Iron–sulfur clusters (or iron–sulphur clusters in
British spelling) 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 fr ...
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 cl ...
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 s ...
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; th ...
had many iron-sulfur clusters.
Organometallic clusters
Organometallic Fe–S clusters include the sulfido carbonyls with the formula Fe
2S
2(CO)
6, H
2Fe
3S(CO)
9, and Fe
3S
2(CO)
9. Compounds are also known that incorporate cyclopentadienyl ligands, such as (C
5H
5)
4Fe
4S
4.
Inorganic materials
center, Structure of , which features infinite chains of Fe(III) centers.">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 a ...
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 to ...
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
4S4(SR)4">e4S4(SR)4sup>2−, which are known for many R substituents, and with many cations. Variations have been prepared including the incomplete cubanes
3S4(SR)3">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 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, 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 thi ...
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.
See also
*
Bioinorganic chemistry
Bioinorganic chemistry is a field that examines the role of metals in biology. Bioinorganic chemistry includes the study of both natural phenomena such as the behavior of metalloproteins as well as artificially introduced metals, including those t ...
References
External links
{{DEFAULTSORT:Iron-sulfur cluster
Cluster chemistry
Iron compounds
Sulfur compounds