Synergism of Bacillus thuringiensis toxins by a fragment of a toxin-binding cadherin.
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.
Chen
Jiang
J
Department of Entomology, University of Georgia, Athens, GA 30602-2603, USA.
Hua
Gang
G
Jurat-Fuentes
Juan Luis
JL
Abdullah
Mohd Amir
MA
Adang
Michael J
MJ
D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004731:Endotoxins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004926:Escherichia coli / Q000235:genetics; D006460:Hemolysin Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D007814:Larva / Q000187:drug effects; D018402:Manduca / Q000187:drug effects / Q000254:growth & development; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D011489:Protein Denaturation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis