title: Modulation of the active site conformation by site-directed mutagenesis in cytochrome c oxidase from Paracoccus denitrificans.
abstract: The structural and functional properties of active site mutants of cytochrome c oxidase from Paracoccus denitrificans (PdCcO) were investigated with resonance Raman spectroscopy. Based on the Fe-CO stretching modes and low frequency heme modes, two conformers (alpha- and beta-forms) were identified that are in equilibrium in the enzyme. The alpha-conformer, which is the dominant species in the wild-type enzyme, has a shorter heme a(3) iron-Cu(B) distance and a more distorted heme, as compared to the beta-conformer, which has a more relaxed and open distal pocket. In general, the mutations caused a decrease in the population of the alpha-conformer, which is concomitant with a decreased in the catalytic activity, indicating that the alpha-conformer is the active form of the enzyme. The data suggest that the native structure of the enzyme is in a delicate balance of intramolecular interactions. We present a model in which the mutations destabilize the alpha-conformer, with respect to the beta-conformer, and raise the activation barrier for the inter-conversion between the two conformers. The accessibility of the two conformers in the conformational space of CcO plausibly plays a critical role in coupling the redox reaction to proton translocation during the catalytic cycle of the enzyme.
authors.affiliation: Albert Einstein College of Medicine, Department of Physiology and Biophysics, Bronx, NY 10461, United States.
authors.forename: Hong
authors.initials: H
authors.lastname: Ji
authors.forename: Tapan K
authors.initials: TK
authors.lastname: Das
authors.forename: Anne
authors.initials: A
authors.lastname: Puustinen
authors.forename: Mårten
authors.initials: M
authors.lastname: Wikström
authors.forename: Syun-Ru
authors.initials: SR
authors.lastname: Yeh
authors.forename: Denis L
authors.initials: DL
authors.lastname: Rousseau
mesh_terms: D000818:Animals; D020134:Catalytic Domain / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010231:Paracoccus denitrificans / Q000201:enzymology*; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
chemical_list: D003576:Electron Transport Complex IV