus thuringiensis
Bacillus thuringiensis Toxins
Bacterial Proteins - chemistry
Bacterial Proteins - metabolism
Endotoxins - chemistry
Endotoxins - metabolism
GPI-Linked Proteins - chemistry
GPI-Linked Proteins - metabolism
Hemolysin Proteins - chemistry
Hemolysin Proteins - metabolism
Insect Proteins - chemistry
Insect Proteins - metabolism
Intestinal Mucosa - metabolism
Larva - metabolism
Manduca - metabolism
Protein Structure and Folding
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Summary:Bacillus thuringiensis Cry toxins are used worldwide for controlling insects. Cry1Ab is produced as a 130-kDa protoxin that is activated by proteolytic removal of an inert 500 amino-acid-long C-terminal region, enabling the activated toxin to bind to insect midgut receptor proteins, leading to its membrane insertion and pore formation. It has been proposed that the C-terminal region is only involved in toxin crystallization, but its role in receptor binding is undefined. Here we show that the C-terminal region of Cry1Ab protoxin provides additional binding sites for alkaline phosphatase (ALP) and aminopeptidase N (APN) insect receptors. ELISA, ligand blot, surface plasmon resonance, and pulldown assays revealed that the Cry1Ab C-terminal region binds to both ALP and APN but not to cadherin. Thus, the C-terminal region provided a higher binding affinity of the protoxin to the gut membrane that correlated with higher toxicity of protoxin than activated toxin. Moreover, Cry1Ab domain II loop 2 or 3 mutations reduced binding of the protoxin to cadherin but not to ALP or APN, supporting the idea that protoxins have additional binding sites. These results imply that two different regions mediate the binding of Cry1Ab protoxin to membrane receptors, one located in domain II–III of the toxin and another in its C-terminal region, suggesting an active role of the C-terminal protoxin fragment in the mode of action of Cry toxins. These results suggest that future manipulations of the C-terminal protoxin region could alter the specificity and increase the toxicity of B. thuringiensis proteins.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.RA118.005101