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478  structures 3534  species 20  interactions 16897  sequences 171  architectures

Family: Rieske (PF00355)

Summary: Rieske [2Fe-2S] domain

Pfam includes annotations and additional family information from a range of different sources. These sources can be accessed via the tabs below.

This is the Wikipedia entry entitled "Coenzyme Q – cytochrome c reductase". More...

Coenzyme Q – cytochrome c reductase Edit Wikipedia article

Crystal structure of mitochondrial cytochrome bc1 complex bound with ubiquinone.[1]
Symbol UCR_TM
Pfam PF02921
InterPro IPR004192
SCOP 1be3
TCDB 3.D.3
OPM superfamily 345
OPM protein 3cx5
ubiquinol—cytochrome-c reductase
EC number
CAS number 9027-03-6
IntEnz IntEnz view
ExPASy NiceZyme view
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / QuickGO
schematic illustration of complex III reactions

The coenzyme Q : cytochrome c – oxidoreductase, sometimes called the cytochrome bc1 complex, and at other times complex III, is the third complex in the electron transport chain (EC, playing a critical role in biochemical generation of ATP (oxidative phosphorylation). Complex III is a multisubunit transmembrane protein encoded by both the mitochondrial (cytochrome b) and the nuclear genomes (all other subunits). Complex III is present in the mitochondria of all animals and all aerobic eukaryotes and the inner membranes of most eubacteria. Mutations in Complex III cause exercise intolerance as well as multisystem disorders. The bc1 complex contains 11 subunits, 3 respiratory subunits (cytochrome B, cytochrome C1, Rieske protein), 2 core proteins and 6 low-molecular weight proteins.

Ubiquinol—cytochrome-c reductase catalyzes the chemical reaction

QH2 + 2 ferricytochrome c Q + 2 ferrocytochrome c + 2 H+

Thus, the two substrates of this enzyme are quinol (QH2) and ferri- (Fe3+) cytochrome c, whereas its 3 products are quinone (Q), ferro- (Fe2+) cytochrome c, and H+.

This enzyme belongs to the family of oxidoreductases, specifically those acting on diphenols and related substances as donor with a cytochrome as acceptor. This enzyme participates in oxidative phosphorylation. It has four cofactors: cytochrome c1, cytochrome b-562, cytochrome b-566, and a 2-Iron ferredoxin of the Rieske type.


The systematic name of this enzyme class is ubiquinol:ferricytochrome-c oxidoreductase. Other names in common use include:

  • coenzyme Q-cytochrome c reductase,
  • dihydrocoenzyme Q-cytochrome c reductase,
  • reduced ubiquinone-cytochrome c reductase, complex III,
  • (mitochondrial electron transport),
  • ubiquinone-cytochrome c reductase,
  • ubiquinol-cytochrome c oxidoreductase,
  • reduced coenzyme Q-cytochrome c reductase,
  • ubiquinone-cytochrome c oxidoreductase,
  • reduced ubiquinone-cytochrome c oxidoreductase,
  • mitochondrial electron transport complex III,
  • ubiquinol-cytochrome c-2 oxidoreductase,
  • ubiquinone-cytochrome b-c1 oxidoreductase,
  • ubiquinol-cytochrome c2 reductase,
  • ubiquinol-cytochrome c1 oxidoreductase,
  • CoQH2-cytochrome c oxidoreductase,
  • ubihydroquinol:cytochrome c oxidoreductase,
  • coenzyme QH2-cytochrome c reductase, and
  • QH2:cytochrome c oxidoreductase.


Structure of complex III

Compared to the other major proton-pumping subunits of the electron transport chain, the number of subunits found can be small, as small as three polypeptide chains. This number does increase, and eleven subunits are found in higher animals.[2] Three subunits have prosthetic groups. The cytochrome b subunit has two b-type hemes (bL and bH), the cytochrome c subunit has one c-type heme (c1), and the Rieske Iron Sulfur Protein subunit (ISP) has a two iron, two sulfur iron-sulfur cluster (2Fe•2S).

