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KMID : 0380220070400010058
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Journal of Biochemistry and Molecular Biology
2007 Volume.40 No. 1 p.58 ~ p.64
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High Level of Soluble Expression in Escherichia coli and Characterisation of the Cloned Bacillus thuringiensis Cry4Ba Domain III Fragment
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Chayaratanasin Poramed
Moonsom Seangdeun
Sakdee Somsri
Chaisri Urai
Katzenmeier Gerd
Angsuthanasombat Chanan
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Abstract
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Similar to the other known structures of Bacillus thuringiensis Cry δ-endotoxins, the crystal structure of the 65-kDa activated Cry4Ba toxin comprises three domains which are, from the N- to C-terminus, a bundle of α-helices, a three-β-sheet domain, and a β-sandwich. To investigate the properties of the C-terminal domain III in isolation from the rest of the toxin, the cloned Cry4Ba-domain III was over-expressed as a 21-kDa soluble protein in Escherichia coli, which cross-reacted with anti-Cry4Ba domain III monoclonal antibody. A highly-purified domain III was obtained in a monomeric form by ion-exchange and size-exclusion FPLC. Circular dichroism spectroscopy indicated that the isolated domain III fragment distinctly exists as a β-sheet structure, corresponding to the domain III structure embodied in the Cry4Ba crystal structure. In vitro binding analysis via immuno-histochemical assay revealed that the Cry4Ba-domain III protein was able to bind to the apical microvilli of the susceptible Stegomyia aegypti larval midguts, albeit at lower-binding activity when compared with the full-length active toxin. These results demonstrate for the first time that the C-terminal domain III of the Cry4Ba mosquito-larvicidal protein, which can be isolated as a native folded monomer, conceivably participates in toxin-receptor recognition.
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KEYWORD
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Bacillus thuringiensis, Cry4Ba δ-endotoxin, Immunohistochemical assay, Stegomyia aegypti, β-sheet structure
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