Univalent Binding of the Cry1Ab Toxin of Bacillus thuringiensis to a Conserved Structural Motif in the Cadherin Receptor BT-R1

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• 作者：Natalya B. Griko ; Laura Rose-Young ; Xuebin Zhang ; Lindy Carpenter ; Mehmet Candas ; Mohamed A. Ibrahim ; Matthew Junker ; Lee A. Bulla ; Jr.
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：September 4, 2007
• 年：2007
• 卷：46
• 期：35
• 页码：10001 - 10007
• 全文大小：550K
• 年卷期：v.46,no.35(September 4, 2007)
• ISSN：1520-4995

文摘

The Cry1Ab toxin produced by Bacillus thuringiensis (Bt) exerts insecticidal action uponbinding to BT-R₁, a cadherin receptor localized in the midgut epithelium of the tobacco hornworm Manducasexta [Dorsch, J. A., Candas, M., Griko, N. B., Maaty, W. S., Midboe, E. G., Vadlamudi, R. K., andBulla, L. A., Jr. (2002) Cry1A toxins of Bacillus thuringiensis bind specifically to a region adjacent tothe membrane-proximal extracellular domain of BT-R₁ in Manduca sexta: involvement of a cadherin inthe entomopathogenicity of Bacillus thuringiensis, Insect Biochem. Mol. Biol. 32, 1025-1036]. BT-R₁represents a family of invertebrate cadherins whose ectodomains (ECs) are composed of multiple cadherinrepeats (EC1 through EC12). In the present work, we determined the Cry1Ab toxin binding site in BT-R₁in the context of cadherin structural determinants. Our studies revealed a conserved structural motif fortoxin binding that includes two distinct regions within the N- and C-termini of EC12. These regions arecharacterized by unique sequence signatures that mark the toxin-binding function in BT-R₁ as well as inhomologous lepidopteran cadherins. Structure modeling of EC12 discloses the conserved motif as a singlebroad interface that holds the N- and C-termini in close proximity. Binding of toxin to BT-R₁, which isunivalent, and the subsequent downstream molecular events responsible for cell death depend on theconserved motif in EC12.