Rubredoxin

Abstract

Rubredoxins are small (45–55 amino acids) proteins containing a single iron ion tetrahedrally coordinated to the sulfur atoms of four cysteine residues occurring in two symmetry‐related Cys‐x‐x‐Cys‐Gly loops. The structure and redox properties of rubredoxins have been analyzed in considerable detail by X‐ray (at atomic resolution) and neutron crystallography, optical spectroscopies, NMR, various other magnetic spectroscopies, and molecular engineering. Variations of the canonical rubredoxin structure include lengthening (Cys‐x‐x‐x‐x‐Cys) or shortening (Cys–Cys) of one of the ligand loops, as well as its integration in larger proteins containing more than one metal site. Rubredoxins are found in a wide range of Archaea and Bacteria, but only exceptionally in Eukarya. They function as electron transfer agents in various redox processes, many of which remain to be fully characterized.

How the Anaerobic Enteropathogen Clostridioides difficile Tolerates Low O 2 Tensions

“…S5 A and B). We obtained values of +10 mV ± 5 mV and of −10 mV ± 5 mV for revRbr1 and revRbr2, respectively, which are similar to those of previously isolated Rds (generally in the range of −50 to +50 mV [reviewed in reference 51 ]) but significantly lower than those thus far reported for the Rd centers of the few studied canonical rubrerythrins: +213 and +281 mV for the Desulfovibrio vulgaris nigerythrin and rubrerythrin, respectively, and +185 mV for the Campylobacter jejuni desulforubrerythrin ( 43 , 47 , 52 ). Interestingly, for the enzyme from C. jejuni , the desulforedoxin-like center has a high positive potential (+240 mV) ( 47 ), compared to other known desulforedoxin-like centers (∼0 mV).…”

“…2 ), typical of S = 1/2 anti-ferro-magnetically coupled diiron sites in the mixed valence form [Fe(III)-Fe(II)]. For the revRbrs, we could only observe the typical resonances at g ≈ 4.3 and a minor resonance at g ≈ 9.3, attributable, respectively, to the middle (|±3/2>) and lower (|±1/2>) doublets of a high-spin (S = 5/2) ferric center, with a rhombicity (E/D) close to 0.33, characteristic of the ferric [Fe(SCys) 4 ] sites ( 51 ). Overall, the spectroscopic properties of FdpA and revRbrs are identical to those of analogs ( 42 – 44 ).…”

Resonance Raman spectroscopy of Fe–S proteins and their redox properties

“…Differences in the reduction potentials of Rd centers have been attributed to variations in hydrogen bonds between the cysteine sulfurs and the amide groups, and to the presence of charged residues close to the center. The larger changes in reduction potentials were obtained by mutating the cysteines to serines, resulting in a 100–200 mV decrease, which was attributed to the high electronegativity of the serinate ligand leading to a higher stabilization of the oxidized form [57, 58]. Dinuclear centers of the Rieske-type proteins (in which one of the iron ions is coordinated by two histidines, instead of the usual cysteines) have reduction potentials between − 150 and + 450 mV.…”

[FeIII(SR)4]1− complexes can be synthesized by the direct reaction of thiolates with FeCl3

“…In 1969, the protein crystal structure of oxidized rubredoxin revealed its [Fe III (S-Cys) 4 ] center [1][2][3]. The obvious route to synthetic analogs for this center involved the direct reaction of thiolate anions with a simple Fe(III) salt such as FeCl 3 .…”