Spin Density and Coenzyme M Coordination Geometry of the ox1 Form of Methyl-Coenzyme M Reductase: A Pulse EPR Study
详细信息 查看全文
- 作者：Jeffrey Harmer ; Cinzia Finazzo ; Rafal Piskorski ; Carsten Bauer ; Bernhard Jaun ; Evert C. Duin ; Meike Goenrich ; Rudolf K. Thauer ; Sabine Van Doorslaer ; and Arthur Schweiger
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：December 21, 2005
- 年：2005
- 卷：127
- 期：50
- 页码：17744 - 17755
- 全文大小：245K
- 年卷期：v.127,no.50(December 21, 2005)
- ISSN：1520-5126
文摘
Methyl-coenzyme M reductase (MCR) catalyses the reduction of methyl-coenzyme M (CH3-S-CoM) with coenzyme B (H-S-CoB) to CH4 and CoM-S-S-CoB in methanogenic archaea. Here we presenta pulse EPR study of the "ready" form MCRox1, providing a detailed description of the spin density and thecoordination of coenzyme M (CoM) to the Ni cofactor F430. To achieve this, MCR was purified from cellsgrown in a 61Ni enriched medium and samples were prepared in D2O with the substrate analogue CoMeither deuterated in the 
-position or with 33S in the thiol group. To obtain the magnetic parameters ENDORand HYSCORE measurements were done at X- and Q-band, and CW EPR, at X- and W-band. The hyperfinecouplings of the -protons of CoM indicate that the nickel to -proton distances in MCRox1 are very similarto those in Ni(II)-MCRox1-silent, and thus the position of CoM relative to F430 is very similar in both species.Our thiolate sulfur and nickel EPR data prove a Ni-S coordination, with an unpaired spin density on thesulfur of 7 ± 3%. These results highlight the redox-active or noninnocent nature of the sulfur ligand on theoxidation state. Assuming that MCRox1 is oxidized relative to the Ni(II) species, the complex is formallybest described as a Ni(III) (d7) thiolate in resonance with a thiyl radical/high-spin Ni(II) complex, NiIII- -SR
NiII-
SR.
-position or with 33S in the thiol group. To obtain the magnetic parameters ENDORand HYSCORE measurements were done at X- and Q-band, and CW EPR, at X- and W-band. The hyperfinecouplings of the -protons of CoM indicate that the nickel to -proton distances in MCRox1 are very similarto those in Ni(II)-MCRox1-silent, and thus the position of CoM relative to F430 is very similar in both species.Our thiolate sulfur and nickel EPR data prove a Ni-S coordination, with an unpaired spin density on thesulfur of 7 ± 3%. These results highlight the redox-active or noninnocent nature of the sulfur ligand on theoxidation state. Assuming that MCRox1 is oxidized relative to the Ni(II) species, the complex is formallybest described as a Ni(III) (d7) thiolate in resonance with a thiyl radical/high-spin Ni(II) complex, NiIII- -SR NiII-SR.