Binding of Bacillus thuringiensis toxin Cry1Ac to multiple sites of cadherin in pink bollworm

Toxins from Bacillus thuringiensis (Bt) are widely used for pest control. In particular, Bt toxin CrylAc 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) (PBW). In conjunction with previous results showing that PBW 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 PBW. 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 CrylAc bound to recombinant BtR fragments, suggesting that CrylAc activation may occur either before or after receptor binding. (c) 2006 Elsevier Ltd. All rights reserved.