Structures of complex III: PDB: 1KYO​, PDB: 1L0L

Composition of complex

In vertebrates the bc1 complex, or Complex III, contains 11 subunits: 3 respiratory subunits, 2 core proteins and 6 low-molecular weight proteins.[3][4] Proteobacterial complexes may contain as few as three subunits.[5]

Table of subunit composition of complex III

No. Subunit name Human protein Protein description from UniProt Pfam family with Human protein
Respiratory subunit proteins
1 MT-CYB / Cyt b CYB_HUMAN Cytochrome b Pfam PF13631
2 CYC1 / Cyt c1 CY1_HUMAN Cytochrome c1, heme protein, mitochondrial Pfam PF02167
3 Rieske / UCR1 UCRI_HUMAN Cytochrome b-c1 complex subunit Rieske, mitochondrial EC Pfam PF02921 , Pfam PF00355
Core protein subunits
4 QCR1 / SU1 QCR1_HUMAN Cytochrome b-c1 complex subunit 1, mitochondrial Pfam PF00675, Pfam PF05193
5 QCR2 / SU2 QCR2_HUMAN Cytochrome b-c1 complex subunit 2, mitochondrial Pfam PF00675, Pfam PF05193
Low-molecular weight protein subunits
6 QCR6 / SU6 QCR6_HUMAN Cytochrome b-c1 complex subunit 6, mitochondrial Pfam PF02320
7 QCR7 / SU7 QCR7_HUMAN Cytochrome b-c1 complex subunit 7 Pfam PF02271
8 QCR8 / SU8 QCR8_HUMAN Cytochrome b-c1 complex subunit 8 Pfam PF02939
9 QCR9 / SU9 / UCRC QCR9_HUMANa Cytochrome b-c1 complex subunit 9 Pfam PF09165
10 QCR10 / SU10 QCR10_HUMAN Cytochrome b-c1 complex subunit 10 Pfam PF05365
11 QCR11 / SU11 QCR11_HUMAN Cytochrome b-c1 complex subunit 11 Pfam PF08997
  • a In vertebrates, a cleavage product of 8 kDa from the N-terminus of the Rieske protein (Signal peptide) is retained in the complex as subunit 9. Thus subunits 10 and 11 correspond to fungal QCR9p and QCR10p.


It catalyzes the reduction of cytochrome c by oxidation of coenzyme Q (CoQ) and the concomitant pumping of 4 protons from the mitochondrial matrix to the intermembrane space:

QH2 + 2 cytochrome c (FeIII) + 2 H+
→ Q + 2 cytochrome c (FeII) + 4 H+

In the process called Q cycle,[6][7] two protons are consumed from the matrix (M), four protons are released into the inter membrane space (IM) and two electrons are passed to cytochrome c.

Reaction mechanism

The Q cycle

The reaction mechanism for complex III (cytochrome bc1, coenzyme Q: cytochrome C oxidoreductase) is known as the ubiquinone ("Q") cycle. In this cycle four protons get released into the positive "P" side (inter membrane space), but only two protons get taken up from the negative "N" side (matrix). As a result, a proton gradient is formed across the membrane. In the overall reaction, two ubiquinols are oxidized to ubiquinones and one ubiquinone is reduced to ubiquinol. In the complete mechanism, two electrons are transferred from ubiquinol to ubiquinone, via two cytochrome c intermediates.


  • 2 x QH2 oxidised to Q
  • 1 x Q reduced to QH2
  • 2 x Cyt c reduced
  • 4 x H+ released into intermembrane space
  • 2 x H+ picked up from matrix

The reaction proceeds according to the following steps:

Round 1:

  1. Cytochrome b binds a ubiquinol and a ubiquinone.
  2. The 2Fe/2S center and BL heme each pull an electron off the bound ubiquinol, releasing two hydrogens into the intermembrane space.
  3. One electron is transferred to cytochrome c1 from the 2Fe/2S centre, whilst another is transferred from the BL heme to the BH Heme.
  4. Cytochrome c1 transfers its electron to cytochrome c (not to be confused with cytochrome c1), and the BH Heme transfers its electron to a nearby ubiquinone, resulting in the formation of a ubisemiquinone.
  5. Cytochrome c diffuses. The first ubiquinol (now oxidised to ubiquinone) is released, whilst the semiquinone remains bound.

