title: Spectroscopic evidence for site specific chemistry at a unique iron site of the [4Fe-4S] cluster in ferredoxin:thioredoxin reductase.
abstract: Ferredoxin:thioredoxin reductase (FTR) catalyzes the reduction of the disulfide in thioredoxin in two one-electron steps using an active site comprising a [4Fe-4S] in close proximity to a redox active disulfide. Mössbauer spectroscopy has been used to investigate the ligation and electronic properties of the [4Fe-4S] cluster in as-prepared FTR which has the active-site disulfide intact and in the N-ethylmaleimide (NEM)-modified form which provides a stable analogue of the one-electron-reduced heterodisulfide intermediate and has one of the cysteines of the active-site disulfide alkylated with NEM. The results reveal novel site-specific cluster chemistry involving weak interaction of the active-site disulfide with a unique Fe site of the [4Fe-4S]2+ cluster in the resting enzyme and cleavage of the active-site disulfide with concomitant coordination of one of the cysteines to yield a [4Fe-4S]3+ cluster with a five-coordinate Fe site ligated by two cysteine residues in the NEM-modified enzyme. The results provide molecular-level insight into the catalytic mechanism of FTR and other Fe-S-cluster-containing disulfide reductases, and suggest a possible mechanism for the reductive cleavage of S-adenosylmethionine by the radical SAM family of Fe-S enzymes.
authors.affiliation: Department of Physics, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: Guy N L
authors.initials: GN
authors.lastname: Jameson
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Walters
authors.forename: Wanda
authors.initials: W
authors.lastname: Manieri
authors.forename: Peter
authors.initials: P
authors.lastname: Schürmann
authors.forename: Michael K
authors.initials: MK
authors.lastname: Johnson
authors.forename: Boi Hanh
authors.initials: BH
authors.lastname: Huynh
mesh_terms: D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D015204:Spectroscopy, Mossbauer; D018724:Spinacia oleracea / Q000201:enzymology
chemical_list: D007506:Iron-Sulfur Proteins; D010940:Plant Proteins; D010088:Oxidoreductases; C021588:ferredoxin-thioredoxin reductase