Iron-sulfur cluster

An iron-sulfur cluster is a structural motif found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase and Coenzyme Q - cytochrome c reductase, and nitrogenase. Usually the term iron-sulfur cluster refers species within Iron-sulfur proteins that contain only iron and sulfur, and three distinct kinds are well known:
 * The 2 iron, 2 sulfur cluster, consisting of two iron atoms, with two inorganic sulfur atoms found between the irons and acting as bridging ligands. The irons themselves are usually coordinated to the sulfurs of 4 cysteine side chains. In the related Rieske proteins, a pair of cysteinyl residues on one iron center are replaced by 2 imidazole ligands from the side chain of two histidine residues.  These species exist in two oxidation states, (FeIII)2 and FeIIIFeII.
 * The 4 iron, 4 sulfur cluster, consisting of 4 irons, with 4 inorganic sulfur atoms found between the irons and acting as bridging ligands. The irons, once again, are coordinated to the protein via the sulfurs of 4 cysteine side chains. These species exist in two oxidation states, (FeIII)2(FeII)2 and either (FeIII)3(FeII)1 or (FeIII)1(FeII)3.
 * The 3 iron, 4 sulfur cluster, which is a 4 iron, 4 sulfur cluster with one missing iron atom.

Function
Iron-sulfur clusters are best know for their role in oxidation-reduction reactions. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally some Fe-S proteins regulate gene expression. Fe-S proteins are vulnerable to attack by biogenic nitric oxide.

Biosynthesis
The biosynthesis of the Fe-S clusters has been well studied.

Synthetic analogues
Synthetic analogues of the naturally occuring Fe-S clusters were first reported by Holm and coworkers. Treatment of iron salts with a mixture of thiolates and sulfide affords derivatives such as (Et4N)2Fe4S4(SCH2Ph)4].

External link

 * Examples of iron-sulfur clusters

Cluster ferro-zolfo