Round 2:

  1. A second ubiquinol is bound by cytochrome b.
  2. The 2Fe/2S center and BL heme each pull an electron off the bound ubiquinol, releasing two hydrogens into the intermembrane space.
  3. One electron is transferred to cytochrome c1 from the 2Fe/2S centre, whilst another is transferred from the BL heme to the BH Heme.
  4. Cytocrome c1 then transfers its electron to cytochrome c, whilst the nearby semiquinone produced from round 1 picks up a second electron from the BH heme, along with two protons from the matrix.
  5. The second ubiquinol (now oxidised to ubiquinone), along with the newly formed ubiquinol are released.[8]

Inhibitors of complex III

There are three distinct groups of Complex III inhibitors.

  • Antimycin A binds to the Qi site and inhibits the transfer of electrons in Complex III from heme bH to oxidized Q (Qi site inhibitor).
  • Myxothiazol and stigmatellin binds to the Qo site and inhibits the transfer of electrons from reduced QH2 to the Rieske Iron sulfur protein. Myxothiazol and stigmatellin bind to distinct but overlapping pockets within the Qo site.
    • Myxothiazol binds nearer to cytochrome bL (hence termed a "proximal" inhibitor).
    • Stigmatellin binds farther from heme bL and nearer the Rieske Iron sulfur protein, with which it strongly interacts.

Some have been commercialized as fungicides (the strobilurin derivatives, best known of which is azoxystrobin; QoI inhibitors) and as anti-malaria agents (atovaquone).

Also propylhexedrine inhibits cytochrome c reductase.[9]

Oxygen free radicals

A small fraction of electrons leave the electron transport chain before reaching complex IV. Premature electron leakage to oxygen results in the formation of superoxide. The relevance of this otherwise minor side reaction is that superoxide and other reactive oxygen species are highly toxic and are thought to play a role in several pathologies, as well as aging (the free radical theory of aging).[10] Electron leakage occurs mainly at the Qo site and is stimulated by antimycin A. Antimycin A locks the b hemes in the reduced state by preventing their re-oxidation at the Qi site, which, in turn, causes the steady-state concentrations of the Qo semiquinone to rise, the latter species reacting with oxygen to form superoxide. The effect of high membrane potential is thought to have a similar effect.[11] Superoxide produced at the Qo site can be released both into the mitochondrial matrix[12][13] and into the intermembrane space, where it can then reach the cytosol.[12][14] This could be explained by the fact that Complex III might produce superoxide as membrane permeable HOO rather than as membrane impermeable O−.

Human gene names

MT-CYB: mtDNA encoded cytochrome b; mutations associated with exercise intolerance

CYC1:cytochrome c1

CYCS: cytochrome c

UQCRFS1: Rieske iron sulfur protein

UQCRB: Ubiquinone binding protein, mutation linked with mitochondrial complex III deficiency nuclear type 3

UQCRH: hinge protein

UQCRC2: Core 2, mutations linked to mitochondrial complex III deficiency, nuclear type 5

UQCRC1: Core 1

UQCR: 6.4KD subunit

UQCR10: 7.2KD subunit

TTC19: Newly identified subunit, mutations linked to complex III deficiency nuclear type 2

Mutations in complex III genes in human disease

Mutations in complex III-related genes typically manifest as exercise intolerance.[15][16] Other mutations have been reported to cause septo-optic dysplasia[17] and multisystem disorders.[18] However, mutations in BCS1L, a gene responsible for proper maturation of complex III, can result in Björnstad syndrome and the GRACILE syndrome, which in neonates are lethal conditions that have multisystem and neurologic manifestations typifying severe mitochondrial disorders. The pathogenicity of several mutations has been verified in model systems such as yeast.[19]

The extent to which these various pathologies are due to bioenergetic deficits or overproduction of superoxide is presently unknown.

