Synergism of Bacillus Thuringiensis Toxins by a Fragment of a Toxin-binding Cadherin.
From: Department of Entomology, University of Georgia, Athens, GA 30602-2603, USA.
Proceedings of the National Academy of Sciences of the United States of America
- Publish Date: Aug 2007
- ISSN: 0027-8424
- Volume: 104
- Issue: 35
- Pages: 13901-6
- Medium: Print
- Language: English
- Citation (JAMA): Chen Jiang, Hua Gang, Jurat-Fuentes Juan Luis, et al. Synergism of Bacillus Thuringiensis Toxins by a Fragment of a Toxin-binding Cadherin.. Proc. Natl. Acad. Sci. U.S.A. Aug 2007;104:13901-6
Abstract
The insecticidal crystal proteins produced by Bacillus thuringiensis (Bt) are broadly used to control insect pests with agricultural importance. The cadherin Bt-R(1) is a binding protein for Bt Cry1A toxins in midgut epithelia of tobacco hornworm (Manduca sexta). We previously identified the Bt-R(1) region most proximal to the cell membrane (CR12-MPED) as the essential binding region required for Cry1Ab-mediated cytotoxicity. Here, we report that a peptide containing this region expressed in Escherichia coli functions as a synergist of Cry1A toxicity against lepidopteran larvae. Far-UV circular dichroism and (1)H-NMR spectroscopy confirmed that our purified CR12-MPED peptide mainly consisted of beta-strands and random coils with unfolded structure. CR12-MPED peptide bound brush border membrane vesicles with high affinity (K(d) = 32 nM) and insect midgut microvilli but did not alter Cry1Ab or Cry1Ac binding localization in the midgut. By BIAcore analysis we demonstrate that Cry1Ab binds CR12-MPED at high (9 nM)- and low (1 microM)-affinity sites. CR12-MPED-mediated Cry1A toxicity enhancement was significantly reduced when the high-affinity Cry1A-binding epitope ((1416)GVLTLNIQ(1423)) within the peptide was altered. Because the mixtures of low Bt toxin dose and CR12-MPED peptide effectively control target insect pests, our discovery has important implications related to the use of this peptide to enhance insecticidal activity of Bt toxin-based biopesticides and transgenic Bt crops.
Mesh Headings (Keywords): Animals, Bacterial Proteins, Bacterial Toxins, Endotoxins, Escherichia coli, Hemolysin Proteins, Kinetics, Larva, Manduca, Peptide Fragments, Protein Denaturation, Protein Folding, Recombinant Proteins
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