Ferredoxins Containing Two DifferentFe/SCenters of the Forms [4Fe–4S] and [3Fe–4S]

Abstract

This article reviews 7Fe ferredoxins (Fds), [FeS] proteins that contain [3Fe–4S] +/0 and [4Fe–4S] 2+/+ clusters. The 7Fe Fds from 19 prokaryotes are described in terms of biological function, and categorized with respect to cysteine ligand motifs, length of amino‐acid sequence, and metal ion content. Biochemical, mutagenesis, electrochemical, spectroscopic, and crystallographic data are summarized for well‐studied examples of distinct subclasses, including 7Fe Fds from Azotobacter vinelandii , Desulfovibrio africanus , Bacillus schlegelii , and Sulfolobus acidocaldarius . 7Fe Fds have been used to study cysteine ligand motifs, the interconversion of [3Fe–4S] and [4Fe–4S] clusters, proton transfer to [3Fe–4S] 0 clusters, and the protein control of [FeS] cluster reduction potential.

Structural diffusion properties of two atypical Dps from the cyanobacterium Nostoc punctiforme disclose interactions with ferredoxins and DNA

“…S6b, middle panel). These spectral characteristics arise from ligand-to-metal charge transfer bands that are typical for [2Fe-2S] centers in the oxidized state[57]. In contrast, NpFdx9presented broader absorption bands around the 320 and 420 nm region characteristic of proteins iron-sulfur centers were [4Fe-4S] centers, with a minor population (~20%) being [3Fe-4S] centers.…”

Electron Transport to Nitrogenase: Diverse Routes for a Common Destination

“…They can be divided into several groups depending on the number and types of iron-sulfur cluster(s), e.g., [2Fe-2S], [4Fe-4S], [3Fe-4S], 2[4Fe-4S] and [3Fe-4S][4Fe-4S] Fds are known (Matsubara and Saeki, 1992;Otaka and Ooi, 1989). Among these, the significant electron donors to the Fe protein may be limited to the [2Fe-2S] and 2[4Fe-4S] groups (Fukuyama, 2001;Sieker and Adman, 2001;Stout, 2001;Zanetti et al, 2001). The redox potentials of Fds are modulated by their polypeptide structure and occur in the ranges of -240 to -460 mV, -50 to -420 mV and 0 to -645 mV, respectively, for the couples [2Fe-2S] 2+/1+ , [3Fe-4S] 1+/0 and [4Fe-4S] 2+/1+ (Cammack, 1992).…”

“…Three-dimensional structures of a number of Fds are available, including several from diazotrophs, such as the [2Fe-2S]-type from Anabaena sp. PCC 7120, the 2[4Fe-4S]-type from C. pasteurianum, and the [3Fe-4S][4Fe-4S]-type from A. vinelandii, along with their mutant forms (see references in Sieker and Adman, 2001;Stout, 2001;Zanetti et al, 2001). The Fe-S clusters are covalently bound through cysteinyl (Cys) residues, which display characteristic spacing (Figure 1), the so-called "cluster-binding motifs" (Bruschi and Guerlesquin, 1988;Cammack, 1992;Matsubara and Saeki, 1992).…”