title: Comparing the electronic properties of the low-spin cyano-ferric [Fe(N4)(Cys)] active sites of superoxide reductase and p450cam using ENDOR spectroscopy and DFT calculations.
abstract: Superoxide reductase (SOR) and P450 enzymes contain similar [Fe(N)4(SCys)] active sites and, although they catalyze very different reactions, are proposed to involve analogous low-spin (hydro)peroxo-Fe(III) intermediates in their respective mechanisms that can be modeled by cyanide binding. The equatorial FeN4 ligation by four histidine ligands in CN-SOR and the heme in CN-P450cam is directly compared by 14N ENDOR, while the axial Fe-CN and Fe-S bonding is probed by 13C ENDOR of the cyanide ligand and 1Hbeta ENDOR measurements to determine the spin density delocalization onto the cysteine sulfur. There are small, but notable, differences in the bonding between Fe(III) and its ligands in the two enzymes. The ENDOR measurements are complemented by DFT computations that support the semiempirical equation used to compute spin densities on metal-coordinated cysteinyl and shed light on bonding changes as the Fe-C-N linkage bends. They further indicate that H bonds to the cysteinyl thiolate sulfur ligand reduce the spin density on the sulfur in both active sites to a degree that exceeds the difference induced by the alternative sets of "in-plane" nitrogen ligands.
authors.affiliation: Department of Chemistry and Biochemistry, Center for Metalloenzyme Studies, University of Georgia, Athens, GA 30602, USA
authors.forename: Tran-Chin
authors.initials: TC
authors.lastname: Yang
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: McNaughton
authors.forename: Michael D
authors.initials: MD
authors.lastname: Clay
authors.forename: Francis E
authors.initials: FE
authors.lastname: Jenney
authors.forename: Rangan
authors.initials: R
authors.lastname: Krishnan
authors.forename: Donald M
authors.initials: DM
authors.lastname: Kurtz
authors.forename: Michael W W
authors.initials: MW
authors.lastname: Adams
authors.forename: Michael K
authors.initials: MK
authors.lastname: Johnson
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
mesh_terms: D001665:Binding Sites; D019475:Camphor 5-Monooxygenase / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004583:Electrons; D005290:Ferric Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D010088:Oxidoreductases / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013237:Stereoisomerism
chemical_list: D005290:Ferric Compounds; D010088:Oxidoreductases; C121849:superoxide reductase; D019475:Camphor 5-Monooxygenase