NMR characterization and solution structure determination of the oxidized cytochrome c(7) from Desulfuromonas acetoxidans

The solution structure of the three-heme electron transfer protein cytochrome c(7) from Desulfuromonas acetoxidans is reported. The determination of the structure is obtained through NMR spectroscopy on the fully oxidized, paramagnetic form. The richness of structural motifs and the presence of three prosthetic groups in a protein of 68 residues is discussed in comparison with the four-heme cytochromes c(3) already characterized through x-ray crystallography. In particular, the orientation of the three hemes present in cytochrome c(7) is similar to that of three out of four hemes of cytochromes c(3). The reduction potentials of the individual hemes, which have been obtained through the sequence-specific assignment of the heme resonances, are discussed with respect to the properties of the protein matrix. This information is relevant for any attempt to understand the electron transfer pathway.