Ubiquinol-cytochrome-c reductase (also known as bc1 complex or complex III) is an enzyme complex of bacterial and mitochondrial oxidative phosphorylation systems It catalyses the oxidoreduction of the mobile redox components ubiquinol and cytochrome c, generating an electrochemical potential, which is linked to ATP synthesis[1][2]. The complex consists of three subunits in most bacteria, and nine in mitochondria: both bacterial and mitochondrial complexes contain cytochrome b and cytochrome c1 subunits, and an iron-sulphur 'Rieske' subunit, which contains a high potential 2Fe-2S cluster[3].The mitochondrial form also includes six other subunits that do not possess redox centres. Plastoquinone-plastocyanin reductase (b6f complex), present in cyanobacteria and the chloroplasts of plants, catalyses the oxidoreduction of plastoquinol and cytochrome f. This complex, which is functionally similar to ubiquinol-cytochrome c reductase, comprises cytochrome b6, cytochrome f and Rieske subunits[4].
The Rieske subunit acts by binding either a ubiquinol or plastoquinol anion, transferring an electron to the 2Fe-2S cluster, then releasing the electron to the cytochrome c or cytochrome f haem iron[1][4]. The rieske domain has a [2Fe-2S] centre. Two conserved cysteines that one Fe ion while the other Fe ion is coordinated by two conserved histidines. The 2Fe-2S cluster is bound in the highly conserved C-terminal region of the Rieske subunit.
Rieske protein family
The homologues of the Rieske proteins include ISP components of cytochrome b6f complex, aromatic-ring-hydroxylating dioxygenases (phthalate dioxygenase, benzene, napthalene and toluene 1,2-dioxygenases) and arsenite oxidase (EC 1.20.98.1). Comparison of amino acid sequences has revealed the following consensus sequence:
Cys-Xaa-His-(Xaa)15–17-Cys-Xaa-Xaa-His
3D structure
The crystal structures of a number of Rieske proteins are known. The overall fold, comprising two subdomains, is dominated by antiparallel β-structure and contains the only α-helix. The smaller "cluster-binding" subdomains in mitochondrial and chloroplast proteins are virtually identical, whereas the large subdomains are substantially different in spite of a common folding topology. The [Fe2S2] cluster-binding subdomains have the topology of an incomplete antiparallel β-barrel. One iron atom of the Rieske [Fe2S2] cluster is coordinated by two cysteine residues and the other is coordinated by two histidine residues through the Nδ atoms. The ligands coordinating the cluster originate from two loops; each loop contributes one Cys and one His.
Subfamilies
Rieske iron-sulphur protein, C-terminal IPR005805
Arsenite oxidase, small subunit IPR014067
Human proteins containing this domain
AIFM3; RFESD; UQCRFS1;
References
^ ab Harnisch U, Weiss H, Sebald W (1985). "The primary structure of the iron-sulfur subunit of ubiquinol-cytochrome c reductase from Neurospora, determined by cDNA and gene sequencing". Eur. J. Biochem.149 (1): 95-99. PMID 2986972.
^ Sebald W, Gabellini N (1986). "Nucleotide sequence and transcription of the fbc operon from Rhodopseudomonas sphaeroides. Evaluation of the deduced amino acid sequences of the FeS protein, cytochrome b and cytochrome c1". Eur. J. Biochem.154 (3): 569-579. PMID 3004982.
^ Ludwig B, Kurowski B (1987). "The genes of the Paracoccus denitrificans bc1 complex. Nucleotide sequence and homologies between bacterial and mitochondrial subunits". J. Biol. Chem.262 (28): 13805-13811. PMID 2820981.
^ ab Madueno F, Napier JA, Cejudo FJ, Gray JC (1992). "Import and processing of the precursor of the Rieske FeS protein of tobacco chloroplasts". Plant Mol. Biol.20 (2): 289-299. PMID 1391772.
Further reading
Structure of a water soluble fragment of the 'Rieske' iron- sulfur protein of the bovine heart mitochondrial cytochrome bc1 complex determined by MAD phasing at 1.5 A resolution. Iwata S, Saynovits M, Link TA, Michel H Structure 1996;4:567-579. PubMed
Functional analysis in yeast of cDNA coding for the mitochondrial Rieske iron-sulfur protein of higher plants. Huang JT, Struck F, Matzinger DF, Levings CS; Proc Natl Acad Sci U S A 1991;88:10716-10720. PubMed
The mitochondrial targeting presequence of the Rieske iron-sulfur protein is processed in a single step after insertion into the cytochrome bc1 complex in mammals and retained as a subunit in the complex. Brandt U, Yu L, Yu CA, Trumpower BL; J Biol Chem 1993;268:8387-8390. PubMed
Ferraro, D.J., Gakhar, L. and Ramaswamy, S. (2005). "Rieske business: structure-function of Rieske non-heme oxygenases". Biochem. Biophys. Res. Commun.338: 175–190. PMID 16168954.
Link, T.A. (1997). "The role of the 'Rieske' iron sulfur protein in the hydroquinone oxidation (QP) site of the cytochrome bc1 complex. The 'proton-gated affinity change' mechanism". FEBS Lett.412: 257–264. PMID 9256231.
Mason, J.R. and Cammack, R. (1992). "The electron-transport proteins of hydroxylating bacterial dioxygenases". Annu. Rev. Microbiol.46: 277–305. PMID 1444257.
Rieske, J.S., Maclennan, D.H. and Coleman, R. (1964). "Isolation and properties of an iron-protein from the (reduced coenzyme Q)-cytochrome C reductase complex of the respiratory chain". Biochem. Biophys. Res. Commun.15: 338–344.
Schmidt, C.L. (2004). "Rieske iron-sulfur proteins from extremophilic organisms". J. Bioenerg. Biomembr.36: 107–113. PMID 15168614.
Schneider, D. and Schmidt, C.L. (2005). "Multiple Rieske proteins in prokaryotes: where and why?". Biochim. Biophys. Acta1710: 1–12. PMID 16271700.
Top