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Mutations at calcium binding site III in cyclodextrin glycosyltransferase improve β-cyclodextrin specificity
Xiaofeng Ban1, Zhengbiao Gu2, Caiming Li1
1School of Food Science and Technology, Jiangnan University, Wuxi 214122, China.
Modifying a specific site on cyclodextrin glycosyltransferases (CGTases) with charged amino acids significantly enhances beta-cyclodextrin production. These engineered CGTases show improved specificity and are more suitable for industrial applications.
Area of Science:
- Enzymology
- Biotechnology
- Protein Engineering
Background:
- Cyclodextrin glycosyltransferases (CGTases) are crucial industrial enzymes for producing cyclodextrins from starch.
- Calcium binding site III (CaIII) is known to influence CGTase activity and specificity.
Purpose of the Study:
- To investigate the impact of amino acid substitutions at position 315 within CaIII on the product specificity of Bacillus circulans STB01 CGTase.
- To identify CGTase variants with enhanced beta-cyclodextrin production capabilities for industrial applications.
Main Methods:
- Site-directed mutagenesis was employed to replace Ala315 with arginine, aspartic acid, threonine, leucine, and valine.
- The wild-type and mutant cgt genes were expressed in Bacillus subtilis WB600.
- Enzyme activity and product specificity were analyzed, with a focus on beta-cyclodextrin production under industrially relevant conditions.
Main Results:
- Amino acid substitutions at position 315 in CaIII significantly affect CGTase product specificity.
- Replacement of Ala315 with charged residues (arginine and aspartic acid) notably enhanced beta-cyclodextrin specificity.
- Mutants A315R and A315D exhibited approximately 10% higher beta-cyclodextrin activity and superior production yields compared to the wild-type enzyme.
Conclusions:
- The CaIII site plays a critical role in determining the cyclodextrin product specificity of CGTases.
- Charged amino acid substitutions at position 315 can stabilize CaIII, leading to enhanced beta-cyclodextrin production.
- The A315R and A315D mutants demonstrate significant potential for industrial-scale beta-cyclodextrin manufacturing.
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