Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2009
Publication Date: 7/3/2009
Citation: Fabrick, J.A., Oppert, C., Lorenzen, M.D., Oppert, B.S., Jurat-Fuentes, J.L. 2009. A Novel Tenebrio molitor Cadherin is a Functional Receptor for Bacillus thuringiensis Toxin Cry3Aa. Journal of Biological Chemistry. 284: 18401-18410 Interpretive Summary: Protein toxins from the bacterium Bacillus thuringiensis (Bt) kill key insect pests including those known to vector diseases and those found in agriculture. Although, the mode of action of Bt insecticidal toxins has been extensively studied in some insects, relatively little is known about the intoxication process of Cry toxins in Coleoptera (beetles). We evaluated whether a cadherin from the midgut of the Bt-sensitive coleopteran, Tenebrio molitor, is a functional receptor for Cry3Aa toxin. The T. molitor cadherin bound Cry3Aa toxin specifically, promoted Cry3Aa oligomerization, and conferred toxin susceptibility when expressed in cultured insect cells. These results support the hypothesis that T. molitor cadherin is a functional Cry3Aa receptor and suggest a common mode of action for Cry toxins in distinct insect orders. This information can be used to develop more coleopteran Bt toxins with increased toxicity and expanded host range.
Technical Abstract: Cry toxins produced by the bacterium Bacillus thuringiensis (Bt) are effective biological insecticides. Cadherin-like proteins have been reported as functional Cry1A toxin receptors in Lepidoptera. We present the first report demonstrating a functional interaction between the coleopteran-specific Cry3Aa toxin and a cadherin from a coleopteran insect. The Cry3Aa receptor cadherin was cloned from cDNA of midgut from Tenebrio molitor larvae, based on a partial cDNA sequence from a midgut expressed sequence tag database. The predicted protein sequence, TmCad1, has domain structure and a putative toxin binding region similar to those in lepidopteran cadherin Bt receptors. A TmCad1 peptide (rTmCad1p) containing the putative toxin binding region specifically interacted with Cry3Aa, demonstrated by dot blot and gel analysis assays. Results from oligomerization assays suggested that rTmCad1p promotes the formation of Cry3Aa toxin oligomers, and expression of rTmCad1p on the surface of cultured insect cells conferred susceptibility to Cry3Aa. These data demonstrate the functional role of TmCad1 as a Cry3Aa receptor in T. molitor and reveal similarities between the mode of action of Cry toxins in Lepidoptera and Coleoptera.