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CSA entry for 1js4
Original Entry
Title:
Glycosyl hydrolase
Compound:
Endo-exocellulase e4
Mutant:
No
UniProt/Swiss-Prot:
P26221-GUN4_THEFU
EC Class:
3.2.1.4
Other CSA Entries:
Overview of all sites for 1js4
Homologues of 1js4
Entries for UniProt/Swiss-Prot: P26221
Entries for EC: 3.2.1.4
Other Databases:
PDB entry: 1js4
PDBsum entry: 1js4
UniProt/Swiss-Prot: P26221
IntEnz entry: 3.2.1.4
Literature Report:
Introduction:
Cellulase E4 from Thermomonospora is both exo- and endo- cellulases, catalysing the hydrolysis of cellulose. It contains both a family 9 catalytic domain, exhibiting an (alpha/apha)6 barrel fold and a family III cellulose binding domain, having an antiparallel beta-sandwich fold.
Mechanism:
Same as the other members of family 9 cellulase, E4 endo/exocellulase cleaves cullulose with inversion of configuration at the anomeric carbon. In the mechanism, an acid protonates the glycosidic oxygen and a base extracts a nucleophilic water that attacks the anomeric carbon. Here, Glu424 is the acid. Both Asp 58 and Asp 55 hydrogen bond to the attacking water and both of them appear to contribute to the activation of the water molecule. Asp58 appears better oriented to accept a proton from the water than Asp55.
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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
ASPA 55 101Sidechain
ElectrostaticWater
It forms a hydrogen bond to the water molecule, which nucleophillically attacks the glycosidic bond of the substrate in hydrolysis, to activate it.
Evidence from paper Evidence concerns Evidence type
PubMed ID 9334746 Current protein Structural similarity to homologue of known mechanism
PubMed ID 9334746 Current protein Residue is positioned appropriately (ligand position known)

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
ASPA 58 104Sidechain
Acid/baseWater
It deprotonates the water molecule, which nucleophillically attacks the glycosidic bond of the substrate in hydrolysis.
Evidence from paper Evidence concerns Evidence type
PubMed ID 9334746 Current protein Structural similarity to homologue of known mechanism
PubMed ID 9334746 Current protein Residue is positioned appropriately (ligand position known)

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
GLUA 424 470Sidechain
Acid/baseSubstrate
It acts as an acid to protonate the glycosidic oxygen.
Evidence from paper Evidence concerns Evidence type
PubMed ID 9334746 Current protein Structural similarity to homologue of known mechanism
PubMed ID 9334746 Current protein Residue is positioned appropriately (ligand position known)
References:
1
Structure and mechanism of endo/exocellulase E4 from Thermomonospora fusca.
J. Sakon and D. Irwin and D. B. Wilson and P. A. Karplus
Nat Struct Biol 4, (10) 810-8, (1997).
9334746
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