title: (57)Fe ENDOR spectroscopy on the iron-sulfur cluster involved in substrate reduction of heterodisulfide reductase.
abstract: Heterodisulfide reductase (Hdr) from methanogenic archea is an iron-sulfur protein that catalyzes the reversible two-electron reduction of the mixed disulfide CoM-S-S-CoB to the thiol coenzymes, coenzyme M (CoM-SH) and coenzyme B (CoB-SH). It is unusual that this enzyme uses an iron-sulfur cluster to mediate disulfide reduction in two one-electron steps via site-specific cluster chemistry. Upon half-reaction of the oxidized enzyme with CoM-SH in the absence of CoB-SH, an iron-based paramagnetic intermediate is formed, designated CoM-Hdr. In this Communication we report 57Fe pulsed ENDOR at two very different frequencies, 9 and 94 GHz, that identify the iron sites of CoM-Hdr. We find direct evidence for a [4Fe-4S]3+ cluster, and we determine the sign of the 57Fe hyperfine couplings. The 57Fe isotropic hfc values suggest a complex interaction between the cluster and the CoM-SH substrate.
authors.affiliation: Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, J. W. Goethe University of Frankfurt, D-60439 Frankfurt, Germany. bennati@chemie.uni-frankfurt.de
authors.forename: Marina
authors.initials: M
authors.lastname: Bennati
authors.forename: Norbert
authors.initials: N
authors.lastname: Weiden
authors.forename: Klaus-P
authors.initials: KP
authors.lastname: Dinse
authors.forename: Reiner
authors.initials: R
authors.lastname: Hedderich
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D007503:Iron Isotopes; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D007553:Isotope Labeling; D017013:Methanobacteriaceae / Q000201:enzymology; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010769:Phosphothreonine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D007503:Iron Isotopes; D007506:Iron-Sulfur Proteins; C049349:7-mercaptoheptanoylthreonine phosphate; D010769:Phosphothreonine; D010088:Oxidoreductases; C066352:coenzyme M-7-merceptoheptanoylthreonine-phosphate-heterodisulfide hydrogenase; C087171:heterodisulfide reductase