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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1chk

E.C. namechitosanase
SpeciesStreptomyces sp. (Bacteria)
E.C. Number (IntEnz) 3.2.1.132
CSA Homologues of 1chk1qgi,2d05,
CSA Entries With UniProtID P33665
CSA Entries With EC Number 3.2.1.132
PDBe Entry 1chk
PDBSum Entry 1chk
MACiE Entry 1chk

Literature Report

IntroductionThe enzyme chitosanase is an inverting glycoside hydrolase belonging to family 46. It catalyses the hydrolysis of chitosan, a linear polysaccharide of beta-(1,4)-linked D-glucosamine residues. Many species of soil bacteria, fungi and certain plants express chitosanases capable of degrading chitosan. The enzyme has been implicated in the resistance of E.Coli against the toxic effects of chitosan by breaking the high molecular weight polymer into short chain forms, which are non toxic to the bacteria.
MechansimThe reaction is thought to proceed through a single displacement mechanism involving an oxocarbenium ion transition state. Asp 40 acts as a general base to a structurally conserved water molecule which then attacks the substrate's anomeric carbon in an SN2 manner, with inversion of stereochemistry. Simultaneously, Glu22 acts as a general acid to the displaced polysaccharide.
Reaction

Catalytic Sites for 1chk

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AspA4080macie:sideChainThe residue acts as a general base to the hydrolytic water, enhancing its nucleophilic character.
GluA2262macie:sideChainThe residue acts as a general acid towards the departing polysaccaride during the displacement reaction, and is thought to promote the attack by the hydrolytic water molecule through its electrostatic interaction with the bridging oxygen.
ThrA4585macie:sideChainThe residue has been shown, by mutagenesis experiments and sequence homology with related enzymes to be important in directing the hydrolytic water towards the substrate anomeric carbon through hydrogen bond interactions.

Literature References

Notes:
Marcotte EM
X-ray structure of an anti-fungal chitosanase from streptomyces N174.
Nat Struct Biol 1996 3 155-162
PubMed: 8564542
Lacombe-Harvey ME
Accessory active site residues of Streptomyces sp. N174 chitosanase: variations on a common theme in the lysozyme superfamily.
FEBS J 2009 276 857-869
PubMed: 19143844
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