InterPro domain: IPR000825

This entry represents SufB and SufD proteins, which are homologous, and form part of the SufBCD complex in the SUF system [ 1 ]. SufB accepts sulfur transferred from SufE [ 2 ], whereas SufD may play a role in iron acquisition [ 3 ].

Iron-sulphur (FeS) clusters are important cofactors for numerous proteins involved in electron transfer, in redox and non-redox catalysis, in gene regulation, and as sensors of oxygen and iron. These functions depend on the various FeS cluster prosthetic groups, the most common being [2Fe-2S] and [4Fe-4S] [ 4 ]. FeS cluster assembly is a complex process involving the mobilisation of Fe and S atoms from storage sources, their assembly into [Fe-S] form, their transport to specific cellular locations, and their transfer to recipient apoproteins. So far, three FeS assembly machineries have been identified, which are capable of synthesising all types of [Fe-S] clusters: ISC (iron-sulphur cluster), SUF (sulphur assimilation), and NIF (nitrogen fixation) systems.

The SUF system is an alternative pathway to the ISC system that operates under iron starvation and oxidative stress. It is found in eubacteria, archaea and eukaryotes (plastids). The SUF system is encoded by the suf operon (sufABCDSE), and the six encoded proteins are arranged into two complexes (SufSE and SufBCD) and one protein (SufA). SufS is a pyridoxal-phosphate (PLP) protein displaying cysteine desulphurase activity. SufE acts as a scaffold protein that accepts S from SufS and donates it to SufA [ 5 ]. SufC is an ATPase with an unorthodox ATP-binding cassette (ABC)-like component. SufA is homologous to IscA [ 6 ], acting as a scaffold protein in which Fe and S atoms are assembled into [FeS] cluster forms, which can then easily be transferred to apoproteins targets.

1. Functional Dynamics Revealed by the Structure of the SufBCD Complex, a Novel ATP-binding Cassette (ABC) Protein That Serves as a Scaffold for Iron-Sulfur Cluster Biogenesis. J. Biol. Chem. 290, 29717-31
2. SufE transfers sulfur from SufS to SufB for iron-sulfur cluster assembly. J. Biol. Chem. 282, 13342-50
3. SufD and SufC ATPase activity are required for iron acquisition during in vivo Fe-S cluster formation on SufB. Biochemistry 49, 9402-12
4. How Escherichia coli and Saccharomyces cerevisiae build Fe/S proteins. Adv. Microb. Physiol. 50, 41-101
5. The SUF iron-sulfur cluster biosynthetic machinery: sulfur transfer from the SUFS-SUFE complex to SUFA. FEBS Lett. 581, 1362-8
6. SufA/IscA: reactivity studies of a class of scaffold proteins involved in [Fe-S] cluster assembly. J. Biol. Inorg. Chem. 9, 828-38