title: The [2Fe-2S] cluster E(m) as an indicator of the iron-sulfur subunit position in the ubihydroquinone oxidation site of the cytochrome bc1 complex.
abstract: Recent crystallographic and kinetic data have revealed the crucial role of the large scale domain movement of the iron-sulfur subunit [2Fe-2S] cluster domain during the ubihydroquinone oxidation reaction catalyzed by the cytochrome bc(1) complex. Previously, the electron paramagnetic resonance signature of the [2Fe-2S] cluster and its redox midpoint potential (E(m)) value have been used extensively to characterize the interactions of the [2Fe-2S] cluster with the occupants of the ubihydroquinone oxidation (Q(o)) catalytic site. In this work we analyze these interactions in various iron-sulfur subunit mutants that carry mutations in its flexible hinge region. We show that the E(m) increases of the iron-sulfur subunit [2Fe-2S] cluster induced either by these mutations or by the addition of stigmatellin do not act synergistically. Moreover, the E(m) increases disappear in the presence of class I inhibitors like myxothiazol. Because various inhibitors are known to affect the location of the iron-sulfur subunit cluster domain, the measured E(m) value of the [2Fe-2S] cluster therefore reflects its equilibrium position in the Q(o) site. We also demonstrate the existence in this site of a location where the E(m) of the cluster is increased by about 150 mV and discuss its possible implications in term of Q(o) site catalysis and energetics.
authors.affiliation: Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Darrouzet
authors.forename: Maria
authors.initials: M
authors.lastname: Valkova-Valchanova
authors.forename: Fevzi
authors.initials: F
authors.lastname: Daldal
mesh_terms: D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D014450:Electron Transport Complex III / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D010084:Oxidation-Reduction; D011199:Potentiometry; D011487:Protein Conformation; D021122:Protein Subunits; D016354:Rhodobacter capsulatus / Q000378:metabolism
chemical_list: D007506:Iron-Sulfur Proteins; D021122:Protein Subunits; D014450:Electron Transport Complex III