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Catalytic Site Atlas

CSA LITERATURE entry for 1ec9

E.C. nameglucarate dehydratase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 4.2.1.40
CSA Homologues of 1ec9There are 12 Homologs
CSA Entries With UniProtID P0AES2
CSA Entries With EC Number 4.2.1.40
PDBe Entry 1ec9
PDBSum Entry 1ec9
MACiE Entry 1ec9

Literature Report

IntroductionDelta-Glucarate dehyratase catalyses the dehydration of both D glucarate and L iarate substrates, as well as their interconversion by epimerization. The enzyme belongs to the mandelate racemase sub group of the mechanistically diverse enolase superfamily. These enzymes catalyse reactions involving the removal of an alpha proton adjacent to a carboxylate anion.
MechansimDelta-Glucarate dehyratase catalyses the dehydration of both D-Glucarate and L-Idarate to form 5-keto-4-deoxyglucarate (KDG) as well as the epimerisation of the two substrates. In the first step, the His 339 residue acts as a general base towards the C5 atom of D-Glucarate, while Lys 207 acts as a general base towards the related epimer L-Idarate. Each residue is associated with a different stereo selective function; Lys 207 acts as an S specific base, while His 339 acts as an R specific base. The enolate anion intermediate is stabilised by hydrogen bonds to residues Lys 205 and Asn 237, as well as interaction with the catalytically essential divalent Mg cation. Both the following steps, the general acid catalysed vinylogous elimination of the 4-OH group from the intermediate, generating an enol intermediate, and the general acid catalysed stereospecific tautomerisation of the enol intermediate to form the KDG product involve the His 339 residue. The use of His 339 in all three partial reactions is a good example of functional economy within enzyme catalysis.
Reaction

Catalytic Sites for 1ec9

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA339339macie:sideChainThe residue is catalytically active in all three partial reactions involving the D-Glucarate substrate, and the second two reactions when the related epimer L-Idarate is present. The residue acts as a general base towards the H bound at the C5 of the substrate, a general acid towards the enolate intermediate, resulting the in the loss of water, and then again as a general acid towards the enol intermediate, leading to stereospecific tautomerisation and formation of the KDG product.
LysA207207macie:sideChainActs as a S stereospecific general base towards the L-Idarate substrate.
LysA205205macie:sideChainThe residue hydrogen bonds to, and stabilises the enolate anion intermediate.
AsnA237237macie:sideChainThe residue hydrogen bonds to, and stabilises the enolate anion intermediate.

Literature References

Notes:
Gulick AM
Evolution of enzymatic activities in the enolase superfamily: identification of the general acid catalyst in the active site of D-glucarate dehydratase from Escherichia coli.
Biochemistry 2001 40 10054-10062
PubMed: 11513584
Gulick AM
Evolution of enzymatic activities in the enolase superfamily: crystallographic and mutagenesis studies of the reaction catalyzed by D-glucarate dehydratase from Escherichia coli.
Biochemistry 2000 39 4590-4602
PubMed: 10769114
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