title: Redox thermodynamics of high-spin and low-spin forms of chlorite dismutases with diverse subunit and oligomeric structures.
abstract: Chlorite dismutases (Clds) are heme b-containing oxidoreductases that convert chlorite to chloride and dioxygen. In this work, the thermodynamics of the one-electron reduction of the ferric high-spin forms and of the six-coordinate low-spin cyanide adducts of the enzymes from Nitrobacter winogradskyi (NwCld) and Candidatus "Nitrospira defluvii" (NdCld) were determined through spectroelectrochemical experiments. These proteins belong to two phylogenetically separated lineages that differ in subunit (21.5 and 26 kDa, respectively) and oligomeric (dimeric and pentameric, respectively) structure but exhibit similar chlorite degradation activity. The E°' values for free and cyanide-bound proteins were determined to be -119 and -397 mV for NwCld and -113 and -404 mV for NdCld, respectively (pH 7.0, 25 °C). Variable-temperature spectroelectrochemical experiments revealed that the oxidized state of both proteins is enthalpically stabilized. Molecular dynamics simulations suggest that changes in the protein structure are negligible, whereas solvent reorganization is mainly responsible for the increase in entropy during the redox reaction. Obtained data are discussed with respect to the known structures of the two Clds and the proposed reaction mechanism.
authors.affiliation: Department of Chemistry, Division of Biochemistry, VIBT-Vienna Institute of BioTechnology, BOKU-University of Natural Resources and Life Sciences, A-1190 Vienna, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hofbauer
authors.forename: Marzia
authors.initials: M
authors.lastname: Bellei
authors.forename: Axel
authors.initials: A
authors.lastname: Sündermann
authors.forename: Katharina F
authors.initials: KF
authors.lastname: Pirker
authors.forename: Andreas
authors.initials: A
authors.lastname: Hagmüller
authors.forename: Georg
authors.initials: G
authors.lastname: Mlynek
authors.forename: Julius
authors.initials: J
authors.lastname: Kostan
authors.forename: Holger
authors.initials: H
authors.lastname: Daims
authors.forename: Paul G
authors.initials: PG
authors.lastname: Furtmüller
authors.forename: Kristina
authors.initials: K
authors.lastname: Djinović-Carugo
authors.forename: Chris
authors.initials: C
authors.lastname: Oostenbrink
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Christian
authors.initials: C
authors.lastname: Obinger
mesh_terms: D020134:Catalytic Domain; D002712:Chlorides; D004578:Electron Spin Resonance Spectroscopy; D019277:Entropy; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009576:Nitrobacter / Q000201:enzymology; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D013816:Thermodynamics
chemical_list: D002712:Chlorides; D005290:Ferric Compounds; D005296:Ferrous Compounds; D010088:Oxidoreductases; C402794:chlorite dismutase; C001599:chlorite