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Catalytic Site Atlas

CSA LITERATURE entry for 1ctn

E.C. namechitinase
SpeciesSerratia marcescens (Bacteria)
E.C. Number (IntEnz) 3.2.1.14
CSA Homologues of 1ctnThere are 67 Homologs
CSA Entries With UniProtID P07254
CSA Entries With EC Number 3.2.1.14
PDBe Entry 1ctn
PDBSum Entry 1ctn
MACiE Entry 1ctn

Literature Report

IntroductionThe chitinase enzymes catalyse the hydrolysis of chitin, a bio-polymer composed of 1,4 linked N-acetylglucosamine units, a major component of fungal cell walls and insect exoskeletons. The bacterial chitinase enzyme is an 18-family member, and is used by bacteria to catalyse the degradation of chitin to form products which are then used as a source of energy.
MechansimRecent studies have shown the hydrolysis of 18-family chitinase to proceed through a substrate assisted mechanism with retention of configuration in the product. A putative oxocarbonium ion intermediate is stabilised by the anchimeric assistance of the sugar N-acetyl group after the donation of a proton from the catalytic carboxylate to the departing N acetylglucosamine unit. The anionic glutamate activates a hydrolytic water by abstracting a proton, forming a hydroxide which kicks out the N-acyl group in a SN2 mechanism and forms the C1-OH group of the product. The active site is then restored.
There is no identified second carboxylate residue within the catalytic site. The protein shows low sequence homology with the 18-family chitinase enzyme collected from Hevea brasiliensis, which possesses Tyr and Asp catalytic residues, and does not share the lysozyme mechanism associated with the Heva. derived enzyme.
Reaction

Catalytic Sites for 1ctn

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
GluA315315macie:sideChainThe residue acts as a general acid to the transient oxocarbonium transition state. The resulting carboxylate group then acts as a general base towards a hydrolytic water, initiating SN2 displacement of the anchimeric N-acetyl group.

Literature References

Notes:
Fukamizo T.
Chitinolytic enzymes: catalysis, substrate binding, and their application.
Curr Protein Pept Sci 2000 1 105-124
PubMed: 12369923
Papanikolau Y
High resolution structural analyses of mutant chitinase A complexes with substrates provide new insight into the mechanism of catalysis.
Biochemistry 2001 40 11338-11343
PubMed: 11560481
Bokma E
Expression and characterization of active site mutants of hevamine, a chitinase from the rubber tree Hevea brasiliensis.
Eur J Biochem 2002 269 893-901
PubMed: 11846790
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