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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1exp

E.C. nameendo-1,4-beta-xylanase
SpeciesCellulomonas fimi ()
E.C. Number (IntEnz) 3.2.1.8
CSA Homologues of 1expThere are 80 Homologs
CSA Entries With UniProtID P07986
CSA Entries With EC Number 3.2.1.8
PDBe Entry 1exp
PDBSum Entry 1exp
MACiE Entry 1exp

Literature Report

IntroductionThe Glycosyl hydrolases form a ubiquitous group of enzymes involved in carbohydrate metabolism. The class can be sub divided according to the stereoselective reaction outcomes, with hydrolysis occurring with net retention or inversion of the anomeric configuration. The protein in question catalyses the hydrolysis with retention. The enzyme has been reported to preferentially cleave a cellobiose unit rather than glucose from the non-reducing end of cellulose, and has been identified as biotechnologically important because of its reaction specificity between xylan and cellulose. The existence of multiple hydrolysis substrate results in more than one EC code for the same active site.
MechansimThe nucleophilic Glu 233 acts in concert with the general acid/base Glu 127 to form the glycosyl-enzyme intermediate, as implicated by trapped intermediate crystal structures. De-glycolisation occurs by nucleophilic attack of a water molecule at the anomeric carbon, resulting in a second inversion (and net retention of configuration). The de-glycosylated carbohydrate then leaves the active site, freeing the enzyme for further catalysis.
Reaction

Catalytic Sites for 1exp

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
GluA233274macie:sideChainThe residue acts as a nucleophile towards the substrate glycosidic bond, forming an enzyme-substrate intermediate. Interactions though hydrogen bonds with surrounding residues (Asn 169 and His 205) influences the residue's nucleophilicity.
GluA127168macie:sideChainThe residue acts as a general acid towards the breaking glycosidic bond in concert with nucleophilic attack by Glu 233. The residue then acts as a general base towards the hydrolytic water molecule which attacks the enzyme-substrate intermediate.
AsnA169210macie:sideChainThe residue hydrogen bonds to the catalytic Gln 233 residue, activating it for nucleophilic attack at the substrate.
HisA205246macie:sideChainThe residue hydrogen bonds to the catalytic Gln 233, activating it towards nucleophilic attack at the substrate.
AspA235276macie:sideChainThe residue's imidazole ring is correctly orientated to hydrogen bond to His 205. This interaction is thought to assist the hydrolysis of the glycosyl-enzyme intermediate by stabilising the released carboxylate residue.

Literature References

Notes:
White A
Crystallographic observation of a covalent catalytic intermediate in a beta-glycosidase.
Nat Struct Biol 1996 3 149-154
PubMed: 8564541
Suzuki R
Crystallographic snapshots of an entire reaction cycle for a retaining xylanase from Streptomyces olivaceoviridis E-86.
J Biochem 2009 146 61-70
PubMed: 19279191
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