Structures of Metal Sites of Oxidized Bovine Heart Cytochrome c Oxidase at 2.8 Å

Abstract

The high resolution three-dimensional x-ray structure of the metal sites of bovine heart cytochrome c oxidase is reported. Cytochrome c oxidase is the largest membrane protein yet crystallized and analyzed at atomic resolution. Electron density distribution of the oxidized bovine cytochrome c oxidase at 2.8 A resolution indicates a dinuclear copper center with an unexpected structure similar to a [2Fe-2S]-type iron-sulfur center. Previously predicted zinc and magnesium sites have been located, the former bound by a nuclear encoded subunit on the matrix side of the membrane, and the latter situated between heme a3 and CuA, at the interface of subunits I and II. The O2 binding site contains heme a3 iron and copper atoms (CuB) with an interatomic distance of 4.5 A; there is no detectable bridging ligand between iron and copper atoms in spite of a strong antiferromagnetic coupling between them. A hydrogen bond is present between a hydroxyl group of the hydroxyfarnesylethyl side chain of heme a3 and an OH of a tyrosine. The tyrosine phenol plane is immediately adjacent and perpendicular to an imidazole group bonded to CuB, suggesting a possible role in intramolecular electron transfer or conformational control, the latter of which could induce the redox-coupled proton pumping. A phenyl group located halfway between a pyrrole plane of the heme a3 and an imidazole plane liganded to the other heme (heme a) could also influence electron transfer or conformational control.

Metal Ion availability in mitochondria

“…Within the mitochondrion, copper is required for assembly of CcO and superoxide dismutase (Sod1) (Sturtz et al 2001;Tsukihara et al 1995). Two mitochondrially-encoded subunits of CcO have copper centers.…”

Carboxyl group protonation upon reduction of the Paracoccus denitrificans cytochrome c oxidase: direct evidence by FTIR spectroscopy

“…Recently, structural information from X-ray crystallography on the complete Paracoccus denitrtjicans oxidase [4] and on the cofactors of beef-heart oxidase [5] has put discussions on the catalytic and proton transfer mechanism of this enzyme on new grounds. The previously proposed pathway of the electrons from the cytochrome c docking site to CUA and via heme a to the binuclear site formed by Cue and heme a3 is now solidly established by the high-resolution X-ray structure [4], and two pathways for protons appear possible (for a detailed discussion, see [4]).…”

A structural moDAl for the membrane‐integral domain of succinate:quinone oxidoreductases

“…SQR in many organisms contains cytochrome of b-type [1,2]. The function and structure of this cytochrome is poorly understood as compared to that of the cytochrome bc/bf (complex III, quinol:cytochrome c reductase) and cytochrome c oxidase (complex IV) [3][4][5].…”