Iron–sulfur clusters (or iron–sulphur clusters in

British spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the two most notable variations being British and American ...

) are molecular ensembles of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

and

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...

. They are most often discussed in the context of the biological role for

iron–sulfur protein Iron–sulfur proteins (or iron–sulphur proteins in British spelling) are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clu ...

s, which are pervasive. Many Fe–S clusters are known in the area of

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

and as precursors to synthetic analogues of the biological clusters (see Figure). It is believed that the

last universal common ancestor The last universal common ancestor (LUCA) is the most recent population from which all organisms now living on Earth share common descent—the most recent common ancestor of all current life on Earth. This includes all cellular organisms; t ...

had many iron-sulfur clusters.

Organometallic clusters

Organometallic Fe–S clusters include the sulfido carbonyls with the formula Fe₂S₂(CO)₆, H₂Fe₃S(CO)₉, and Fe₃S₂(CO)₉. Compounds are also known that incorporate cyclopentadienyl ligands, such as (C₅H₅)₄Fe₄S₄.

Inorganic materials

center, Structure of potassium dithioferrate, which features infinite chains of Fe(III) centers.

Biological Fe–S clusters

Iron–sulfur clusters occur in many biological systems, often as components of

electron transfer Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons. Electrochemical processes ar ...

proteins. The

ferredoxin Ferredoxins (from Latin ''ferrum'': iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied t ...

proteins are the most common Fe–S clusters in nature. They feature either 2Fe–2S or 4Fe–4S centers. They occur in all branches of life. Fe–S clusters can be classified according to their Fe:S stoichiometry Fe–2S Fe–3S Fe–4S and Fe–4S The Fe–4Sclusters occur in two forms: normal ferredoxins and high potential iron proteins (HiPIP). Both adopt cuboidal structures, but they utilize different oxidation states. They are found in all forms of life. The relevant redox couple in all Fe–S proteins is Fe(II)/Fe(III). Many clusters have been synthesized in the laboratory with the formula e₄S₄(SR)₄sup>2−, which are known for many R substituents, and with many cations. Variations have been prepared including the incomplete cubanes e₃S₄(SR)₃sup>3−. The Rieske proteins contain Fe–S clusters that coordinate as a 2Fe–2S structure and can be found in the membrane bound

cytochrome bc1 Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of bi ...

complex III in the mitochondria of eukaryotes and bacteria. They are also a part of the proteins of the

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

such as the cytochrome b₆f complex in photosynthetic organisms. These photosynthetic organisms include plants, green algae, and

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

, the bacterial precursor to chloroplasts. Both are part of the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

of their respective organisms which is a crucial step in the energy harvesting for many organisms. In some instances Fe–S clusters are redox-inactive, but are proposed to have structural roles. Examples include endonuclease III and MutY.

References

External links

{{DEFAULTSORT:Iron-sulfur cluster Cluster chemistry Iron compounds Sulfur compounds

Organometallic clusters

Inorganic materials

Biological Fe–S clusters

See also

References

External links