• Prosthetic group features
• Fe₂S₂ proteins in PROMISE
• Fe₂S₂ proteins in enzyme databases
• Fe₂S₂ proteins in motif databases
• HET groups in PDB
• Fe₂S₂ proteins in 3­D databases
• References

Iron-sulphur cluster	Formal oxidation states
[Fe2S2](SCys)4	[Fe2S2]+; [Fe2S2]2+
[Fe2S2](SCys)2(NHis)2	[Fe2S2]+; [Fe2S2]2+

Iron-sulphur proteins are characterised by the presence of polymetallic systems containing sulphide ions, in which the iron ions have variable oxidation states. The simplest polymetallic system, [Fe₂S₂], is constituted by two iron ions bridged by two sulphide ions, coordinated by four cysteinyl ligands in Fe₂S₂ ferredoxins [1] or by two cysteines and two histidines in Rieske proteins [2, 3]. The oxidised proteins contain two Fe³⁺ ions, whereas the reduced proteins contain one Fe³⁺ and one Fe²⁺ ion.

Fe₂S₂ proteins in PROMISE

PROMISE ID	Description
ADRENODOXIN	Adrenodoxin­type ferredoxins (including adrenodoxin, putidaredoxin and terpredoxin)
ARHD	Aromatic­ring­hydroxylating dioxygenases
FEHASE	Iron hydrogenases
PLANTFRDX	Plant­type ferredoxins
RIESKE	Rieske iron-sulphur proteins
XANTOXIDASE	Xanthine oxidase family (including xanthine oxidase, xanthine dehydrogenase, aldehyde oxidase, CO dehydrogenase)

Fe₂S₂ proteins in enzyme databases

Enzyme cofactors		LIGAND electron transport proteins
ENZYME	LIGAND	Code	Description
Iron-sulfur	Iron Sulfur	C00138	Reduced ferredoxin
		C00139	Oxidized ferredoxin
		C00662	Reduced adrenal ferredoxin
		C00667	Oxidized adrenal ferredoxin
		C01695	Ferredoxin
		C02503	2­Iron ferredoxin

Fe₂S₂ proteins in motif databases

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
2FE2SFRDOXIN	PR00159	2FE2S_FERREDOXIN	PS00197	BL00197
ADRENODOXIN	PR00355	ADX	PS00814	BL00814
RIESKE	PR00162	RIESKE_1 RIESKE_2	PS00199 PS00200	BL00199
RNGDIOXGNASE	PR00090	RING_HYDROXYL_ALPHA	PS00570	BL00570

HET groups in PDB (at BSM)

References

1. Bertini, I., Ciurli, S. and Luchinat, C. (1995) The electronic structure of FeS centers in proteins and models. A contribution to the understanding of their electron transfer properties. Structure and Bonding 83, 1-53.
2. Mason, J.R. and Cammack, R. (1992) The electron­transport proteins of hydroxylating bacterial dioxygenases. Annu. Rev. Microbiol. 46, 277-305.
3. Cowan, J.A. (1993) Inorganic Biochemistry: An Introduction. VCH Publishers, New York.