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KMID : 0624620140470100546
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BMB Reports
2014 Volume.47 No. 10 p.546 ~ p.551
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Functional characterizations of residues Arg-158 and Tyr-170 of the mosquito-larvicidal Bacillus thuringiensis Cry4Ba
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Leetachewa Somphob
Moonsom Saengduen
Chaisri Urai
Khomkhum Narumol
Yoonim Nonglak
Wang Ping
Angsuthanasombat Chanan
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Abstract
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The insecticidal activity of Bacillus thuringiensis (Bt) Cry toxins involves toxin stabilization, oligomerization, passage across the peritrophic membrane (PM), binding to midgut receptors and pore-formation. The residues Arg-158 and Tyr-170 have been shown to be crucial for the toxicity of Bt Cry4Ba. We characterized the biological function of these residues. In mosquito larvae, the mutants R158A/E/Q (R158) could hardly penetrate the PM due to a significantly reduced ability to alter PM permeability; the mutant Y170A, however, could pass through the PM, but degraded in the space between the PM and the midgut epithelium. Further characterization by oligomerization demonstrated that Arg-158 mutants failed to form correctly sized high-molecular weight oligomers. This is the first report that Arg-158 plays a role in the formation of Cry4Ba oligomers, which are essential for toxin passage across the PM. Tyr-170, meanwhile, is involved in toxin stabilization in the toxic mechanism of Cry4Ba in mosquito larvae.
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KEYWORD
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Aedes aegypti, Bacillus thuringiensis, Cry4Ba toxin, Larvicidal activity, Peritrophic membrane
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