Chitinase C

 

Chitinase C (ChiC) from Streptomyces griseus HUT6037 catalysis the hydrolysis of N-acetyl-beta-D-glucosaminide 1,4-beta-linkages in chitin yielding alpha-anomeric products. It is a member of family 19 of glycoside hydrolases. Bacteria that break down chitin can use it as a source of carbon.

 

Reference Protein and Structure

Sequence
O50152 UniProt IPR016283 (Sequence Homologues) (PDB Homologues)
Biological species
Streptomyces griseus (Bacteria) Uniprot
PDB
2dbt - Crystal structure of chitinase C from Streptomyces griseus HUT6037 (3.14 Å) PDBe PDBsum 2dbt
Catalytic CATH Domains
3.30.20.10 CATHdb 1.10.530.10 CATHdb (see all for 2dbt)
Click To Show Structure

Enzyme Reaction (EC:3.2.1.14)

N-acetyl-beta-D-glucosaminyl-(1->4)-N-acetyl-beta-D-glucosamine
CHEBI:50670ChEBI
+
water
CHEBI:15377ChEBI
→
N-acetyl-D-glucosamine
CHEBI:506227ChEBI
+
N-acetyl-D-glucosamine
CHEBI:506227ChEBI
Alternative enzyme names: 1,4-beta-poly-N-acetylglucosaminidase, Beta-1,4-poly-N-acetyl glucosamidinase, Chitodextrinase, Poly-beta-glucosaminidase, Poly(1,4-(N-acetyl-beta-D-glucosaminide)) glycanohydrolase, ChiC,

Enzyme Mechanism

Introduction

For family 19 chitinases the hydrolysis proceeds via an oxocarbenium ion intermediate and the product has an inversion of the anomeric configuration. The beta-(1,4)glycosidic oxygen is protonated by Glu147. Glu156 acts as the general base. It deprotonates a water molecule which acts as a nucleophile and attacks the C1 carbon of a pyranose ring on the substrate to form the oxocarbenium ion.

Catalytic Residues Roles

UniProt PDB* (2dbt)
Glu147 Glu147(118)A Acts as a general acid, protonates the beta-(1,4)glycosidic oxygen. promote heterolysis, proton acceptor, proton donor
Glu156 Glu156(127)A Acts as general base, deprotonates a water molecule which acts as the nucleophile. Glu156 also helps stabilise the oxocarbenium ion. proton acceptor, proton donor, activator, electrostatic stabiliser, increase nucleophilicity
Asn194 Asn194(165)A Forms hydrogen bonds to the N-acetyl group of sugar D forcing an extended geometry and preventing the formation of an oxazoline ion intermediate. steric role
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

proton transfer, overall product formed, overall reactant used, heterolysis, bimolecular nucleophilic addition, inferred reaction step, native state of enzyme regenerated

References

  1. Kezuka Y et al. (2006), J Mol Biol, 358, 472-484. Structural Studies of a Two-domain Chitinase from Streptomyces griseus HUT6037. DOI:10.1016/j.jmb.2006.02.013. PMID:16516924.
  2. Brameld KA et al. (1998), Proc Natl Acad Sci U S A, 95, 4276-4281. The role of enzyme distortion in the single displacement mechanism of family 19 chitinases. DOI:10.1073/pnas.95.8.4276. PMID:9539727.
  3. Andersen MD et al. (1997), Biochem J, 322, 815-822. Heterologous expression and characterization of wild-type and mutant forms of a 26 kDa endochitinase from barley (Hordeum vulgareL.). DOI:10.1042/bj3220815. PMID:9148754.

Step 1. Glu147 protonates the glycosidic bond this causes the bond to be cleaved with the formation of an oxocarbenium ion.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Glu156(127)A electrostatic stabiliser
Asn194(165)A steric role
Glu147(118)A promote heterolysis, proton donor

Chemical Components

proton transfer, overall product formed, overall reactant used, heterolysis

Step 2. Glu156 activates a water molecule which attacks the oxocarbenium ion.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Glu156(127)A activator, increase nucleophilicity
Asn194(165)A steric role
Glu156(127)A proton acceptor

Chemical Components

ingold: bimolecular nucleophilic addition, proton transfer, overall product formed
Download: Image, Marvin File

Step 4. Inferred step- active site is regenerated.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Glu156(127)A proton donor
Glu147(118)A proton acceptor

Chemical Components

inferred reaction step, proton transfer, native state of enzyme regenerated

Step 1. Glu147 protonates the glycosidic bond this causes the bond to be cleaved with the formation of an oxocarbenium ion.

Step 2. Glu156 activates a water molecule which attacks the oxocarbenium ion.

Products.

Step 4. Inferred step- active site is regenerated.

Contributors

Gemma L. Holliday, James Willey