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Catalytic Site Atlas

CSA LITERATURE entry for 1gog

E.C. namegalactose oxidase
SpeciesDactylium dendroides ()
E.C. Number (IntEnz) 1.1.3.9
CSA Homologues of 1gogThere are 11 Homologs
CSA Entries With UniProtID Q01745
CSA Entries With EC Number 1.1.3.9
PDBe Entry 1gog
PDBSum Entry 1gog
MACiE Entry M0322

Literature Report

IntroductionGalactose oxidase is a copper containing enzyme which oxidises primary alcohols to aldehydes by the reduction of molecular oxygen to hydrogen peroxide. It contains a novel metalloradical complex, formed by a unique structural feature at the copper site with a novel thioether bond linking Cys 228 and Tyr 272 formed from a post-translational modification, which is in a stacking interaction with Trp 290. Galactose oxidase is remarkable in the extent to which free radicals are involved in all aspects of the enzyme function: serving as a key feature of the active site structure, defining the characteristic reactivity of the complex, and directing the biogenesis of the Tyr-Cys cofactor during protein maturation.
MechansimIn the first (reductive) half-reaction, the oxidized free radicals Cu2+ complex reacts with the primary alcohol. The initial proton abstraction from a coordinated substrate activates the alcohol toward inner sphere electron transfer to the Cu(II) metal centre in an unfavourable redox equilibrium, forming an alkoxy radical which undergoes hydrogen atom abstraction by the tyrosine-cysteine phenoxyl free radical ligand to form the product aldehyde. In the second (oxidative) half-reaction, the reduced enzyme reacts with dioxygen , converting the active site to the metalloradical complex and forming hydrogen peroxide. A two-electron oxidation performed by a single copper ion- is explained by the involvement of another redox center, namely a tyrosyl radical from the protein, during the catalytic cycle. Extensive characterizations have shown, that it is located at Tyr272.
Reaction

Catalytic Sites for 1gog

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
TyrA495536macie:sideChainTyr495 serves as a general base that activates the reducing substrate by proton abstraction during the reductive half-reaction, and facilitates displacement of hydrogen peroxide product by protonation in the oxidative half-reaction.
TrpA290331macie:sideChainThe active site tryptophan (Trp290), which lies over the Tyr–Cys cofactor with the indole nitrogen adjacent to the coordinated oxygen of the Tyr272 side chain may play a role in the stabilization of the substrate-derived proton in this complex. It is pi-stacked to try-cys moiety and also controls entry to the active site.
CysA228269macie:sideChainForms a thioether cross link with Tyr272- see the functional notes for more details on its action.
TyrA272313macie:sideChainThe Try272 forms a cross link to Cys228, which coordinates to copper to form a metalloradical complex in the oxidized, active form of the enzyme This free radical-coupled copper complex is extremely stable. It reacts readily with a variety of electron donors, undergoing single-electron reduction to form a catalytically inactive non-radical–Cu2+ complex. Further reduction converts the Cu2+ centre to Cu1+, forming a fully reduced complex that is competent for reaction with O2 and represents a catalytic intermediate in the reaction. The reactivity of the Cys-Tyr cofactor may be reflected in its lower O- H bond dissociation energy in its reduced form, facilitating hydrogen atom donation to O2 during catalysis The orientation of Tyr272 also maximizes overlap between the redox orbital on the phenoxyl oxygen and the half-occupied d-orbital on Cu, reflected in a strong antiferromagnetic exchange splitting in the electronic ground state of the complex.

Literature References

Notes:
F Himo,LA Eriksson,F Maseras,PEM Siegbahn
Catalytic Mechanism of Galactose Oxidase: A Theoretical Study
J. Am. Chem. Soc. 2000 122 8031-8036
PubMed: Himo2000
Lee YK
The electronic structure of the Cys-Tyr(*) free radical in galactose oxidase determined by EPR spectroscopy.
Biochemistry 2008 47 6637-6649
PubMed: 18512952
Ito N
Novel thioether bond revealed by a 1.7 A crystal structure of galactose oxidase.
Nature 1991 350 87-90
PubMed: 2002850
Humphreys KJ
Galactose oxidase as a model for reactivity at a copper superoxide center.
J Am Chem Soc 2009 131 4657-4663
PubMed: 19290629
Ito N.
Crystal structure of a free radical enzyme, galactose oxidase
J Mol Biol 1994 238 794-814
PubMed: 8182749
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