Muconate cycloisomerase (syn)

 

Catalyses the syn cycloisomerisation of +-muconolactone to cis-cis-muconate. Involved in the second step of the subpathway that synthesizes 5-oxo-4,5-dihydro-2-furylacetate from catechol.

 

Reference Protein and Structure

Sequence
Q4K9X1 UniProt (5.5.1.1) IPR013370 (Sequence Homologues) (PDB Homologues)
Biological species
Pseudomonas protegens Pf-5 (Bacteria) Uniprot
PDB
3dgb - Crystal structure of muconate lactonizing enzyme from Pseudomonas Fluorescens complexed with muconolactone (1.7 Å) PDBe PDBsum 3dgb
Catalytic CATH Domains
3.30.390.10 CATHdb 3.20.20.120 CATHdb (see all for 3dgb)
Cofactors
Manganese(2+) (1) Metal MACiE
Click To Show Structure

Enzyme Reaction (EC:5.5.1.1)

cis,cis-muconate
CHEBI:32379ChEBI
+
hydron
CHEBI:15378ChEBI
→
(S)-5-oxo-2,5-dihydro-2-furylacetate
CHEBI:58736ChEBI
Alternative enzyme names: 4-carboxymethyl-4-hydroxyisocrotonolactone lyase (decyclizing), Cis,cis-muconate cycloisomerase, Cis,cis-muconate-lactonizing enzyme, Muconate cycloisomerase I, Muconate lactonizing enzyme, Cis,cis-muconate lactonizing enzyme I, CatB, MCl, 2,5-dihydro-5-oxofuran-2-acetate lyase (decyclizing),

Enzyme Mechanism

Introduction

Catalyses an addition of the C1 carboxylate oxygen in substrate, muconate, to the C4 double-bonded carbon, and an isomerisation, through an enolate intermediate.

Catalytic Residues Roles

UniProt PDB* (3dgb)
Lys273 Lys275A Acts to stabilise the enolate anion intermediate. electrostatic stabiliser
Asp198, Glu224, Asp249 Asp200A, Glu226A, Asp251A Forms manganese binding site. metal ligand
His22 His24A Enforces the rotamer position such that the enzyme works on the syb-face of the substrate. steric role
Glu327, Lys169 Glu329A, Lys171A Acts as a general acid/base. proton acceptor, proton donor
Lys167 Lys169A Stabilises the transition state. electrostatic stabiliser
*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

intramolecular nucleophilic addition, assisted keto-enol tautomerisation, cyclisation, intermediate formation, overall reactant used, proton transfer, intermediate terminated, overall product formed

References

  1. Sakai A et al. (2009), Biochemistry, 48, 1445-1453. Evolution of Enzymatic Activities in the Enolase Superfamily: Stereochemically Distinct Mechanisms in Two Families ofcis,cis-Muconate Lactonizing Enzymes†‡. DOI:10.1021/bi802277h. PMID:19220063.
  2. Somboon T et al. (2012), J Mol Model, 18, 525-531. Insight into the reaction mechanism of cis,cis-muconate lactonizing enzymes: a DFT QM/MM study. DOI:10.1007/s00894-011-1088-2. PMID:21541743.
  3. Kajander T et al. (2003), Protein Sci, 12, 1855-1864. The structure ofPseudomonasP51 Cl-muconate lactonizing enzyme: Co-evolution of structure and dynamics with the dehalogenation function. DOI:10.1110/ps.0388503. PMID:12930985.
  4. Cha CJ et al. (2003), FEMS Microbiol Lett, 224, 29-34. Stereo- and regiospecific cis,cis-muconate cycloisomerization by Rhodococcus rhodochrous N75. PMID:12855164.
  5. Schell U et al. (1999), Proteins, 34, 125-136. Structural basis for the activity of two muconate cycloisomerase variants toward substituted muconates. DOI:10.1002/(sici)1097-0134(19990101)34:1<125::aid-prot10>3.3.co;2-p. PMID:10336378.
  6. Hasson MS et al. (1998), Proc Natl Acad Sci U S A, 95, 10396-10401. Evolution of an enzyme active site: The structure of a new crystal form of muconate lactonizing enzyme compared with mandelate racemase and enolase. DOI:10.1073/pnas.95.18.10396. PMID:9724714.
  7. Helin S et al. (1995), J Mol Biol, 254, 918-941. The Refined X-ray Structure of Muconate Lactonizing Enzyme fromPseudomonas putidaPRS2000 at 1.85 Å Resolution. DOI:10.1006/jmbi.1995.0666. PMID:7500361.
  8. Babbitt PC et al. (1995), Science, 267, 1159-1161. A functionally diverse enzyme superfamily that abstracts the alpha protons of carboxylic acids. PMID:7855594.
  9. Neidhart DJ et al. (1990), Nature, 347, 692-694. Mandelate racemase and muconate lactonizing enzyme are mechanistically distinct and structurally homologous. DOI:10.1038/347692a0. PMID:2215699.

Step 1. The C1 carboxylate initiates a nucleophilic attack on the C4 double bond, initiating double bond rearrangement and forming the enol intermediate.

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Catalytic Residues Roles

Residue Roles
Asp200A metal ligand
Glu226A metal ligand
Asp251A metal ligand
His24A steric role
Lys169A electrostatic stabiliser
Lys171A electrostatic stabiliser
Lys275A electrostatic stabiliser
Glu329A proton donor

Chemical Components

ingold: intramolecular nucleophilic addition, assisted keto-enol tautomerisation, cyclisation, intermediate formation, overall reactant used, proton transfer

Step 2. Glu329 deprotonates the enol resulting in the protonation of C5, supplied by Lys171, to produce the cyclic non-planar product. At the end of this step the enzyme is in the correct state to perform the reverse reaction.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Asp200A metal ligand
Glu226A metal ligand
Asp251A metal ligand
His24A steric role
Lys275A electrostatic stabiliser
Lys169A electrostatic stabiliser
Glu329A proton acceptor
Lys171A proton donor

Chemical Components

intermediate terminated, overall product formed, proton transfer
Download: Image, Marvin File

Step 1. The C1 carboxylate initiates a nucleophilic attack on the C4 double bond, initiating double bond rearrangement and forming the enol intermediate.

Step 2. Glu329 deprotonates the enol resulting in the protonation of C5, supplied by Lys171, to produce the cyclic non-planar product. At the end of this step the enzyme is in the correct state to perform the reverse reaction.

Products.

Contributors

Gemma L. Holliday, Alex Gutteridge, Craig Porter