Iron–sulfur cluster biosynthesis

In biochemistry, the iron–sulfur cluster biosynthesis describes the components and processes involved in the biosynthesis of iron–sulfur proteins. The topic is of interest because these proteins are pervasive. The iron sulfur proteins contain iron–sulfur clusters, some with elaborate structures, that feature iron and sulfide centers. One broad biosynthetic task is producing sulfide (S^2-), which requires various families of enzymes. Another broad task is affixing the sulfide to iron, which is achieved on scaffolds, which are nonfunctional. Finally these Fe-S cluster is transferred to a target protein, which then become functional.^[1]

Fe-S_biosyn
e.coli isca crystal structure to 2.3 a
Identifiers
Symbol	Fe-S_biosyn
Pfam	PF01521
InterPro	IPR000361
PROSITE	PDOC00887
SCOP2	1nwb / SCOPe / SUPFAM
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

The formation of iron–sulfur clusters are produced by one of four pathways:^[2]

• Nitrogen fixation (NIF) system, which is also found in bacteria that are not nitrogen-fixing.^[3]
• Iron–sulfur cluster (ISC) system, in bacterial and mitochondria
• Sulfur assimilation (SUF) system, in plastids and some bacteria

In addition to those three systems, the so-called Cystosolic Iron–sulfur Assembly (CIA) is invoked for cytosolic and nuclear Fe–S proteins.

Mechanisms

The assembly of iron–sulfur clusters cluster begins with the production of the equivalent of a sulfur (sulfur atoms per se are not found in nature). The required sulfur atom is obtained from free cysteine by the action of so-called cysteine desulfurases. One prominent desulfurase is called IscS, a pyridoxal phosphate-dependent enzyme. The sulfur atom from the cysteine substrate is transferred to residue Cys-328 of IscS, forming a persulfide:

L-cysteine + [enzyme]-cysteine ${\displaystyle \rightleftharpoons }$  L-alanine + [enzyme]-S-sulfanylcysteine

The persulfide functional group R-S-S-H functions as a source of "inorganic sulfur" that will be incorporated into Fe-S clusters. Subsequently, IscS transfers this "extra" sulfur to IscU.^[4] In addition to IscS and IscU, bacterial Fe-S assembly requires IscA, an 11 kDa protein of uncertain function.^[5]

The Suf system for iron–sulfur cluster biosynthesis is generally similar to the Isc system (and the Nif system). The analogy extends to the existence of SufA, SufS, and SufU. The Suf system operates with fewer chaperones.^[1]

References

1. Johnson DC, Dean DR, Smith AD, Johnson MK (2005). "Structure, function, and formation of biological iron–sulfur clusters". Annual Review of Biochemistry. 74: 247–81. doi:10.1146/annurev.biochem.74.082803.133518. PMID 15952888.
2. Lill R (August 2009). "Function and biogenesis of iron-sulphur proteins". Nature. 460 (7257): 831–8. Bibcode:2009Natur.460..831L. doi:10.1038/nature08301. PMID 19675643. S2CID 205217943.
3. Santos PC, Dean DR (2017). "FeS Cluster Assembly: NIF System in Nitrogen-Fixing Bacteria". Encyclopedia of Inorganic and Bioinorganic Chemistry. pp. 1–13. doi:10.1002/9781119951438.eibc2466. ISBN 978-1-119-95143-8.
4. Kato S, Mihara H, Kurihara T, Takahashi Y, Tokumoto U, Yoshimura T, Esaki N (April 2002). "Cys-328 of IscS and Cys-63 of IscU are the sites of disulfide bridge formation in a covalently bound IscS/IscU complex: implications for the mechanism of iron–sulfur cluster assembly". Proceedings of the National Academy of Sciences of the United States of America. 99 (9): 5948–52. Bibcode:2002PNAS...99.5948K. doi:10.1073/pnas.082123599. PMC 122882. PMID 11972033.
5. Cupp-Vickery JR, Silberg JJ, Ta DT, Vickery LE (April 2004). "Crystal structure of IscA, an iron–sulfur cluster assembly protein from Escherichia coli". Journal of Molecular Biology. 338 (1): 127–37. doi:10.1016/j.jmb.2004.02.027. PMID 15050828.

This article incorporates text from the public domain Pfam and InterPro: IPR000361