A proton‐NMR investigation of the fully reduced cytochrome c₇ from Desulfuromonas acetoxidans

Abstract

The solution structure via 1 H NMR of the fully reduced form of cytochrome c 7 has been obtained. The protein sample was kept reduced by addition of catalytic amounts of Desulfovibrio gigas iron hydrogenase in H 2 atmosphere after it had been checked that the presence of the hydrogenase did not affect the NMR spectrum. A final family of 35 conformers with rmsd values with respect to the mean structure of 8.7^1.5 nm and 12.4^1.3 nm for the backbone and heavy atoms, respectively, was obtained. A highly disordered loop involving residues 54±61 is present. If this loop is ignored, the rmsd values are 6.2^1.1 nm and 10.2^1.0 nm for the backbone and heavy atoms, respectively, which represent a reasonable resolution.The structure was analyzed and compared with the already available structure of the fully oxidized protein. Within the indetermination of the two solution structures, the result for the two redox forms is quite similar, confirming the special structural features of the three-heme cluster. A useful comparison can be made with the available crystal structures of cytochromes c 3 , which appear to be highly homologous except for the presence of a further heme. Finally, an analysis of the factors affecting the reduction potentials of the heme irons was performed, revealing the importance of net charges in differentiating the reduction potential when the other parameters are kept constant.

Thermodynamic and kinetic characterization of trihaem cytochrome c3 from Desulfuromonas acetoxidans

“…1), and yet this deletion does not induce any significant rearrangement of the remaining trihaem core that corresponds to haems I, III and IV of tetrahaem cytochrome c 3 [10]. The X-ray structure recently obtained [11] superposes well with the families of structures determined by NMR spectroscopy [12,13], and the geometry of the haem core, as well as the orientation of the haem ligands, closely agree with their first determination in solution from 13 C-NMR data [10]. Thus, the haem numbering that will be used throughout this article follows the structural analogy with tetrahaem cytochromes c 3 , i.e.…”

Metalloproteins Containing Cytochrome, Iron–Sulfur, or Copper Redox Centers

“…80,88,152,207−212 In some cases this class of cytochromes have up to 16 heme cofactors and display no structural similarity with other classes of cyts c . They are found as terminal electron donors in bacteria involved in sulfur metabolism.…”

The metal reductase activity of some multiheme cytochromes c : NMR structural characterization of the reduction of chromium(VI) to chromium(III) by cytochrome c 7

“…§ The three heme-containing cytochrome c 7 from the sulfurreducing bacterium Desulfuromonas acetoxidans (Cyt c 7 hereafter) has been proposed to have a role as electron-transfer protein in the sulfur metabolism of this bacterium, acting as a terminal reductase in the metabolic pathway by directly reducing elemental sulfur to sulfide (9); it has been suggested also that it could be involved in the reduction of iron(III) and manganese(IV) (10). The solution structures of the fully oxidized and fully reduced species are available, followed by the x-ray structure of the oxidized species (11)(12)(13)(14). The availability of the assigned NMR spectra and the nuclear Overhauser effects (NOEs; refs.…”