See also

Additional images


  1. ^ PDB: 1ntz​; Gao X, Wen X, Esser L, Quinn B, Yu L, Yu CA, Xia D (August 2003). "Structural basis for the quinone reduction in the bc1 complex: a comparative analysis of crystal structures of mitochondrial cytochrome bc1 with bound substrate and inhibitors at the Qi site". Biochemistry. 42 (30): 9067–80. doi:10.1021/bi0341814. PMID 12885240. 
  2. ^ Iwata S, Lee JW, Okada K, Lee JK, Iwata M, Rasmussen B, Link TA, Ramaswamy S, Jap BK (July 1998). "Complete structure of the 11-subunit bovine mitochondrial cytochrome bc1 complex". Science. 281 (5373): 64–71. doi:10.1126/science.281.5373.64. PMID 9651245. 
  3. ^ Zhang Z, Huang L, Shulmeister VM, Chi YI, Kim KK, Hung LW, et al. (1998). "Electron transfer by domain movement in cytochrome bc1". Nature. 392 (6677): 677–84. doi:10.1038/33612. PMID 9565029. 
  4. ^ Hao GF, Wang F, Li H, Zhu XL, Yang WC, Huang LS, et al. (2012). "Computational discovery of picomolar Q(o) site inhibitors of cytochrome bc1 complex". J Am Chem Soc. 134 (27): 11168–76. doi:10.1021/ja3001908. PMID 22690928. 
  5. ^ Yang XH, Trumpower BL (1986). "Purification of a three-subunit ubiquinol-cytochrome c oxidoreductase complex from Paracoccus denitrificans". J Biol Chem. 261: 12282–9. PMID 3017970. 
  6. ^ Kramer DM, Roberts AG, Muller F, Cape J, Bowman MK (2004). "Q-cycle bypass reactions at the Qo site of the cytochrome bc1 (and related) complexes". Meth. Enzymol. Methods in Enzymology. 382: 21–45. doi:10.1016/S0076-6879(04)82002-0. ISBN 978-0-12-182786-1. PMID 15047094. 
  7. ^ Crofts AR (2004). "The cytochrome bc1 complex: function in the context of structure". Annu. Rev. Physiol. 66: 689–733. doi:10.1146/annurev.physiol.66.032102.150251. PMID 14977419. 
  8. ^ Ferguson SJ, Nicholls D, Ferguson S (2002). Bioenergetics (3rd ed.). San Diego: Academic. pp. 114–117. ISBN 0-12-518121-3. 
  9. ^ Holmes, J. H.; Sapeika, N; Zwarenstein, H (1975). "Inhibitory effect of anti-obesity drugs on NADH dehydrogenase of mouse heart homogenates". Research communications in chemical pathology and pharmacology. 11 (4): 645–6. PMID 241101. 
  10. ^ Muller, F. L.; Lustgarten, M. S.; Jang, Y.; Richardson, A. & Van Remmen, H. (2007). "Trends in oxidative aging theories". Free Radic. Biol. Med. 43 (4): 477–503. doi:10.1016/j.freeradbiomed.2007.03.034. PMID 17640558. 
  11. ^ Skulachev VP (May 1996). "Role of uncoupled and non-coupled oxidations in maintenance of safely low levels of oxygen and its one-electron reductants". Q. Rev. Biophys. 29 (2): 169–202. doi:10.1017/s0033583500005795. PMID 8870073. 
  12. ^ a b Muller F (2000). "The nature and mechanism of superoxide production by the electron transport chain: Its relevance to aging". AGE. 23 (4): 227–253. doi:10.1007/s11357-000-0022-9. PMC 3455268Freely accessible. PMID 23604868. 
  13. ^ a b Muller FL, Liu Y, Van Remmen H (November 2004). "Complex III releases superoxide to both sides of the inner mitochondrial membrane". J. Biol. Chem. 279 (47): 49064–73. doi:10.1074/jbc.M407715200. PMID 15317809. 
  14. ^ Han D, Williams E, Cadenas E (January 2001). "Mitochondrial respiratory chain-dependent generation of superoxide anion and its release into the intermembrane space". Biochem. J. 353 (Pt 2): 411–6. doi:10.1042/0264-6021:3530411. PMC 1221585Freely accessible. PMID 11139407. 
  15. ^ DiMauro S (November 2006). "Mitochondrial myopathies" (PDF). Curr Opin Rheumatol. 18 (6): 636–41. doi:10.1097/01.bor.0000245729.17759.f2. PMID 17053512. 
  16. ^ DiMauro S (June 2007). "Mitochondrial DNA medicine". Biosci. Rep. 27 (1–3): 5–9. doi:10.1007/s10540-007-9032-5. PMID 17484047. 
  17. ^ Schuelke M, Krude H, Finckh B, Mayatepek E, Janssen A, Schmelz M, Trefz F, Trijbels F, Smeitink J (March 2002). "Septo-optic dysplasia associated with a new mitochondrial cytochrome b mutation". Ann. Neurol. 51 (3): 388–92. doi:10.1002/ana.10151. PMID 11891837. 
  18. ^ Wibrand F, Ravn K, Schwartz M, Rosenberg T, Horn N, Vissing J (October 2001). "Multisystem disorder associated with a missense mutation in the mitochondrial cytochrome b gene". Ann. Neurol. 50 (4): 540–3. doi:10.1002/ana.1224. PMID 11601507. 
  19. ^ Fisher N, Castleden CK, Bourges I, Brasseur G, Dujardin G, Meunier B (March 2004). "Human disease-related mutations in cytochrome b studied in yeast". J. Biol. Chem. 279 (13): 12951–8. doi:10.1074/jbc.M313866200. PMID 14718526. 

