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Catalytic Site Atlas Search Results
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Catalytic Site Atlas

CSA LITERATURE entry for 1h4g

E.C. nameendo-1,4-beta-xylanase
SpeciesBacillus agaradhaerens (Bacillus agaradherans)
E.C. Number (IntEnz) 3.2.1.8
CSA Homologues of 1h4g
CSA Entries With UniProtID
CSA Entries With EC Number 3.2.1.8
PDBe Entry 1h4g
PDBSum Entry 1h4g
MACiE Entry 1h4g

Literature Report

IntroductionEndoxylanases 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.
MechansimThe 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.
Reaction

Catalytic Sites for 1h4g

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
GluA184184macie:sideChainInitially used as a general acid protonating the leaving residue, later used as a general base to activate the catalytic water molecule.
GluA9494macie:sideChainNucleophilic attack of C1 forming the glycosyl-enzyme intermediate.

Annotated By Reference To The Literature - Site 2 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
GluB184184macie:sideChainInitially used as a general acid protonating the leaving residue, later used as a general base to activate the catalytic water molecule.
GluB9494macie:sideChainNucleophilic attack of C1 forming the glycosyl-enzyme intermediate.

Literature References

Notes:
Sabini E
Catalysis and specificity in enzymatic glycoside hydrolysis: a 2,5B conformation for the glycosyl-enzyme intermediate revealed by the structure of the Bacillus agaradhaerens family 11 xylanase.
Chem Biol 1999 6 483-492
PubMed: 10381409
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