title: Correlating the structures and activities of the resting oxidized and native intermediate states of a small laccase by paramagnetic NMR.
abstract: Multicopper oxidases (MCO) are the fastest and most efficient known catalysts of the oxygen-reduction reaction. When all four copper ions are oxidized during catalysis, the native intermediate state (NI) decays in seconds to the resting oxidized state (RO), which returns to the catalytic cycle via reduction, but at a much slower rate than NI. We report the long-lived (months at 4°C) NI state of the small laccase (SLAC) MCO and the subsequent characterization of both its RO and NI states by paramagnetic (1)H NMR. We find that the RO state of the trinuclear cluster (TNC) is best described as an isolated Type-3 dicopper site, antiferromagnetically coupled by a hydroxo group with -2J=500cm(-1). The NI state is more complicated; we develop a theoretical treatment for the case in which all three copper ions in the TNC are coupled, and find that the results are consistent with three coupling constants of -2J=300, 240, and 160cm(-1). These couplings result in a ground doublet state, a low-lying excited doublet state at 121cm(-1), and a quartet excited state at 411cm(-1), in good agreement with DFT models in which the Type-2 copper has a terminal hydroxo ligand.
authors.affiliation: Department of Chemistry, State University of New York at New Paltz, 1 Hawk Drive, New Paltz, NY, 12561, United States. Electronic address: machczym@newpaltz.edu.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Machczynski
authors.affiliation: Department of Chemistry, State University of New York at New Paltz, 1 Hawk Drive, New Paltz, NY, 12561, United States.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Babicz
mesh_terms: D003300:Copper / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D042845:Laccase / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular
chemical_list: D029968:Escherichia coli Proteins; D003300:Copper; D042845:Laccase
keywords: Copper; Exchange coupling; Laccase; Native intermediate; Oxidase; Paramagnetic NMR