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 redox reaction between CrO(4)(2-) and the fully reduced three-heme cytochrome c(7) from Desulfuromonas acetoxidans to give chromium(III) and the fully oxidized protein has been followed by NMR spectroscopy. The hyperfine coupling between the oxidized protein protons and chromium(III), which remains bound to the protein, gives rise to line-broadening effects on the NMR resonances that can be transformed into proton-metal distance restraints. Structure calculations based on these unconventional constraints allowed us to demonstrate that chromium(III) binds at a unique site and to locate it on the protein surface. The metal ion is located 7.9 +/- 0.4 A from the iron of heme IV, 16.3 +/- 0.7 A from the iron of heme III, and 22.5 +/- 0.5 A from the iron of heme I. Shift changes caused by the presence of unreactive MoO(4)(2-), a CrO(4)(2-) analogue, indicate the involvement of the same protein area in the anion binding. The titration of the oxidation of cytochrome c(7) shows a detailed mechanism of action. The presence of a specific binding site supports the hypothesis of the biological role of this cytochrome as a metal reductase.
Magnetic Resonance Center and Department of Chemistry, University of Florence, Via Luigi Sacconi, 6, 50019 Sesto Fiorentino (Florence), Italy.
Michael
M
Assfalg
Ivano
I
Bertini
Mireille
M
Bruschi
Caroline
C
Michel
Paola
P
Turano
D001665:Binding Sites; D002857:Chromium / Q000737:chemistry*; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D020564:Deltaproteobacteria / Q000201:enzymology*; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation
D003574:Cytochrome c Group; D006420:Hemeproteins; D008667:Metalloproteins; C114913:cytochrome C7; D002857:Chromium; C074702:chromium hexavalent ion; D006418:Heme