Education, Honors, Awards

  • Assistant Professor, James Madison University (2014-present)
  • Postdoctoral Fellow, Argonne National Laboratory (2011-2014)
  • Postdoctoral Fellow, University of Illinois at Urbana-Champaign (2009-10)
  • Ph.D., Biophysics and Computational Biology, University of Illinois at Urbana-Champaign (2009)

Research Interests

  • Charge and energy transfer in proteins
  • Small- and wide-angle X-ray scattering
  • Time-resolved laser spectroscopy

Research Description

Most of our work is focused on biochemical and biophysical studies of cytochromes, a large class of heme-containing proteins involved in energy transduction and biological catalysis. We use a wide range of experimental and computational techniques including: DNA cloning and mutagenesis, recombinant protein expression and isolation, time-resolved absorbance and fluorescence spectroscopy, mass spectroscopy, isothermal calorimetry, small- and wide-angle X-ray scattering, and molecular dynamics simulations.

A large set of our experimental projects involves various members of the cytochrome c7 family which we use as model systems to elucidate molecular mechanisms of photo-induced charge transfer. Besides fundamental understanding of underlying physical and chemical processes, we use these principles to build better enzymes for artificial photosynthesis. Some of this work has been done in collaboration with scientists from Argonne National Lab.

The second set of project is focused on isolation and biophysical/biochemical characterization of new c-type cytochromes from Geobacter sulfurreducens. This anaerobic bacterium uses iron oxide (“rust”) for respiration instead of oxygen. The exact biochemical pathway has not been mapped yet but it is expected to involve its unusually large number (>80) of c-type cytochromes.  In addition to mapping those pathways, we hope to understand molecular mechanisms of cytochrome adhesion to solid surfaces and to exploit them in various biotechnological applications.

The final set of projects is dealing with structure-function relationship in ubiquinol: cytochrome c oxidoreductase (Complex III, bc1 complex). The bc1 complex is a large (250-500kDa) homodimeric enzyme involved in respiration. Depending on the specie, each monomer contains between 3 and 12 different subunits. It is estimated that up to 80% of energy in Biosphere flows through bc1 and related enzymes. Not surprisingly, even slight diversion of the energy flow may produce significant quantities of highly damaging reactive oxygen species (ROS) and bc1 is believed to be one of the two major producers of ROS in mitochondria. Similarly, the significance of the bc1 complex in respiration and substantial bc1 structural differences between parasite and host species make it a promising target for antibiotics. 

Selected Recent Publications

  • Young, B.H., Caldwell, T.A., McKenzie, A.M., Kokhan, O., Berndsen, C.E. (2016) Characterization of the structure and catalytic activity of Legionella pneumophila VipF, Proteins, 84, 1422-1430.
  • Du Pont, K.E., McKenzie, A.M., Kokhan, O., Sumner, I., Berndsen, C.E. (2016) The disulfide bonds within BST-2 enhance tensile strength during viral tethering, Biochemistry, 55, 940-947.
  • Dantas, J.M., Kokhan, O., Pokkuluri, P.R., Salgueiro, C.A. (2015) Molecular interaction studies revealed the bifunctional behavior of triheme cytochrome PpcA from Geobacter sulfurreducens  the redox active analog of humic substances. Biochim. Biophys. Acta – Bioenergetics, 1847, 1129-1138.
  • Kokhan, O., Ponomarenko, N., Pokkuluri, R.P., Schiffer, M., Mulfort, K.L., Tiede, D.M. (2015) Bidirecetional photoinduced electron transfer in Ruthenium(II)-tris-bipyridyl modified PpcA, a multi-heme c-type cytochrome from Geobacter sulfurreducens. J. Phys. Chem. B, 119, 7612-7624.
  • Kokhan, O., Ponomarenko, N., Pokkuluri, P.R., Schiffer, M., Tiede, D.M. (2014) Multimerization of solution-state proteins by tetrakis(4-sulfonatophenyl) porphyrin, Biochemistry, 53, 5070-5079.
  • Du, P., Kokhan, O., Chapman, K.W., Chupas, P.J., Tiede, D.M. (2012) Elucidating the domain structure of the cobalt oxide water splitting catalyst by X-ray pair distribution function analysis, J. Am. Chem. Soc., 134(27), 11096-11099.
  • Kokhan, O., Wraight, C.A., Tajkhorshid, E. (2010) The binding interface of cytochrome c and cytochrome c1 in the bc1 complex: rationalizing the role of key residues, Biophys. J., 99(8), 2647-2656.
  • Kokhan, O., Shinkarev. V.P., Wraight, C.A. (2010) Binding of imidazole to the heme of cytochrome c1 and inhibition of the bc1 complex from Rhodobacter sphaeroides I. Equilibrium and modeling studies, J. Biol. Chem., 285(29), 22513-22521. 


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