Further reading

External links

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This is the Wikipedia entry entitled "Rieske protein". More...

Rieske protein Edit Wikipedia article

1VF5 1.jpg
Rieske protein from cytochrome b6f complex. (PDB: 1vf5​)
Symbol Rieske
Pfam PF00355
InterPro IPR005806
SCOP 1rie
TCDB 3.E.2
OPM protein 1q90
Cytochrome B6-F complex Fe-S subunit, alpha helical transmembrane domain
PDB 1vf5 EBI.jpg
crystal structure of cytochrome b6f complex from m.laminosus
Symbol CytB6-F_Fe-S
Pfam PF08802
InterPro IPR014909

Rieske proteins are iron-sulfur protein (ISP) components of cytochrome bc1 complexes and cytochrome b6f complexes and responsible for electron transfer in some biological systems. John S. Rieske and co-workers first discovered and isolated the proteins in 1964.[1] It is a unique [2Fe-2S] cluster 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.[2]

Biological function (in oxidative phosphorylation systems)

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.[3][4]

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.[5] 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.[6]

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.[3][6] 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.[7] The Rieske domain has a [2Fe-2S] center. 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 b6f complex, aromatic-ring-hydroxylating dioxygenases (phthalate dioxygenase, benzene, naphthalene and toluene 1,2-dioxygenases) and arsenite oxidase (EC Comparison of amino acid sequences has revealed the following consensus sequence:

Rieske iron-sulfur center

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 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 [Fe2S2] cluster-binding subdomains have the topology of an incomplete antiparallel β-barrel. One iron atom of the Rieske [Fe2S2] cluster in the domain 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.


