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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1bou

E.C. nameprotocatechuate 4,5-dioxygenase
SpeciesPseudomonas paucimobilis (Sphingomonas paucimobilis)
E.C. Number (IntEnz) 1.13.11.8
CSA Homologues of 1bou1b4u,2pw6,
CSA Entries With UniProtID P22635
CSA Entries With EC Number 1.13.11.8
PDBe Entry 1bou
PDBSum Entry 1bou
MACiE Entry 1bou

Literature Report

IntroductionThe LigAB enzyme from Sphingomonas paucimobilis SYK-6 is a protocatechuate 4,5-dioxygenase, catalyses the ring-opening of protocatechuate(PCA) by oxidation to cleave the C4-C5 bond adjacent to the vicinal hydroxyl group. It belongs to the family of class III extradiol-type catecholic dioxygenase which is characterised by a ferrous iron in the active site. It has been identified as a key enzyme in the lignin-degradation pathway of S.paucimobilis SYK-6.
MechansimBased on the common features around the active sites of BphC, a class II extradiol-type catacholic dioxygenase, and LigAB, it was suggested that LigAB has the same catalytic mechanism as BphC.
The 2 hydroxyl groups of PCA chelate the Fe(II) centre with only one proton lost upon binding of the substrate. Binding of the substrate anion to the Fe(II) activates it to bind dioxygen at the vacant sixth coordination site. O2 binding results in the transfer of charge from Fe(II) to O2, forming an Fe(III)-superoxide species. A subsequent shift of electron density from coordinates PCA to the iron centre enhances the nucleophilic attack of the nascent superoxide on the PCA ring to form an intermediate alkylperoxo moiety. Cleavage of the O-O bond, coupled with a ring insertion reaction with His195b as the base catalyst, forms a seven-membered lactone ring. Hydrolysis of the lactone ring yields a semialdehyde product.
Reaction

Catalytic Sites for 1bou

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisB195195macie:sideChainIt acts as a base to deprotonate the C4-hydroxyl group in the reaction.

Annotated By Reference To The Literature - Site 2 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisD195195macie:sideChainIt acts as a base to deprotonate the C4-hydroxyl group in the reaction.

Literature References

Notes:
Sugimoto K
Crystal structure of an aromatic ring opening dioxygenase LigAB, a protocatechuate 4,5-dioxygenase, under aerobic conditions.
Structure 1999 7 953-965
PubMed: 10467151
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