Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2006
Publication Date: 2/1/2007
Citation: Fabrick, J.A., Tabashnik, B.E. (2007). Binding of Bacillus thuringiensis toxin CrylAc to multiple sites of cadherin in pink bollworm. Insect Biochemistry and Molecular Biology, 37:97-106
Interpretive Summary: Protein toxins from the bacterium Bacillus thuringiensis (Bt) kill key agricultural insect pests and have been genetically engineered into crops. Cry lAc is a toxin produced in Bt cotton and is effective for controlling the pink bollworm, a major insect pest of cotton. Here we show that a pink bollworm cadherin protein binds to CrylAc. We produced nine different proteins corresponding to different regions within the cadherin and assayed for specific CrylAc-binding sites. At least two toxin binding regions were found and each was located in the extracellular portion of the protein and adjacent to the membrane spanning domain. In conjunction with previous results showing that pink bollworm resistance to CrylAc is linked with mutations in the cadherin gene, the results reported here support the hypothesis that cadherin is a receptor for CrylAc in pink bollworm. In addition, the pink bollworm cadherin binds to both activated and protoxin forms of Cry 1 Ac, suggesting that the mode of action of Bt toxin is complex.
Technical Abstract: Toxins from Bacillus thuringiensis (Bt) are widely used for pest control. In particular, Bt toxin Cry lAc produced by transgenic cotton kills some key lepidopteran pests. We found that CrylAc binds to recombinant peptides corresponding to extracellular regions of a cadherin protein (BtR) in a major cotton pest, pink bollworm (Pectinophora gossypiella). In conjunction with previous results showing that pink bollworm resistance to CrylAc is linked with mutations in the BtR gene, the results reported here support the hypothesis that BtR is a receptor for CrylAc in pink bollworm. Similar to other lepidopteran cadherins that bind Bt toxins, BtR has at least two CrylAc-binding domains in cadherin-repeat regions 10 and 11, which are immediately adjacent to the membrane proximal region. However, unlike cadherins from Manduca sexta and Bombyx mori, toxin binding was not seen in regions more distal from the membrane proximal region. We also found that both the protoxin and activated toxin forms of Cry lAc bound to recombinant BtR fragments, suggesting that CrylAc activation may occur either before or after receptor binding.