Human proteins containing this domain



  1. ^ Rieske JS, Maclennan DH, 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 (4): 338–344. doi:10.1016/0006-291X(64)90171-8. 
  2. ^ Brown, E.N. and Friemann, R. and Karlsson, A. and Parales, J.V. and Couture, M.M. and Eltis, L.D. and Ramaswamy, S. (2008). "Determining Rieske cluster reduction potentials". J.Biol.Inorg.Chem. 13 (8): 1301–1313. doi:10.1007/s00775-008-0413-4. PMID 18719951. 
  3. ^ a b Harnisch U, Weiss H, Sebald W (May 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): 95–9. doi:10.1111/j.1432-1033.1985.tb08898.x. PMID 2986972. 
  4. ^ Gabellini N, Sebald W (February 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): 569–79. doi:10.1111/j.1432-1033.1986.tb09437.x. PMID 3004982. 
  5. ^ Kurowski B, Ludwig B (October 1987). "The genes of the Paracoccus denitrificans bc1 complex. Nucleotide sequence and homologies between bacterial and mitochondrial subunits". J. Biol. Chem. 262 (28): 13805–11. PMID 2820981. 
  6. ^ a b Madueño F, Napier JA, Cejudo FJ, Gray JC (October 1992). "Import and processing of the precursor of the Rieske FeS protein of tobacco chloroplasts". Plant Mol. Biol. 20 (2): 289–99. doi:10.1007/BF00014496. PMID 1391772. 
  7. ^ Link TA (July 1997). "The role of the 'Rieske' iron sulfur protein in the hydroquinone oxidation (Q(P)) site of the cytochrome bc1 complex. The 'proton-gated affinity change' mechanism". FEBS Lett. 412 (2): 257–64. doi:10.1016/S0014-5793(97)00772-2. PMID 9256231. 

Further reading

External links

  • PDB: 1RIE​ - X-ray structure of Rieske protein (water-soluble fragment) of the bovine mitochondrial cytochrome bc1 complex
  • PDB: 1RFS​ - X-ray structure of Rieske protein (water-soluble fragment) of the spinach chloroplast cytochrome b6 fcomplex
  • PDB: 1FQT​ - X-ray structure of Rieske-type ferredoxin associated with biphenyl dioxygenase from Burkholderia cepacia
  • PDB: 1G8J​ - X-ray structure of Rieske subunit of arsenite oxidase from Alcaligenes faecalis
  • PDB: 2I7F​ - X-ray structure of the Sphingomonas yanoikuyae B1 Rieske ferredoxin
  • PDB: 2QPZ​ - X-ray structure of the Pseudomonas Naphthalene 1,2-dioxygenase Rieske ferredoxin
  • InterPro: IPR005806 - InterPro entry for Rieske [2Fe-2S] region

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Rieske [2Fe-2S] domain Provide feedback

The rieske domain has a [2Fe-2S] centre. Two conserved cysteines coordinate one Fe ion, while the other Fe ion is coordinated by two conserved histidines. In hyperthermophilic archaea there is a SKTPCX(2-3)C motif at the C-terminus. The cysteines in this motif form a disulphide bridge, which stabilises the protein [4].

Literature references

  1. Iwata S, Saynovits M, Link TA, Michel H , Structure 1996;4:567-579.: 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. PUBMED:8736555 EPMC:8736555

  2. Huang JT, Struck F, Matzinger DF, Levings CS; , Proc Natl Acad Sci U S A 1991;88:10716-10720.: Functional analysis in yeast of cDNA coding for the mitochondrial Rieske iron-sulfur protein of higher plants. PUBMED:1961737 EPMC:1961737

  3. Brandt U, Yu L, Yu CA, Trumpower BL; , J Biol Chem 1993;268:8387-8390.: 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. PUBMED:8386158 EPMC:8386158

  4. Botelho HM, Leal SS, Veith A, Prosinecki V, Bauer C, Frohlich R, Kletzin A, Gomes CM;, J Biol Inorg Chem. 2010;15:271-281.: Role of a novel disulfide bridge within the all-beta fold of soluble Rieske proteins. PUBMED:19862563 EPMC:19862563

