O-succinylbenzoate synthase

 

o-Succinylbenzoate synthase (OSBS) is a member of the muconate lactonising enzyme subgroup of the enolase superfamily. It catalyses the exergonic dehydration reaction in the menaquinone biosynthesis pathway in which 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate (SHCHC) is converted to o-succinylbenzoate.

 

Reference Protein and Structure

Sequence
P29208 UniProt (4.2.1.113) IPR010196 (Sequence Homologues) (PDB Homologues)
Biological species
Escherichia coli K-12 (Bacteria) Uniprot
PDB
1r6w - Crystal structure of the K133R mutant of o-Succinylbenzoate synthase (OSBS) from Escherichia coli. Complex with SHCHC (1.62 Å) PDBe PDBsum 1r6w
Catalytic CATH Domains
3.20.20.120 CATHdb (see all for 1r6w)
Cofactors
Magnesium(2+) (1)
Click To Show Structure

Enzyme Reaction (EC:4.2.1.113)

(1R,6R)-2-(3-carboxylatopropanoyl)-6-hydroxycyclohexa-2,4-diene-1-carboxylate
CHEBI:58689ChEBI
→
2-succinatobenzoate
CHEBI:18325ChEBI
+
water
CHEBI:15377ChEBI
Alternative enzyme names: o-succinylbenzoic acid synthase, OSB synthase, OSBS, 2-succinylbenzoate synthase, MenC,

Enzyme Mechanism

Introduction

The dehydration is initiated by the abstraction of a proton from the C1, the carbon adjacent to the carboxylate group by Lys133, forming an enediolate anion intermediate. The negatively charged intermediate is stabilised by Lys235 through a cation-pi interaction to the cyclohexadienyl moiety and by Mg(II) ion through a bidentate coordination to the carboxylate group. Lys133 is also responsible for protonation of the departing water molecule.

Catalytic Residues Roles

UniProt PDB* (1r6w)
Lys133 Arg133(135)A It removes a proton from C1 to initiate the dehydration. It then donates a proton to the departing water molecule. proton acceptor, proton donor
Asp161, Glu190, Asp213 Asp161(163)A, Glu190(192)A, Asp213(215)A Forms part of the magnesium binding site. metal ligand
Lys235 Lys235(237)A It stabilises the transition state by the a cation-pi interaction with the enediolate intermediate. 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

proton transfer, overall reactant used, dehydration, aromatic unimolecular elimination by the conjugate base, overall product formed, native state of enzyme regenerated

References

  1. Klenchin VA et al. (2003), Biochemistry, 42, 14427-14433. Evolution of Enzymatic Activity in the Enolase Superfamily:  Structural and Mutagenic Studies of the Mechanism of the Reaction Catalyzed byo-Succinylbenzoate Synthase fromEscherichia coli†,‡. DOI:10.1021/bi035545v. PMID:14661953.
  2. Sánchez-Tarín M et al. (2015), J Phys Chem B, 119, 1899-1911. Enzyme promiscuity in enolase superfamily. Theoretical study of o-succinylbenzoate synthase using QM/MM methods. DOI:10.1021/jp511147b. PMID:25556698.
  3. Zhu WW et al. (2012), Biochemistry, 51, 6171-6181. Residues required for activity in Escherichia coli o-succinylbenzoate synthase (OSBS) are not conserved in all OSBS enzymes. DOI:10.1021/bi300753j. PMID:22775324.
  4. Thompson TB et al. (2000), Biochemistry, 39, 10662-10676. Evolution of enzymatic activity in the enolase superfamily: structure of o-succinylbenzoate synthase from Escherichia coli in complex with Mg2+ and o-succinylbenzoate. PMID:10978150.

Step 1. Lys133 abstracts a proton from the substrate.

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Catalytic Residues Roles

Residue Roles
Lys235(237)A electrostatic stabiliser
Glu190(192)A metal ligand
Asp161(163)A metal ligand
Asp213(215)A metal ligand
Arg133(135)A proton acceptor

Chemical Components

proton transfer, overall reactant used

Step 2. The intermediate eliminates water with concomitant deprotonation of Lys133 to form the final product and regenerate the enzyme's active site.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Glu190(192)A metal ligand
Asp161(163)A metal ligand
Asp213(215)A metal ligand
Lys235(237)A electrostatic stabiliser
Arg133(135)A proton donor

Chemical Components

dehydration, proton transfer, ingold: aromatic unimolecular elimination by the conjugate base, overall product formed, native state of enzyme regenerated
Download: Image, Marvin File

Step 1. Lys133 abstracts a proton from the substrate.

Step 2. The intermediate eliminates water with concomitant deprotonation of Lys133 to form the final product and regenerate the enzyme's active site.

Products.

Contributors

Mei Leung, Gemma L. Holliday