There are multiple types of iron-sulfur clusters which are grouped into three main categories based on their atomic content: [2Fe-2S], [3Fe-4S], [4Fe-4S] (see <PDOC00176>), 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 <PDOC00175>). The Rieske-type [2Fe-2S] cluster is coordinated to its protein by two cysteine residues and two histidine residues [1,2].

The structure of several Rieske domains has been solved (see for example <PDB:1RIE>) [3]. It contains three layers of antiparallel β sheets forming two β sandwiches. Both β sandwiches share the central sheet 2. The metal-binding site is at the top of the β 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 sulfide ions bridge the two iron ions forming a flat, rhombic cluster.

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

• The Rieske protein of the Ubiquinol-cytochrome c reductase (EC 1.10.2.2) (also known as the bc1 complex or complex III), a complex of the electron transport chains of mitochondria and of some aerobic prokaryotes; it catalyzes the oxidoreduction of ubiquinol and cytochrome c.
• The Rieske protein of chloroplastic plastoquinone-plastocyanin reductase (EC 1.10.99.1) (also known as the b6f complex). It is functionally similar to the bc1 complex and catalyzes the oxidoreduction of plastoquinol and cytochrome f.
• Bacterial naphthalene 1,2-dioxygenase subunit α, a component of the naphthalene dioxygenase (NDO) multicomponent enzyme system which catalyzes 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.

The profile we developed covers the whole Rieske domain.