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Catalytic Site Atlas Version 2.2.12
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CSA entry for 1itx
Original Entry
Title:
Hydrolase
Compound:
Glycosyl hydrolase
Mutant:
No
UniProt/Swiss-Prot:
P20533-CHI1_BACCI
EC Class:
3.2.1.14
Other CSA Entries:
Overview of all sites for 1itx
Homologues of 1itx
Entries for UniProt/Swiss-Prot: P20533
Entries for EC: 3.2.1.14
Other Databases:
PDB entry: 1itx
PDBsum entry: 1itx
UniProt/Swiss-Prot: P20533
IntEnz entry: 3.2.1.14
Literature Report:
Introduction:
Chitinase A1 from Bacillus circulans catalyses the hydrolysis of the 1,4-beta linkages of N-acetyl-D glucosamine polymers of chitin. For bacteria, this hydrolysis is utilised primarily as carbon and energy sources. Chitinase A1 is proposed to be very similar to hen egg-white lysozyme, differing only in that it undergoes a 'substrate assisted' mechanism.
Mechanism:
1. The nitrogen atom of the substrate pushes electrons up toward the acetyl group, causing the oxygen atom of the acetyl to nucleophilically attack the C1 atom of the substrate. This breaks the C1-O bond, and the leaving group oxygen atom is protonated by Glu 204.
2. Asp 200 stabilises the positive charge on the substrate.
3. Glu 204 then acts as a general base, deprotonating a water molecule and activating it for nucleophilic attack on the substrate C1 atom.
4. The N-acetyl group is reformed, and the product leaves.
Sites:

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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
ASPA 200 200Sidechain
ElectrostaticSubstrate
The side chain of Asp 200 stabilises the positively charged intermediate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 8103047 Current protein Mutagenesis of residue
PubMed ID 8103047 Current protein Structural similarity to homologue of known mechanism

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
GLUA 204 204Sidechain
Acid/baseSubstrate
Acid/baseWater
Glu 204 acts as a general acid/base by protonating the leaving group, and by deprotonating a water molecule to activate it.
Evidence from paper Evidence concerns Evidence type
PubMed ID 8103047 Current protein Structural similarity to homologue of known mechanism
Evidence from paper listed as having "No PubMed ID available." below. Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 8103047 Current protein Conservation of residue
Evidence from paper listed as having "No PubMed ID available." below. Current protein Structural similarity to homologue of known mechanism
PubMed ID 8103047 Current protein Mutagenesis of residue
Notes:

References:
1
Substrate-Assisted Catalysis Unifies Two Families of Chitinolytic Enzymes
Tews, I and Terwisscha van Scheltinga, A and Perrakis, K and Wilson, K and Dijkstra, B
J Am Chem Soc 119, 7954-7959 (1997)
No PubMed ID available
2
Identification of glutamic acid 204 and aspartic acid 200 in chitinase A1 of Bacillus circulans WL-12 as essential residues for chitinase activity.
T. Watanabe and K. Kobori and K. Miyashita and T. Fujii and H. Sakai and M. Uchida and H. Tanaka
J Biol Chem 268, (25) 18567-72, (1993).
8103047
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