This proposal focuses on mechanistic studies of the key enzymes in the Wood-Ljungdahl pathway of CO/CO2 fixation and acetyi-CoA synthesis. These enzymes are CO dehydrogenase (CODH), acetyi-CoA synthase (ACS), the corrinoid iron-sulfur protein (CFeSP) and its cognate methyltransferase (MeTr), and pyruvate ferredoxin oxidoreductase (PFOR). Studies of this pathway will continue to enrich the areas of microbiology, biochemistry and bioinorganic chemistry by revealing significant new insights into the structures of macromolecular channels, previously unknown metal clusters, unusual roles of low-valent nickel and cobalt ions as nucleophiles, novel biochemical roles of Coenzyme A, organometallic complexes as intermediates in enzymatic catalysis, and large conformational movements that permit active sites to interface with multiple binding partners and redox mediators. We will use spectroscopic, mutagenesis and kinetic experiments to characterize the catalytic mechanisms of CODH and ACS, to elucidate the properties of hydrophobic pockets in the CO channel that connect the CODH and ACS active sites and provide insight into the conformational changes that coordinate opening and closing of the gas channel. For ACS, we have recently developed methods to generate nearly stoichiometric amounts of each intermediate in the catalytic cycle and plan to determine their structural and electronic properties. In studies of the CFeSP and MeTr, we plan to elucidate the protein-protein complexes and conformational changes that drive methyl and electron transfer. During one catalytic cycle, the C-terminal B12-binding domain (CTD) of the CFeSP must interface with MeTr, the small subunit of the CFeSP and the A-cluster of ACS, as well as the FeS domain of the CFeSP when reductive activation is required. We will determine the crystal structures and perform small-angle X-ray scattering experiments of the key complexes between the CFeSP and its binding partners. We also will perform mechanistic and structural studies of chimeric constructs in which the CTD is linked to each of its binding partners and of these separately expressed domains. In studies of PFOR (and its CoA-independent homolog, oxalate oxidoreductase), we plan to characterize the complex between CODH and PFOR and its role in CO2 channeling and electron transfer. We also will elucidate the novel role of CoA in causing a 1 00,000-fold increase in rate of electron transfer from a substrate-induced radical intermediate to an integral iron-sulfur cluster.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Method to Extend Research in Time (MERIT) Award (R37)
Project #
Application #
Study Section
Special Emphasis Panel (NSS)
Program Officer
Anderson, Vernon
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Michigan Ann Arbor
Domestic Higher Education
Ann Arbor
United States
Zip Code
Ragsdale, Stephen W (2018) Stealth reactions driving carbon fixation. Science 359:517-518
Burton, Rodney; Can, Mehmet; Esckilsen, Daniel et al. (2018) Production and properties of enzymes that activate and produce carbon monoxide. Methods Enzymol 613:297-324
Chen, Percival Yang-Ting; Aman, Heather; Can, Mehmet et al. (2018) Binding site for coenzyme A revealed in the structure of pyruvate:ferredoxin oxidoreductase from Moorella thermoacetica. Proc Natl Acad Sci U S A 115:3846-3851
Pierce, Elizabeth; Mansoorabadi, Steven O; Can, Mehmet et al. (2017) Properties of Intermediates in the Catalytic Cycle of Oxalate Oxidoreductase and Its Suicide Inactivation by Pyruvate. Biochemistry 56:2824-2835
Can, Mehmet; Giles, Logan J; Ragsdale, Stephen W et al. (2017) X-ray Absorption Spectroscopy Reveals an Organometallic Ni-C Bond in the CO-Treated Form of Acetyl-CoA Synthase. Biochemistry 56:1248-1260
Gibson, Marcus I; Chen, Percival Yang-Ting; Johnson, Aileen C et al. (2016) One-carbon chemistry of oxalate oxidoreductase captured by X-ray crystallography. Proc Natl Acad Sci U S A 113:320-5
Gibson, Marcus I; Brignole, Edward J; Pierce, Elizabeth et al. (2015) The Structure of an Oxalate Oxidoreductase Provides Insight into Microbial 2-Oxoacid Metabolism. Biochemistry 54:4112-20
Wang, Vincent C-C; Islam, Shams T A; Can, Mehmet et al. (2015) Investigations by Protein Film Electrochemistry of Alternative Reactions of Nickel-Containing Carbon Monoxide Dehydrogenase. J Phys Chem B 119:13690-7
Can, Mehmet; Armstrong, Fraser A; Ragsdale, Stephen W (2014) Structure, function, and mechanism of the nickel metalloenzymes, CO dehydrogenase, and acetyl-CoA synthase. Chem Rev 114:4149-74
Wang, Vincent C-C; Ragsdale, Stephen W; Armstrong, Fraser A (2014) Investigations of the efficient electrocatalytic interconversions of carbon dioxide and carbon monoxide by nickel-containing carbon monoxide dehydrogenases. Met Ions Life Sci 14:71-97

Showing the most recent 10 out of 27 publications