Faculty

We are studying the microbial metabolism of one-carbon compounds (CO, CO2 , methane) and xenobiotics (e.g., PCBs); oxygen sensing in the human carotid body; and the roles of metal ions in biology, including the mechanisms of nickel, B12 , heme, and iron-sulfur enzymes. We use transient and steady-state kinetics, spectroscopy, and molecular biology to uncover mechanistic information. The research is funded by NIH and DOE.

We are studying the mechanism of methyl coenzyme M reductase, which contains a nickel tetrapyrrole and is responsible for all biologically generated methane. We recently trapped an alkyl-Ni intermediate and are elucidating a mechanism that appears to involve both SN2 and radical chemistry. We are characterizing a nickel-iron-sulfur enzyme called CO dehydrogenase (CODH) that enables microbial growth on CO2 and the toxic gas CO. CODH complexes another nickel iron-sulfur enzyme, acetyl-CoA synthase (ACS), forming a macromolecular machine that generates CO from CO2 as an intermediate. During catalysis, CO migrates from the CODH active site through a 70 Å channel to the ACS active site, which catalyzes acetyl-CoA synthesis. We also are studying methyl and proton transfer in a methyltransferase and a vitamin B12/iron-sulfur protein and characterizing how enzymes like pyruvate ferredoxin oxidoreductase catalyze reactions involving radical intermediates.

We are studying the human heme oxygenase-2 (HO-2), which plays an important role in heme homeostasis and in generating CO, a signal molecule that regulates many physiological processess. We recently determined the first crystal structure of HO-2 in collaboration with George Phillips (U. Wisconsin) and uncovered a thiol/disulfide redox switch that regulates heme binding. We are evaluating its physiological role and collaborating with Jeff Martens (Dept Pharmacology) to determine how HO-2 regulates a potassium channel, enabling HO-2 control of oxygen levels in the blood stream.

Certain anaerobic microbes use chlorinated aromatics like PCBs as electron acceptors, coupling dehalogenation to energy conservation. We are characterizing the mechanisms of the Vitamin B12 containing enzyme (CprA) that catalyzes dehalogenation, and the transcriptional activator (CprK) that regulates expression of proteins involved in metabolizing these xenobiotics through effector binding and a thiol/disulfide redox switch.

Awards

Elected Fellow of the American Academy of Microbiology (2006)
Outstanding Research and Creativity Award from the University of Nebraska System (2003)
Charles E. Bessey Professorship (2003)
Shaw Scholar Award, Milwaukee Foundation (1987-92)

Representative Publications

1. Seravalli, J. and Ragsdale, S.W., "Pulse-chase studies of the synthesis of acetyl-coenzyme A by carbon monoxide dehydrogenase/acetyl-CoA synthase: Evidence for a random mechanism of methyl and CO addition", J. Biol. Chem., 2008, 283, 8384-8394. [Full Article]

2. Doukov, T.I., Blasiak, L.C., Seravalli, J., Ragsdale, S.W., and Drennan, C.L. "Xenon in and at the end of the tunnel of bifunctional carbon monoxide dehydrogenase/acetyl-CoA synthase", Biochem., 2008, 47, 3474-3483. [Full Article]

3. Doukov, T.I., Hemmi, H., Drennan, C.L. and Ragsdale, S.W. "Structural And Kinetic Evidence For An Extended Hydrogen Bonding Network In Catalysis Of Methyl Group Transfer: Role Of An Active Site Asparagine Residue In Activation Of Methyl Transfer By Methyltransferases", J. Biol. Chem., 2007, 282, 6609. (paper of the week & faculty of 1000 choice) [Full Article]

4. Yi, L. and Ragsdale, S. W., "Evidence that the heme regulatory motifs in heme oxygenase-2 serve as a thiol/disulfide redox switch regulating heme binding", J. Biol. Chem., 2007, 282, 20156-21067. [Full Article]

5. Bianchetti, C.M, Li, Y., Ragsdale, S.W., and Philips, G.N., Jr. "Comparison of apo- and heme-bound crystal structures of a truncated human heme oxygenase-2", J. Biol. Chem., 2007, 282, 37624-37631. [Full Article]

6. Ragsdale, S.W. "Metals and their scaffolds to promote difficult enzymatic reactions", Chem. Rev., 2006, 106, 3317. [Full Article]

7. Kunz, R.C., Horng, Y.-C. and Ragsdale, S.W., "Spectroscopic and Kinetic Studies of the Reaction of Bromopropanesulfonate with Methyl-Coenzyme M Reductase", J. Biol. Chem., 2006, 281, 34663. [Full Article]

8. Pop, S.M., Gupta, N., Raza, A.S. and Ragsdale, S.W. "Transcriptional activation of dehalorespiration: identification of redox-active cysteines regulating dimerization and DNA binding", J. Biol. Chem., 2006, 281, 26382. [Full Article]