Michael K. JohnsonResearch Professor of Chemistry and Biochemistry & Molecular Biology
Co-Director, Center for Metalloenzyme Studies
Professor Johnson received B.A. (1974) and M.A.(1977) degrees from Cambridge University, England, and M.S. (1975) and Ph.D. (1978) degrees from the University of East Anglia, England. He was a U. K. Science Research Council Postdoctoral Fellow at the University of East Anglia and came to the U.S. in 1980 as a postdoctoral research associate at Princeton University. Before joining the faculty in 1987, he was an Assistant an Associate Professor at Louisiana State University and an Alfred P. Sloan Research Fellow.
Our research concerns the role of transition metal centers in metalloenzymes and metalloproteins. Metal ions are now known to constitute the active sites of at least one third of all enzymes and determining the electronic and structural properties that confer selective and specific catalytic activity presents a fascinating challenge to the inorganic chemist. In our work we use a range of spectroscopic/magnetic techniques to probe the characteristic properties of transition metal centers, i.e. color, paramagnetism, etc. These include electron paramagnetic resonance (EPR), resonance Raman, FTIR, optical absorption, natural and magnetically induced circular dichroism (CD and MCD), and magnetic susceptibility. The information content of these techniques is often complementary and leads to a detailed understanding of the electronic, magnetic, and structural properties of metal centers imbedded in a large polypeptide macromolecule. The goal is complete understanding of the role of the metal center(s) in the molecular mechanism of catalysis, electron transfer or regulation.
Currently our research program focuses on iron-sulfur clusters as well as molybdenum, tungsten and heme centers in a range of proteins and enzymes. Enzymes and proteins currently under investigation include nitrogenases (M-Fe-S cluster active site, where M = Mo, V, or Fe), Fe-S cluster assembly proteins, a wide range of Mo or W oxotranferases, ferredoxin thioredoxin reductase (Fe-S/disulfide active site), biotin synthase (Fe-S active site), pyruvate formate-lyase activating enzyme (Fe-S active site), ferrochelatase (regulatory Fe-S cluster), nitric oxide synthase (heme active site), the CO-sensing CooA protein (heme active site), a novel type of superoxide dismutase called neelaredoxin (mononuclear Fe center), and a range of bacterial and archeal ferredoxins and rubredoxins. The elucidation of structural, electronic and functional information from spectroscopic properties is facilitated by parallel studies of mutant proteins with site-directed changes in residues close to the metal and by comparative studies of appropriate synthetic inorganic complexes. We work closely with biochemical coworkers in the design of mutant proteins and part of our own research effort isconcerned with the synthesis of inorganic analog complexes that mimic the metal sites in metallobiomolecules. Funding for this work is provided by the National Institutes of Health and the National Science Foundation.
"Biological and Synthetic [Fe3S4] Clusters", Johnson, M. K.; Duderstadt, R. E.; Duin, E. C. Adv. Inorg. Chem. 1999, 47, 1-82.
"Role of the [Fe4S4] Cluster in Mediating Disulfide Reduction in Spinach Ferredoxin:Thioredoxin Reductase", Staples, C. R.; Gardet-Salvi, L.; Stritt-Etter, A.-L. ; Telser, J.; Hoffman, B. M.; Schürmann, P.; Knaff, D. B.; Johnson, M. K. Biochemistry 1998, 37, 4612-4620.
"Active-site Structures and Catalytic Mechanism of Rhodobacter sphaeroides Dimethylsulfoxide Reductase as Revealed by Resonance Raman Spectroscopy", Garton, S. D.; Hilton, J.; Oku, H.; Crouse, B. R.; Rajagopalan, K. V.; Johnson, M. K. J. Am. Chem. Soc. 1997, 119, 12906-12916.