Get   for     ? 
 Site search     ? 
Catalytic Site Atlas Version 2.2.12
Find Annotated Site: PDB code:
Swiss-Prot code:
EC number:
Help
CSA entry for 1h4g
Original Entry
Title:
Glycoside hydrolase
Compound:
Xylanase
Mutant:
No
UniProt/Swiss-Prot:
Q7SIE3-Q7SIE3
EC Class:
3.2.1.8
Other CSA Entries:
Overview of all sites for 1h4g
Homologues of 1h4g
Entries for UniProt/Swiss-Prot: Q7SIE3
Entries for EC: 3.2.1.8
Other Databases:
PDB entry: 1h4g
PDBsum entry: 1h4g
UniProt/Swiss-Prot: Q7SIE3
IntEnz entry: 3.2.1.8
Literature Report:
Introduction:
Endoxylanases are found in five of the 71 glycoside hydrolase families (5, 10, 11, 43 and 54). Xylanase is a member of family 11 and performs hydrolysis using acid-base catalysis with cleavage of the beta-1,4 bonds with retention of anomeric configuration. The enzymatic hydrolysis of hemicellulose is of major importance in the pulp and paper industry: xylanase pretreatment in the bleaching process is effective in reducing the amount of environmentally toxic chlorine and chlorine-containing chemicals used.

Mechanism:
The hydrolysis of the glycosidic bond occurs through a double displacement mechanism. First, a covalent glycosyl-enzyme intermediate is formed by the nucleophilic attack of the Glu94 side chain on the C1 position of the substrate. Second, the covalent glycosyl-enzyme intermediate is hydrolysed and the xylose is released.

As the covalent intermediate is formed the xylose residue which is attacked by the nucleophile (Glu94) addopts a 2S5 boat conformation. This fulfils the stereochemical requirements for the oxocarbenium ion- like transition state of the retaining mechanism. Water is activated by the general base Glu184 and positioned for a classic in line nucleophilic attack of C1.
Sites:

Click to Display Catalytic Site (Get help with this section)
Found by:
Literature reference 
PsiBLAST alignment on 1bvv

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
GLUA 94 94Sidechain
NucleophileSubstrate
Nucleophilic attack of C1 forming the glycosyl-enzyme intermediate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 12559743 Current protein Kinetic studies
PubMed ID 12559743 Current protein pH dependence of reaction
PubMed ID 10381409 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 12559743 Current protein Mutagenesis of residue
PubMed ID 11526340 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 11526340 Current protein Residue is covalently bound to intermediate, based on structural data
PubMed ID 10381409 Current protein Residue is covalently bound to intermediate, based on structural data

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
GLUA 184 184Sidechain
Acid/baseSubstrate
Acid/baseWater
Initially used as a general acid protonating the leaving residue, later used as a general base to activate the catalytic water molecule.
Evidence from paper Evidence concerns Evidence type
PubMed ID 12559743 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 12559743 Current protein pH dependence of reaction
PubMed ID 10381409 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 12559743 Current protein Kinetic studies
PubMed ID 11526340 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 10381409 Current protein Conservation of residue
Notes:

References:
Which EBI biological databases are available and how do I access them? EBI Site Map