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Structural elements in dextran glucosidase responsible for high specificity to long chain substrate
Wataru Saburi1, Haruhide Mori, Saori Saito
1Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Biochimica Et Biophysica Acta
|March 1, 2006
Summary
Streptococcus mutans dextran glucosidase (SMDG) exhibits higher activity on long isomaltooligosaccharides than Bacillus oligo-1,6-glucosidase. Key structural elements, Trp238 and a short loop, enhance SMDG
Area of Science:
- Enzymology
- Structural Biology
- Microbiology
Background:
- Dextran glucosidase from Streptococcus mutans (SMDG) and Bacillus oligo-1,6-glucosidases are glycoside hydrolase family 13 enzymes.
- Both enzymes specifically cleave alpha-1,6-glucosidic linkages at the non-reducing end of substrates to release glucose.
Purpose of the Study:
- To identify structural elements responsible for the high activity of SMDG toward long isomaltooligosaccharides.
- To compare the structure-function relationship between SMDG and Bacillus cereus oligo-1,6-glucosidase.
Main Methods:
- Conformational comparison between SMDG and a known 3D structure of B. cereus oligo-1,6-glucosidase.
- Site-directed mutagenesis (W238A) and creation of chimeric enzymes.
Main Results:
- Trp238 and a short beta-->alpha loop 4 in SMDG are crucial for high activity on long substrates.
- W238A mutation decreased the affinity for the subsite +2.
- Mutants and chimeric enzymes showed reduced preference for longer substrates.
Conclusions:
- Trp238 and the short beta-->alpha loop 4 are essential structural determinants for SMDG's high activity on long isomaltooligosaccharides.
- These findings provide insights into the substrate specificity of glycoside hydrolase family 13 enzymes.
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