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR017941

There are multiple types of iron-sulphur clusters which are grouped into three main categories based on their atomic content: [2Fe-2S], [3Fe-4S], [4Fe-4S] (see PROSITEDOC), and other hybrid or mixed metal types. Two general types of [2Fe-2S] clusters are known and they differ in their coordinating residues. The ferredoxin-type [2Fe-2S] clusters are coordinated to the protein by four cysteine residues (see PROSITEDOC). The Rieske-type [2Fe-2S] cluster is coordinated to its protein by two cysteine residues and two histidine residues [PUBMED:16168954, PUBMED:16271700].

The structure of several Rieske domains has been solved [PUBMED:8736555]. It contains three layers of antiparallel beta sheets forming two beta sandwiches. Both beta sandwiches share the central sheet 2. The metal-binding site is at the top of the beta sandwich formed by the sheets 2 and 3. The Fe1 iron of the Rieske cluster is coordinated by two cysteines while the other iron Fe2 is coordinated by two histidines. Two inorganic sulphide ions bridge the two iron ions forming a flat, rhombic cluster.

Rieske-type iron-sulphur clusters are common to electron transfer chains of mitochondria and chloroplast and to non-haem iron oxygenase systems:

  • The Rieske protein of the Ubiquinol-cytochrome c reductase (EC) (also known as the bc1 complex or complex III), a complex of the electron transport chains of mitochondria and of some aerobic prokaryotes; it catalyses the oxidoreduction of ubiquinol and cytochrome c.
  • The Rieske protein of chloroplastic plastoquinone-plastocyanin reductase (EC) (also known as the b6f complex). It is functionally similar to the bc1 complex and catalyses the oxidoreduction of plastoquinol and cytochrome f.
  • Bacterial naphthalene 1,2-dioxygenase subunit alpha, a component of the naphthalene dioxygenase (NDO) multicomponent enzyme system which catalyses the incorporation of both atoms of molecular oxygen into naphthalene to form cis-naphthalene dihydrodiol.
  • Bacterial 3-phenylpropionate dioxygenase ferredoxin subunit.
  • Bacterial toluene monoxygenase.
  • Bacterial biphenyl dioxygenase.

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan ISP-domain (CL0516), which has the following description:

This superfamily is characterised by Rieske Iron-sulfur families of the [2Fe-2S] type including NADH-nitrite reductase small subunit NirD proteins. This domain has an all-beta rubredoxin-like fold.

The clan contains the following 2 members:

Rieske Rieske_2


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You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

HMM logo

HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...


This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.

Note: You can also download the data file for the tree.

Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

Curation View help on the curation process

Seed source: Prosite & Pfam-B_31 (release 4.1)
Previous IDs: none
Type: Domain
Author: Finn RD, Griffiths-Jones SR, Eberhardt R
Number in seed: 55
Number in full: 16897
Average length of the domain: 95.30 aa
Average identity of full alignment: 20 %
Average coverage of the sequence by the domain: 29.33 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 26740544 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.3 20.3
Trusted cut-off 20.3 20.3
Noise cut-off 20.2 20.2
Model length: 89
Family (HMM) version: 25
Download: download the raw HMM for this family

Species distribution

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Colour assignments

Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the adjacent tab. More...

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Tree controls


The tree shows the occurrence of this domain across different species. More...


Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.


There are 20 interactions for this family. More...

Pyr_redox_2 Ring_hydroxyl_B Reductase_C Cytochrom_B_N_2 Ring_hydroxyl_B Cytochrom_C1 V-set Aromatic_hydrox Cytochrom_C1 Molydop_binding Cytochrom_B_N_2 Ring_hydroxyl_A Cytochrom_B_C CytB6-F_Fe-S Molybdopterin Cytochrom_B_C Aromatic_hydrox UCR_hinge Ring_hydroxyl_A Rieske


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Rieske domain has been found. There are 478 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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