Rieske Protein

Rieske proteins are iron–sulfur protein (ISP) components of cytochrome ''bc''₁ complexes and cytochrome b₆f complexes and are responsible for electron transfer in some biological systems. John S. Rieske and co-workers first discovered the protein and in 1964 isolated an acetylated form of the bovine mitochondrial protein. In 1979, Trumpower's team isolated the "oxidation factor" from bovine mitochondria and showed it was a reconstitutively-active form of the Rieske iron-sulfur protein.

It is a unique Fe-2Scluster in that one of the two Fe atoms is coordinated by two histidine residues rather than two cysteine residues. They have since been found in plants, animals, and bacteria with widely ranging electron reduction potentials from -150 to +400 mV.

Biological function

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 oxidation-reduction reaction of the mobile components ubiquinol and cytochrome c, contributing to an electrochemical potential difference across the mitochondrial inner or bacterial membrane, which is linked to ATP synthesis.

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–sulfur 'Rieske' subunit, which contains a high potential 2Fe-2S cluster. 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.

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 heme iron. The reduction of the Rieske center increases the affinity of the subunit by several orders of magnitude, stabilizing the semiquinone radical at the Q(P) site. The Rieske domain has a Fe-2Scenter. Two conserved cysteines coordinate 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 ''b''₆''f'' complex, aromatic-ring-hydroxylating dioxygenases (phthalate dioxygenase, benzene, naphthalene and toluene 1,2-dioxygenases) and arsenite oxidase ( ECbr>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 overall fold of Rieske proteins, comprising two subdomains, is dominated by antiparallel β-structure and contains variable numbers of α-helices. 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 e₂S₂cluster-binding subdomains have the topology of an incomplete antiparallel β-barrel. One iron atom of the Rieske e₂S₂cluster in the domain is coordinated by two cysteine residues and the other is coordinated by two histidine residues through the N^δ atoms. The ligands coordinating the cluster originate from two loops; each loop contributes one Cys and one His.

Subfamilies

* Rieske iron–sulfur protein, C-terminal
* Arsenite oxidase, small subunit

Human proteins containing this domain

AIFM3; RFESD; UQCRFS1;

References

Further reading

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External links

* - X-ray structure of Rieske protein (water-soluble fragment) of the bovine mitochondrial cytochrome ''bc''₁ complex
* - X-ray structure of Rieske protein (water-soluble fragment) of the spinach chloroplast cytochrome ''b''₆'' f''complex
* - X-ray structure of Rieske-type ferredoxin associated with biphenyl dioxygenase from '' Burkholderia cepacia''
* - X-ray structure of Rieske subunit of arsenite oxidase from ''Alcaligenes faecalis''
* - X-ray structure of the ''Sphingomonas yanoikuyae B1'' Rieske ferredoxin
* - X-ray structure of the Pseudomonas Naphthalene 1,2-dioxygenase Rieske ferredoxin
* {{InterPro, IPR005806 - InterPro entry for Rieske Fe-2Sregion

Iron–sulfur proteins
Protein domains
Peripheral membrane proteins
Electron-transfer proteins