Chemistry Faculty:
Michael
K. Johnson,
Ph.D.
Distinguished Research Professor
Phone: 706-542-9378
E-mail: johnson@chem.uga.edu
Biographical Information
Co-director, Center for Metalloenzyme Studies
Ph.D., University of East Anglia (England), 1977
Research Interests
Our research concerns the role and assembly 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 assembly mechanism of metallocenters and the the electronic and structural properties of metal centers that confer selective and specific catalytic activity present fascinating challenges to inorganic chemists. In our work we use a range of spectroscopic techniques to probe the characteristic properties of transition metal centers, i.e. color, paramagnetism, etc. These include electron paramagnetic resonance (EPR), resonance Raman, FTIR, and UV/visible/near-IR absorption and natural and magnetically induced circular dichroism (CD and MCD). We also collaborate with other groups for Mossbauer, ENDOR, X-ray absorption and X-ray crystallography studies of proteins prepared in our laboratory.
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 mechanism of assembly and the role of the metal center(s) in the molecular mechanism of catalysis or electron transfer. Currently our research program focuses on the assembly and functions of iron-sulfur clusters, metalloenzymes involved in the oxidative stress response, and the role of heme, nickel, molybdenum, and tungsten centers in a range of proteins and enzymes. Funding for this work is provided by two grants from the National Institutes of Health.
Selected Publications
Chandramouli, K., Unciuleac, M.-C., Naik, S., Dean, D.R., Huynh, B.H., Johnson, M.K., "Formation and Properties of [4Fe-4S] Clusters on the IscU Scaffold Protein," Biochemistry 2007, 46, 6804-6811.
Unciuleac, M.-C., Chandramouli, K., Naik, S., Mayer, S., Huynh, B.H., Johnson, M.K., Dean, D.R., "In vitro Activation of Apo-Aconitase Using a [4Fe-4S] Cluster-Loaded Form of the IscU [Fe-S] Cluster Scaffolding Protein," Biochemistry 2007, 46, 6812-6821.
Chandramouli, K., Johnson, M.K., "HscA and HscB stimulate [2Fe-2S] cluster transfer from IscU to apo-ferredoxin in an ATP-dependent reaction," Biochemistry 2006, 45, 11087-11095.
Yang, T.-C.,McNaughton, R.L., Clay, M.D., Jenney, F.E., Krishnan, R., Kurtz, D.M., Adams, M.W.W., Johnson, M.K., Hoffman, B.M., "Comparing the electronic properties of the low-spin cyano-ferric active sites of superoxide reductase and P450cam using ENDOR spectroscopy and DFT calculations," J. Am. Chem. Soc. 2006, 128, 16566-16578.
Johnson, D., Dean, D.R., Smith, A.D., Johnson, M.K., "Structure, Function and Formation of Biological Iron-Sulfur Clusters," Annu. Rev. Biochem. 2005, 74, 247-281.
Walters, E.M., Garcia-Serres, R., Jameson, G.N.L., Glauser, D.A., Bourquin, F., Manieri, W., Schurmann, P., Huynh, B.H., Johnson, M.K., "Spectroscopic Characterization of Site-Specific [4Fe-4S] Cluster Chemistry in Ferredoxin:Thioredoxin Reductase: Implications for the Catalytic Mechanism ," J. Am. Chem. Soc. 2005, 127, 9612-9624.
Johnson, M.K., Smith, A.D. "Iron-Sulfur Proteins," in Encyclopedia of Inorganic Chemistry, Second Edition (King, R.B., ed.) 2005.
Cosper, M.M., Jameson, G.N.L., Hernandez, H.L., Krebs, C., Huynh, B.H., Johnson, M.K., "Characterization of the Cofactor Composition of Escherichia coli Biotin Synthase," Biochemistry 2004, 43, 2007-2021.