title: Understanding the electronic properties of the CuA site from the soluble domain of cytochrome c oxidase through paramagnetic 1H NMR.
abstract: The soluble domain of the subunit II of cytochrome c oxidase from Paracoccus versutus was cloned, expressed, and studied by 1H NMR at 600 MHz. The properties of the redox-active dinuclear CuA site in the paramagnetic mixed-valence Cu(I)-Cu(II) state were investigated in detail. A group of relatively sharp signals found between 30 and 15 ppm in the 1H NMR spectrum correspond to the imidazole protons of the coordinated histidines (H181 and H224). A second group of broader and farther shifted signals between 50 and 300 ppm are assigned to Hbeta protons of the bridging cysteines (C216 and C220); the protons from the weak M227 and E218 ligands do not shift outside of the diamagnetic envelope. About 40% of the total spin density appears delocalized over the cysteine-bridging ligands while a much smaller amount is delocalized on the two ligand histidines. The latter have similar spin density distributions. Analysis of the pattern of the hyperfine shifts of the Cys H beta protons shows that the ground state bears 2B3u character, in which the sulfur lobes in the singly occupied molecular orbital are aligned with the Cu-Cu axis. Analysis of the temperature dependence of the shifts of the Cys H beta signals leads to the conclusion that the 2B2u excited state is thermally accessible at room temperature (Delta E approximately kT).
authors.affiliation: Leiden Institute of Chemistry, Leiden University, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Salgado
authors.forename: G
authors.initials: G
authors.lastname: Warmerdam
authors.forename: L
authors.initials: L
authors.lastname: Bubacco
authors.forename: G W
authors.initials: GW
authors.lastname: Canters
mesh_terms: D003300:Copper / Q000737:chemistry*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010230:Paracoccus / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D011522:Protons; D012995:Solubility; D013696:Temperature
chemical_list: D011522:Protons; D003300:Copper; D003576:Electron Transport Complex IV