Enzyme - o-succinylbenzoate synthase

Alternative Name(s)
  • OSBS.
  • 2-succinylbenzoate synthase.
  • o-succinylbenzoic acid synthase.
  • OSB synthase.

Catalytic Activity

(1R,6R)-6-hydroxy-2-succinyl-cyclohexa-2,4-diene-1-carboxylate = 2-succinylbenzoate + H2O


Mn(2+) or Mg(2+).

Reaction Mechanism

    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.

    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
    AA Uniprot Uniprot Resid PDB PDB Resid
    Lys P29208 133 1r6w 135
    Asp P29208 161 1r6w 163
    Glu P29208 190 1r6w 192
    Asp P29208 213 1r6w 215
    Lys P29208 235 1r6w 237
    Step Components

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

    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.


    The products of the reaction.

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Thermobifida fusca 0.61 (1R,6R)-6-hydroxy-2-succinylcyclohexa-2,4-diene-1-carboxylate pH 8.0, 25°C, recombinant mutant N73L/T75V
    Escherichia coli 3.8 (1R,6R)-6-hydroxy-2-succinylcyclohexa-2,4-diene-1-carboxylate pH 8.0, 25°C, recombinant mutant G288A
    Exiguobacterium sp. 2600 (1R,6R)-6-hydroxy-2-succinylcyclohexa-2,4-diene-1-carboxylate pH 8.0, 25°C, recombinant enzyme
  • Temperature
    Organism Temperature Range Comment
    Escherichia coli 37 - 60 about 30% of maximal activity at 37°C and at 60°C
  • pH
    Organism pH Range Comment
    Escherichia coli 7.5 - 9 pH 7.5: about 60% of maximal activity, pH 9.0: about 60% of maximal activity

Associated Proteins

Protein name Organism
o-succinylbenzoate synthase Escherichia coli (strain K12)
Protein PHYLLO, chloroplastic Mouse-ear cress
MenC protein Weissella cibaria
Putative o-succinylbenzoate synthase Candidatus Protochlamydia naegleriophila
Putative O-succinylbenzoate synthetase, MenC Bifidobacterium asteroides (strain PRL2011)