Spectroscopic evidence for site specific chemistry at a unique iron site of the [4Fe-4S] cluster in ferredoxin:thioredoxin reductase.
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.
Jameson
Guy N L
GN
Department of Physics, Emory University, Atlanta, Georgia 30322, USA.
Walters
Elizabeth M
EM
Manieri
Wanda
W
Schürmann
Peter
P
Johnson
Michael K
MK
Huynh
Boi Hanh
BH
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
D007506:Iron-Sulfur Proteins; D010940:Plant Proteins; D010088:Oxidoreductases; C021588:ferredoxin-thioredoxin reductase