Abstract
Background: The enzymatic hydrolysis of glycosides involves the formation and subsequent breakdown of a covalent glycosyl-enzyme intermediate via oxocarbenium-ion-like transition states. The covalent intermediate may be trapped on-enzyme using 2-fluoro-substituted glycosides, which provide details of the intermediate conformation and noncovalent interactions between enzyme and oligosaccharide. Xylanases are important in industrial applications - in the pulp and paper industry, pretreating wood with xylanases decreases the amount of chlorine-containing chemicals used. Xylanases are structurally similar to cellulases but differ in their specificity for xylose-based, versus glucose-based, substrates.
Results: The structure of the family 11 xylanase, Xyl11, from Bacillus agaradhaerens has been solved using X-ray crystallography in both native and xylobiosyl-enzyme intermediate forms at 1.78 Angstrom and 2.0 Angstrom resolution, respectively The covalent glycosyl-enzyme intermediate has been trapped using a 2-fluoro-2-deoxy substrate with a good leaving group. Unlike covalent intermediate structures for glycoside hydrolases from other families, the covalent glycosyl-enzyme intermediate in family 11 adopts an unusual B-2,B-5 conformation.
Conclusions: The 2,5B conformation found for the a-linked xylobiosyl-enzyme intermediate of Xyl11, unlike the C-4(1) chair conformation observed for other systems, is consistent with the stereochemical constraints required of the oxocarbenium-ion-like transition state. Comparison of the Xyl11 covalent glycosyl-enzyme intermediate with the equivalent structure for the related family 12 endoglucanase, CelB, from Streptomyces lividans reveals the likely determinants for substrate specificity in this dan of glycoside hydrolases.
| Original language | English |
|---|---|
| Pages (from-to) | 483-492 |
| Number of pages | 10 |
| Journal | Chemistry & Biology |
| Volume | 6 |
| Issue number | 7 |
| Publication status | Published - Jul 1999 |
Keywords
- boat conformation
- enzyme specificity
- transition state
- xylanase
- ACID-SEQUENCE SIMILARITIES
- X-RAY STRUCTURE
- ACTIVE-SITE
- MACROMOLECULAR STRUCTURES
- MOLECULAR REPLACEMENT
- ANGSTROM RESOLUTION
- FUSARIUM-OXYSPORUM
- CRYSTAL-STRUCTURES
- ENDOGLUCANASE-I
- LEAVING GROUP
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