4-hydroxy-2-oxovalerate aldolase

 

4-hydroxy-2-ketovalerate aldolase catalyses the conversion of 4-hydroxy-2-ketovalerate to acetaldehyde and pyruvate. It associates tightly with acetaldehyde dehydrogenase and appears to be inactive when expressed without this dehydrogenase. The aldolase and dehydrogenase form a bifunctional enzyme, and there is evidence that the reactive acetaldehyde intermediate is passed between the two active sites via a channelling tunnel. the bifunctional enzyme catalyses the final two steps in the degradation of catechol, an intermediate in the degradation of aromatic compounds by many bacteria.

 

Reference Protein and Structure

Sequences
P51016 UniProt (4.1.3.39)
Q52060 UniProt (1.2.1.10) IPR017629 (Sequence Homologues) (PDB Homologues)
Biological species
Pseudomonas sp. CF600 (Bacteria) Uniprot
PDB
1nvm - Crystal structure of a bifunctional aldolase-dehydrogenase : sequestering a reactive and volatile intermediate (1.7 Å) PDBe PDBsum 1nvm
Catalytic CATH Domains
3.20.20.70 CATHdb 1.10.8.60 CATHdb (see all for 1nvm)
Cofactors
Water (1), Manganese(2+) (1)
Click To Show Structure

Enzyme Reaction (EC:4.1.3.39)

(S)-4-hydroxy-2-oxopentanoate
CHEBI:73143ChEBI
→
pyruvate
CHEBI:15361ChEBI
+
acetaldehyde
CHEBI:15343ChEBI
Alternative enzyme names: 4-hydroxy-2-ketovalerate aldolase, HOA, DmpG, 4-hydroxy-2-oxovalerate pyruvate-lyase, 4-hydroxy-2-oxopentanoate pyruvate-lyase, 4-hydroxy-2-oxopentanoate pyruvate-lyase (acetaldehyde-forming),

Enzyme Mechanism

Introduction

The proposed catalytic mechanism involves His 21 acting as a base to remove a proton from the 4-hydroxyl group. Concomitant cleavage of the C3-C4 bond leads to formation of acetaldehyde and the enolate of pyruvate. Accumulation of negative charge on the 2-carbonyl oxygen during formation of the enolate is stabilised by an Mn2+ ion. The enolate is protonated on C3 by Tyr 291 (which is later re-protonated by His 21) to form pyruvate, while the acetaldehyde is passed to the dehydrogenase active site via a tunnel. Access to this tunnel is proposed to be controlled by movements of Tyr 291 during the catalytic cycle.

Catalytic Residues Roles

UniProt PDB* (1nvm)
Asp18, His200, His202 Asp18A, His200A, His202A Coordinate the metal ligand. metal ligand
His21 His21A Deprotonates the 4-hydroxyl group of the substrate, leading to generation of acetalydehyde and the enolate of pyruvate. Later protonates Tyr 291. proton acceptor, proton donor
Tyr291 Tyr291A Protonates the methylene group of the enolate of pyruvate. Regains a proton from His 21. proton acceptor, proton donor
*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, bimolecular elimination, overall reactant used, overall product formed, assisted keto-enol tautomerisation, native state of enzyme regenerated

References

  1. Manjasetty BA et al. (2003), Proc Natl Acad Sci U S A, 100, 6992-6997. Crystal structure of a bifunctional aldolase-dehydrogenase: Sequestering a reactive and volatile intermediate. DOI:10.1073/pnas.1236794100. PMID:12764229.

Step 1. His 21 acts as a base and deprotonates the C4 hydroxyl group. The concomitant bond cleavage of the C3-C4 bond leads to the formation of acetaldehyde and the enolate of pyruvate.

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Catalytic Residues Roles

Residue Roles
Asp18A metal ligand
His200A metal ligand
His202A metal ligand
His21A proton acceptor

Chemical Components

proton transfer, ingold: bimolecular elimination, overall reactant used, overall product formed

Step 2. Tyr291 accepts a proton from His21.

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Catalytic Residues Roles

Residue Roles
Asp18A metal ligand
His200A metal ligand
His202A metal ligand
Tyr291A proton acceptor
His21A proton donor

Chemical Components

proton transfer

Step 3. The enolate is then protonated by Tyr291 and pyruvate is released.

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Catalytic Residues Roles

Residue Roles
Asp18A metal ligand
His200A metal ligand
His202A metal ligand
Tyr291A proton donor

Chemical Components

assisted keto-enol tautomerisation, proton transfer, overall product formed, native state of enzyme regenerated
Download: Image, Marvin File

Step 1. His 21 acts as a base and deprotonates the C4 hydroxyl group. The concomitant bond cleavage of the C3-C4 bond leads to the formation of acetaldehyde and the enolate of pyruvate.

Step 2. Tyr291 accepts a proton from His21.

Step 3. The enolate is then protonated by Tyr291 and pyruvate is released.

Products.

Contributors

Steven Smith, Gemma L. Holliday, James Willey