title: The reduced [2Fe-2S] clusters in adrenodoxin and Arthrospira platensis ferredoxin share spin density with protein nitrogens, probed using 2D ESEEM.
abstract: We have used X-band ESEEM to study the reduced [2Fe-2S] cluster in adrenodoxin and Arthrospira platensis ferredoxin. By use of a 2D approach (HYSCORE), we have shown that the cluster is involved in weak magnetic interactions with several nitrogens in each protein. Despite substantial differences in the shape and orientational dependence of individual cross-peaks, the major spectral features in both proteins are attributable to two peptide nitrogens (N1 and N2) with similar hyperfine couplings approximately 1.1 and approximately 0.70 MHz. The couplings determined represent a small fraction (0.0003-0.0005) of the unpaired spin density of the reduced cluster transferred to these nitrogens over H-bond bridges or the covalent bonds of cysteine ligands. Simulation of the HYSCORE spectra has allowed us to estimate the orientation of the nuclear quadrupole tensors of N1 and N2 in the g-tensor coordinate system. The most likely candidates for the role of N1 and N2 have been identified in the protein environment by comparing magnetic-resonance data with crystallographic structures of the oxidized proteins. A possible influence of redox-linked structural changes on ESEEM data is analyzed using available structures for related proteins in two redox states.
authors.affiliation: Department of Veterinary Clinical Medicine, University of Illinois, Urbana, IL 61801, USA. dikanov@illinois.edu
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Dikanov
authors.forename: Rimma I
authors.initials: RI
authors.lastname: Samoilova
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kappl
authors.forename: Antony R
authors.initials: AR
authors.lastname: Crofts
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hüttermann
mesh_terms: D000325:Adrenodoxin / Q000737:chemistry*; D000458:Cyanobacteria / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005288:Ferredoxins / Q000737:chemistry*; D006860:Hydrogen Bonding; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D000325:Adrenodoxin; D003545:Cysteine; D009584:Nitrogen