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.

Isolation and Characterization of the Small Subunit of the Uptake Hydrogenase from the Cyanobacterium Nostoc punctiforme

“…The protein presents two discernible absorption bands in the 300 -500-nm region with maxima at ϳ340 and 420 nm, respectively, as well as a broad shoulder in the 500 -600-nm region. The shape and location of these bands are typical of broad ligand-to-metal charge transfer in iron-sulfur proteins such as ferredoxins (29,30) and indicated that iron-sulfur clusters had been successfully incorporated into f-HupS. This is further substantiated by the 420/315 nm absorbance ratio of 0.43, which is comparable with the corresponding ratio 0.68 found in ferredoxin II from Desulfovibrio gigas (29).…”

The crystal structure of FdxA, a 7Fe ferredoxin from Mycobacterium smegmatis

“…Interestingly, such selective conversion of cluster II does not destabilize cluster I, nor has sizeable effects on the overall protein structure [21,22]. It must additionally be recalled that in 7Fe Fds the redox functional role has been assigned to the [3Fe-4S] cluster I, whereas cluster II is believed to play only a structural function [23] [24].…”