Iron protein domain structure

This group of proteins is ubiquitous. Most of the iron-sulfur proteins transfer electrons at negative redox potentials, e.g. in the respiratory chain or in photosynthesis, but some possess enzymatic, sensing or regulatory activity and they can also be involved in stabilization of protein domain structures or in radical formation. The important role of the element combination iron and sulfur in biology derives from many factors including availability, solubility and reactivity. The role of the sulfur ligands has been reviewed recently. For more reviews of various EPR-related aspects the reader is referred to the earlier report in this series. 

Fig. 105. Examples of small disulfide-rich or metal-rich proteins (shown on the right side) compared with their more regular counterparts in other structural categories (shown at the left), (a) Tobacco mosaic virus protein, an up-and-down helix bundle (b) cytochrome bs, a distorted up-and-down helix bundle (c) trypsin domain 1, a Greek key antiparallel /3 barrel (d) high-potential iron protein, a distorted Greek key /3 barrel (e) glutathione reductase domain 3, an open-face sandwich fi sheet (f) ferredoxin, a distorted open-face sandwich f) sheet.

Three other proteins with similar domain structure as that of FprA were reported in other bacteria (WasserfaUen et al. 1995 Gomes et al. 1997, 2000). The recombinant CthFprA and CthHrb, overexpressed in E. coli, were purified and characterized. Both FprA and Hrb were found to be present as dimers. Metal/cofactor analysis of the purified proteins revealed the presence of 2 mol each of iron and flavin (FMN) per mole dimer of Hrb and 4 mol of iron and 2 mol FMN per mole dimer of FprA. The EPR spectra of the purified proteins indicated that iron is present in a di-iron center in FprA and as a Fe(Cys)4 cluster in Hrb. 

Type 1 copper proteins are the class of proteins for which cupredoxins were originally named. Type 1 copper proteins include both proteins with known electron transfer function (e.g., plastocyanin and rusticyanin), and proteins whose biological functions have not been determined conclusively (e.g., stellacyanin and plantacyanin). Although these proteins with unknown function cannot be called cupredoxins by the strict functional definition, they have been classified as cupredoxins because they share the same overall structural fold and metal-binding sites as cupredoxins. In addition, many multidomain proteins, such as laccase, ascorbate oxidase, and ceruloplasmin, contain multiple metal centers, one of which is a type 1 copper. Those cupredoxin centers are also included here. Finally, both the Cua center in cytochrome c oxidase (CcO) and nitrous oxide reductase (N2OR), and the red copper center in nitrocyanin will be discussed in this chapter because their metal centers are structurally related to the type 1 copper center and the protein domain that contains both centers share the same overall structural motif as those of cupredoxins. The Cua center also functions as an electron transfer agent. Like ferredoxins, which contain either dinuclear or tetranuclear iron-sulfur centers, cupredoxins may include either the mononuclear or the dinuclear copper center in their metal-binding sites. 

They are highly helical and have nearly identical foldings. The monomer is a two domain structure with six major helical segments and three strands of antiparallel P-sheet . The iron is ligated to four protein side chains, one from each of the two crossing helices in the N-terminal domain and the third and fourth from residues... 

Molecular Structures That Show Relocation of the Globular Domain of the Rieske Iron Protein... 

Fig. 8. (a) Structure of the full-length Rieske protein from bovine heart mitochondrial bci complex. The catalytic domain is connected to the transmembrane helix by a flexible linker, (b) Superposition of the three positional states of the catalytic domain of the Rieske protein observed in different crystal forms. The ci state is shown in white, the intermediate state in gray, and the b state in black. Cytochrome b consists of eight transmembrane helices and contains two heme centers, heme and Sh-Cytochrome c i has a water-soluble catalytic domain containing heme c i and is anchored by a C-terminal transmembrane helix. The heme groups are shown as wireframes, the iron atoms as well as the Rieske cluster in the three states as space-filling representations. 

Several /i-solenoid domains appear to promote the oligomerization of multidomain proteins. There are at least three types of /i-solenoid association. First, oligomers (dimers or trimers) are formed by lateral interaction of the solenoids. For example, the C-terminal domain of the bacterial cell division inhibitor MinC is a short right-handed T-type solenoid with an apolar lateral face that mediates homodimerization (Cordell et al., 2001). Trimers of several bacterial transferases are formed by lateral, in-register, interaction of left-handed T-type /1-solenoids (Fig. 5). Second, dimers may form via interactions of the open terminal coils of /1-solenoids as in the dimeric structure of iron transporter stabilizer SufD (Badger et al., 2005). Finally, dimerization may be mediated by swapping of /1-strands of the terminal coils, as in the CAP (Dodatko et al., 2004) (Fig. S). 

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