Abstract Details

Geometric and Electronic Structure of the Ni(I) and Ni(III) Intermediates of Methyl-coenzyme M Reductase
Abstract ID	W_EXAFS-09
Presenter	Ritimukta  Sarangi
Presentation Type	EXAFS Workshop - SSRL
Full Author List	R. Sarangi (1) , S. P. Ragsdale (2) , M. Dey (2)
Affiliations	(1) Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford, CA-94025 (2) University of Michigan Medical School, Michigan University, Ann Arbor, MI-48109
Category	Bio/Life Sciences
Abstract	Methanogens are strictly anaerobic microbes that form methane to generate cellular energy.1 Methyl-coenzyme M reductase (MCR) catalyzes the final step of methane formation in these organisms by the reaction of methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoyl-threonine phosphate (HSCoB).1 The active site of MCR has been shown to contain a Ni bound flexible corphin cofactor (F430), which has been proposed to go through Ni(I), Ni(II) and Ni(III) oxidation states during the catalytic mechanism of methane formation. The crystal structure of the Ni(II) form has been solved2 and its electronic structure has been well characterized but only indirect experimental evidence is available about the active site structure of the Ni(I) and Ni(III) forms. A combination of Ni K-pre-edge and edge analysis, time dependent core level DFT calculations and EXAFS analysis will be presented, which help shed light on the active site geometry of the elusive Ni(I) and Ni(III) forms of MCR. The data reveal uniquely different active sites in all three forms of MCR and give insight into the mechanism of methane generation. The importance of a combination of spectroscopic and theoretical techniques to arrive at the final active site structures of the Ni(I) and Ni(III) forms will be highlighted.
Footnotes	1) DiMarco, A. A., Bobik, T. A., and Wolfe, R. S. Annu. Rev. Biochem., 1990, 59, 355-394 2) Ermler, U.; Grabarse, W.; Shima, S.; Goubeaud, M.; Thauer, R. K. Science, 1997, 278, 1457-1462.
Funding Acknowledgement	This work was performed at the Stanford Synchrotron Radiation Laboratory, which is funded by the DOE Office of Basic Energy Sciences. The SSRL Structural Molecular Biology Program is supported by the NIH National Center for Research Resources, Biomedical Technology Program and by the DOE Office of Biological and Environmental Research.