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Identification of Bacillus thuringiensis Cry3Aa toxin domain II loop 1 as the binding site of Tenebrio molitor

Fernando Zúñiga-Navarrete1, Isabel Gómez1, Guadalupe Peña2

  • 1Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. postal 510-3, Cuernavaca 62250, Morelos, Mexico.

Insect Biochemistry and Molecular Biology
|February 21, 2015
PubMed

Insights

Bacillus thuringiensis Cry3Aa toxin binds to Tenebrio molitor cadherin CR12 via its domain II loop 1. This interaction is crucial for toxin binding and toxicity, as confirmed by antibody competition and mutant analysis.

Area of Science:

  • Insect toxicology
  • Molecular biology
  • Protein-protein interactions

Background:

  • Bacillus thuringiensis Cry toxins are insecticidal proteins that function by binding to specific larval midgut proteins.
  • This binding initiates toxin oligomerization, membrane insertion, and pore formation, leading to cell lysis and insect death.
  • Domain II loop regions of Cry toxins are implicated in receptor binding, with insect cadherins playing a key role in facilitating toxin binding and oligomerization.

Purpose of the Study:

  • To identify the specific binding site of Bacillus thuringiensis Cry3Aa toxin on Tenebrio molitor brush border membranes.
  • To elucidate the role of Cry3Aa domain II loop 1 in the interaction with T. molitor cadherin.

Main Methods:

  • Isolation of a VHH antibody (VHHA5) using phage display that specifically binds to Cry3Aa loop 1.
  • Competition assays to assess the binding of VHHA5 and Cry3Aa to T. molitor brush border membranes and cadherin fragments.
  • Analysis of a Cry3Aa loop 1 mutant for binding affinity to T. molitor cadherin CR12 and VHHA5.

Main Results:

  • VHHA5 antibody binds to Cry3Aa loop 1 and competes with Cry3Aa binding to T. molitor brush border membranes.
  • VHHA5 also competes with Cry3Aa binding to the T. molitor cadherin fragment CR12, indicating domain II loop 1 is involved in this interaction.
  • A Cry3Aa loop 1 mutant with enhanced toxicity showed increased binding affinity to both T. molitor CR12 and VHHA5.

Conclusions:

  • Cry3Aa domain II loop 1 is a critical binding site for the T. molitor cadherin CR12.
  • This interaction is essential for Cry3Aa toxin binding and subsequent toxicity in Tenebrio molitor.
Keywords:
Bacillus thuringiensisCry3Aa toxinPhage displayReceptor bindingTenebrio molitorVHH antibodies

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