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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 2his

E.C. nameendo-1,4-beta-xylanase
SpeciesCellulomonas fimi ()
E.C. Number (IntEnz) 3.2.1.8
CSA Homologues of 2hisThere are 144 Homologs
CSA Entries With UniProtID P07986
CSA Entries With EC Number 3.2.1.8
PDBe Entry 2his
PDBSum Entry 2his
MACiE Entry 2his

Literature Report

Introductionbeta-1,4-glycanase Cex from Cellulomonas fimi belongs to glucoside hydrolases family 10. It hydrolyses xylan and, to a lesser extent, carboxymethylcellulose and also a range of soluble aryl xylosides, xylobiosides, glucosides and cellobiosides. It hydrolyses the beta-glycosidic bond with retention of the anomeric configuration, i.e. it is a retaining glycosidase.
MechansimRetaining glycosidases uses a double-displacement mechanism in which a covalent glycosyl-enzyme intermediate is formed and hydrolysed in a general acid/base catalysed process through oxocarbenium ion-like transition states, or possibly through oxocarbenium ion intermediates. Cex uses Glu233 as a nucleophile to attack the anomeric carbon in forming the covalent enzyme-substrate intermediate whilst Glu127 acts as the general acid/base to protonate the glycosidic oxygen and activate a water molecule to hydrolyse the enzyme-substrate complex. Transition state stabilisation is achieved by a low barrier hydrogen bond between the sugar C2 hydroxyl group and the carbonyl carbon of the Glu233 carboxylate group.
Reaction

Catalytic Sites for 2his

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AlaA127168macie:sideChainIt protonates the oxygen atom of the glycosidic bond. It deprotonates and activates a water molecule to allow it to hydrolyse the covalent enzyme-substrate intermediate.

Literature References

Notes:Two EC codes, 3.2.1.8 and 3.2.1.91 are given to the enzyme as it has a range of substrates of which the major ones are xylan and cellulose. The numbering of the glutamate residue may be different in different papers. When the signal sequence is included in numbering, Glu233 and Glu127 are referred to as Glu274 and Glu168 respectively.
Tull D
Glutamic acid 274 is the nucleophile in the active site of a "retaining" exoglucanase from Cellulomonas fimi.
J Biol Chem 1991 266 15621-15625
PubMed: 1678739
Notenboom V
Insights into transition state stabilization of the beta-1,4-glycosidase Cex by covalent intermediate accumulation in active site mutants.
Nat Struct Biol 1998 5 812-818
PubMed: 9731776
MacLeod AM
The acid/base catalyst in the exoglucanase/xylanase from Cellulomonas fimi is glutamic acid 127: evidence from detailed kinetic studies of mutants.
Biochemistry 1994 33 6371-6376
PubMed: 7910761
Hubbard CA
Reversal of reserpine-induced catalepsy by selective D1 and D2 dopamine agonists.
Mov Disord 1993 8 473-478
PubMed: 7901761
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