title: Single-crystal EPR study at 95 GHz of the type 2 copper site of the inhibitor-bound quercetin 2,3-dioxygenase.
abstract: An electron-spin-echo-detected, electron-paramagnetic-resonance study has been performed on the type 2 copper site of quercetin 2,3-dioxygenase from Aspergillus japonicus. In the protein, copper is coordinated by three histidine nitrogens and two sulfurs from the inhibitor diethyldithiocarbamate. A single crystal of the protein was studied at 95 GHz and the complete g-tensor determined. The electron-paramagnetic-resonance data are compatible with two orientations of the principal g-axes in the copper center, one of which is preferred on the basis of an analysis of the copper coordination and the d-orbitals that are involved in the unpaired-electron orbital. For this orientation, the principal z-axis of the g-tensor makes an angle of 19 degrees with the Cu-N(His112) bond and the N of His112 may be considered the axial ligand. The singly occupied molecular orbital contains a linear combination of copper dxy and dyz-orbitals, which are antibonding with atomic orbitals of histidine nitrogens and diethyldithiocarbamate sulfurs. The orientation of the g-tensor for the quercetin 2,3-dioxygenase is compared with that for type 1 copper sites.
authors.affiliation: Department of Molecular Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands.
authors.forename: Maria
authors.initials: M
authors.lastname: Fittipaldi
authors.forename: Roberto A
authors.initials: RA
authors.lastname: Steiner
authors.forename: Michio
authors.initials: M
authors.lastname: Matsushita
authors.forename: Bauke W
authors.initials: BW
authors.lastname: Dijkstra
authors.forename: Edgar J J
authors.initials: EJ
authors.lastname: Groenen
authors.forename: Martina
authors.initials: M
authors.lastname: Huber
mesh_terms: D001230:Aspergillus / Q000201:enzymology; D001665:Binding Sites; D003300:Copper / Q000737:chemistry*; D049308:Dioxygenases; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006639:Histidine / Q000737:chemistry; D008024:Ligands; D008280:Magnetics; D010105:Oxygenases / Q000737:chemistry*
chemical_list: D008024:Ligands; D006639:Histidine; D003300:Copper; D010105:Oxygenases; D049308:Dioxygenases; C003281:quercetin 2,3-dioxygenase