Residue 544 in Domain III of the Bacillus thuringiensis Cry1Ac Toxin is Involved in Protein Structure Stability
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A unique residue W544 in the β18–β19 loop of the Bacillus thuringiensis Cry1Ac toxin has been implicated in its toxicity. In this study, the effects of mutations at this residue on protein stability during protease treatment, UV irradiation, and preservation were examined. Residue 544 of Cry1Ac was involved in maintaining structural stability, and substitution of a polar group at this position was unfavorable to protein stability. One mutant, W544F, produced larger crystals and was more stable. This mutant showed greater resistance to UV radiation than the wild type Cry1Ac but retained equal toxicity. This is the first report showing that residue 544 in the Cry1Ac domain III plays a significant role in toxin structural stability. Our W544F mutant is a significant development in terms of field applications of Cry1Ac toxin.
KeywordsBacillus thuringiensis Stability Proteolysis UV irradiation Tryptophan
Insecticidal crystal protein
Sodium dodecyl sulfate polyacrylamide gel electrophoresis
Atomic force microscope
We thank Mr. Shan Shiping for technical assistance of AFM. This work was supported in part by 863 grants (2008AA100801, 2006AA02Z187, 2006AA10212) and a grant from the Ph.D. Programs Foundation of Ministry of Education of China (20060452006).
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