Binding and Synergizing Motif within Coleopteran Cadherin Enhances Cry3Bb Toxicity on the Colorado Potato Beetle and the Lesser Mealworm

Cry3Bb toxin from <i>Bacillus thuringiensis</i> is an important insecticidal protein due to its potency against coleopteran pests, especially rootworms. Cadherin, a protein in the insect midgut epithelium, is a receptor of Cry toxins; in some insect species toxin-binding domains of cadherins-synergized Cry toxicity. Previously, we reported that the DvCad1-CR8-10 fragment of <i>Diabrotica virgifera virgifera</i> cadherin-like protein (GenBank Accession #EF531715) enhanced Cry3Bb toxicity to the Colorado Potato Beetle (CPB), <i>Leptinotarsa</i> <i>decimlineata</i> (<i>L. decimlineata</i>). We report that individual CR domains of the DvCad1-CR8-10 fragment were found to have strong binding affinities to &#945;-chymotrypsin-treated Cry3Bb. The dissociation constant (<i>K_d</i>) of Cry3Bb binding to the CR8, CR9, and CR10 domain was 4.9 nM, 28.2 nM, and 4.6 nM, respectively. CR8 and CR10, but not CR9, enhanced Cry3Bb toxicity against <i>L. decimlineata</i> and the lesser mealworm <i>Alphitobius diaperinus</i> neonates. In-frame deletions of the DvCad1-CR10 open reading frame defined a high-affinity binding and synergistic site to a motif in residues I1226&#8722;D1278. A 26 amino acid peptide from the high affinity Cry3Bb-binding region of CR10 functioned as a Cry3Bb synergist against coleopteran larvae.

Abstract licence: CC BY

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