title: Direct interaction of coenzyme M with the active-site Fe-S cluster of heterodisulfide reductase.
abstract: Heterodisulfide reductase (HDR) catalyzes the formation of coenzyme M (CoM-SH) and coenzyme B (CoB-SH) by the reversible reduction of the heterodisulfide, CoM-S-S-CoB. This reaction recycles the two thiol coenzymes involved in the final step of microbial methanogenesis. Electron paramagnetic resonance (EPR) and variable-temperature magnetic circular dichroism spectroscopic experiments on oxidized HDR incubated with CoM-SH revealed a S=1/2 [4Fe-4S]3) cluster, the EPR spectrum of which is broadened in the presence of CoM-33SH [Duin, E.C., Madadi-Kahkesh, S., Hedderich, R., Clay, M.D. and Johnson, M.K. (2002) Heterodisulfide reductase from Methanothermobacter marburgensis contains an active-site [4Fe-4S] cluster that is directly involved in mediating heterodisulfide reduction. FEBS Lett. 512, 263-268; Duin, E.C., Bauer, C., Jaun, B. and Hedderich, R. (2003) Coenzyme M binds to a [4Fe-4S] cluster in the active site of heterodisulfide reductase as deduced from EPR studies with the [33S]coenzyme M-treated enzyme. FEBS Lett. 538, 81-84]. These results provide indirect evidence that the disulfide binds to the iron-sulfur cluster during reduction. We report here direct structural evidence for this interaction from Se X-ray absorption spectroscopic investigation of HDR treated with the selenium analog of coenzyme M (CoM-SeH). Se K edge extended X-ray absorption fine structure confirms a direct interaction of the Se in CoM-SeH-treated HDR with an Fe atom of the Fe-S cluster at an Fe-Se distance of 2.4A.
authors.affiliation: Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia, Athens, GA 30602-2556, USA.
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Shokes
authors.forename: Evert C
authors.initials: EC
authors.lastname: Duin
authors.forename: Carsten
authors.initials: C
authors.lastname: Bauer
authors.forename: Bernhard
authors.initials: B
authors.lastname: Jaun
authors.forename: Reiner
authors.initials: R
authors.lastname: Hedderich
authors.forename: Jürgen
authors.initials: J
authors.lastname: Koch
authors.forename: Robert A
authors.initials: RA
authors.lastname: Scott
mesh_terms: D001665:Binding Sites; D004220:Disulfides / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D015080:Mesna / Q000737:chemistry* / Q000378:metabolism; D017014:Methanobacterium / Q000201:enzymology*; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D013057:Spectrum Analysis; D014965:X-Rays
chemical_list: D004220:Disulfides; D007506:Iron-Sulfur Proteins; D007501:Iron; D010088:Oxidoreductases; C087171:heterodisulfide reductase; D015080:Mesna