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Catalytic Site Atlas

CSA LITERATURE entry for 1a8q

E.C. namechloride peroxidase
SpeciesStreptomyces aureofaciens (Bacteria)
E.C. Number (IntEnz) 1.11.1.10
CSA Homologues of 1a8q
CSA Entries With UniProtID
CSA Entries With EC Number 1.11.1.10
PDBe Entry 1a8q
PDBSum Entry 1a8q
MACiE Entry 1a8q

Literature Report

IntroductionBacterial cofactor-free haloperoxidases can halogenate organic compounds in the presence of halide ions and peroxides such as H2O2. They can often utilise several halide ions, and are named after the most electronegative halide they can oxidise.
MechansimCofactor-free bromoperoxidase is thought to catalyse the formation of a peroxy acid from a carboxylic acid. The next steps in the overall reaction are thought to be formation of hypobromic acid and then halogenation of the organic compound. These steps are not catalysed specifically by the enzyme, but the active pocket may provide a suitable environment for the reaction - eg, protection against hydrolysis, favourable environment hydrophobicity.
The enzyme employs a classic serine protease mechanism (Ser 94, His 252, Asp 223) to acylate Ser 94 with an organic acid, releasing water (the protons of the water come from the serine and a specific acid in the active site).
Hydrogen peroxide can then nucleophilically attack the acyl-enzyme, regenerating free Ser 94 and a peroxy acid.
Reaction

Catalytic Sites for 1a8q

Annotated By Reference To The Literature - Site 2 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
TrpA2829macie:mainChainAmideThe backbone amide of Trp 28 acts as an oxyanion hole, stabilising the charge on the tetrahedral transition states and intermediates.
MetA9596macie:mainChainAmideThe backbone amide of Met 95 acts as an oxyanion hole, stabilising the charge on the tetrahedral transition states and intermediates.
AspA223224macie:sideChainAsp 223 is the Asp of the classic Ser-His-Asp catalytic triad, polarising His 252 so that it can polarise Ser 94.
SerA9495macie:sideChainSer 94 is the nucleophile of the Ser-His-Asp triad. Its hydroxy group attacks the carboxylic acid substrate, forming an acyl-enzyme intermediate. Attack of H2O2 regenerates Ser 94.
HisA252253macie:sideChainHis 252 hydrogen bonds to Ser 94, making the hydroxyl group more nucleophilic.
In contrast to the classic Ser-His-Asp, His 252 is not thought to retain the proton from Ser 94, as this proton is required to create the water leaving group from the carboxylic acid.

Literature References

Notes:It is possible that hydrogen peroxide attacks the tetrahedral intermediate formed from attack of Ser 94 on the carboxylic acid, instead of the acyl-enzyme.
Hofmann B
Structural investigation of the cofactor-free chloroperoxidases.
J Mol Biol 1998 279 889-900
PubMed: 9642069
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