Structural snapshots from the oxidative half-reaction of a copper amine oxidase: implications for O2 activation

The mechanism of molecular oxygen activation is the subject of controversy in the copper amine oxidase family. At their active sites, copper amine oxidases contain both a mononuclear copper ion and a protein-derived quinone cofactor. Proposals have been made for the activation of molecular oxygen vi...

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Bibliographic Details
Published inThe Journal of biological chemistry Vol. 288; no. 39; p. 28409
Main Authors Johnson, Bryan J, Yukl, Erik T, Klema, Valerie J, Klinman, Judith P, Wilmot, Carrie M
Format Journal Article
LanguageEnglish
Published United States 27.09.2013
Subjects
Amine Oxidase (Copper-Containing) - chemistry
Ascomycota - metabolism
Catalysis
Copper - chemistry
Crystallography, X-Ray
Electron Transport
Hydrogen Peroxide - chemistry
Hydrogen-Ion Concentration
Hydroquinones - chemistry
Models, Chemical
Oxidation-Reduction
Oxygen - chemistry
Quinones - chemistry
Spectrophotometry
Enzyme Mechanisms
Quinones
Spectroscopy
Oxidation-Reduction
X-ray Crystallography
Oxygen Binding
Copper
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Summary:The mechanism of molecular oxygen activation is the subject of controversy in the copper amine oxidase family. At their active sites, copper amine oxidases contain both a mononuclear copper ion and a protein-derived quinone cofactor. Proposals have been made for the activation of molecular oxygen via both a Cu(II)-aminoquinol catalytic intermediate and a Cu(I)-semiquinone intermediate. Using protein crystallographic freeze-trapping methods under low oxygen conditions combined with single-crystal microspectrophotometry, we have determined structures corresponding to the iminoquinone and semiquinone forms of the enzyme. Methylamine reduction at acidic or neutral pH has revealed protonated and deprotonated forms of the iminoquinone that are accompanied by a bound oxygen species that is likely hydrogen peroxide. However, methylamine reduction at pH 8.5 has revealed a copper-ligated cofactor proposed to be the semiquinone form. A copper-ligated orientation, be it the sole identity of the semiquinone or not, blocks the oxygen-binding site, suggesting that accessibility of Cu(I) may be the basis of partitioning O2 activation between the aminoquinol and Cu(I).
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ISSN:1083-351X
1083-351X
DOI:10.1074/jbc.M113.501791