title: Redox thermodynamics of the ferric-ferrous couple of wild-type synechocystis KatG and KatG(Y249F).
abstract: Crystal structures and mass spectrometric analyses of catalase-peroxidases (KatGs) from different organisms revealed the existence of a peculiar distal Met-Tyr-Trp cross-link. The adduct appears to be important for the catalase but not the peroxidase activity of bifunctional KatG. To examine the effect of the adduct on enzyme redox properties and functions, we have determined the thermodynamics of ferric reduction for wild-type KatG and KatG(Y249F), whose tyrosine-to-phenylalanine mutation prevents cross-link formation. At 25 degrees C and pH 7.0, the reduction potential of wild-type KatG is found to be -226 +/- 10 mV, remarkably lower than the published literature values. The reduction potential of KatG(Y249F) is very similar (-222 +/- 10 mV), but variable temperature experiments revealed compensatory differences in reduction enthalpies and entropies. In both proteins, the oxidized state is enthalpically stabilized over the reduced state, but entropy is lost on reduction, which is in strong contrast to horseradish peroxidase, which also features a much more pronounced enthalpic stabilization of the ferriheme. With both proteins, the midpoint potential increased linearly with decreasing pH. We discuss whether the observed redox thermodynamics reflects the differences in structure and function between bifunctional KatG and monofunctional peroxidases.
authors.affiliation: Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.
authors.forename: Marzia
authors.initials: M
authors.lastname: Bellei
authors.forename: Christa
authors.initials: C
authors.lastname: Jakopitsch
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Marco
authors.initials: M
authors.lastname: Sola
authors.forename: Christian
authors.initials: C
authors.lastname: Obinger
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D004563:Electrochemistry; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D046939:Synechocystis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D005290:Ferric Compounds; D005296:Ferrous Compounds; D006418:Heme; D010544:Peroxidases; C081610:catalase-peroxidase, bacteria