B.Sc., Hebrew University in Jerusalem, Israel (1989) D.Sc., Technion - Israel Institute of Technology (1994) Postdoctoral Research Associate, University of California at Berkeley (1995-1999)

Physical Chemistry/Organic Chemistry

We study enzymes that are important in many biological processes such as de novo DNA synthesis. Many antibiotic and chemotherapeutic drugs target these enzymes. We employ an interdisciplinary approach to study enzyme mechanisms using various techniques in chemistry and molecular biology. Our group has a broad research interest in various aspects of enzyme catalysis: (1) we develop experimental methods to investigate the role of protein motions and quantum mechanics in enzyme catalyzed reactions; (2) we study molecular mechanisms of the recently discovered enzymes as attractive targets for novel antibiotic drugs; (3) we develop clinical applications of enzyme mechanisms, such as development of new P.E.T. imaging probes based on in vivo enzyme activities. In addition to common kinetic assays (e.g. UV-Vis spectroscopy, quench-flow experiments), we often use kinetic isotope effects (KIEs), structure and dynamics measurements (e.g. X-ray crystallography, NMR, 2D-IR measurements), and computer simulations to study enzymes. Students in the group will gain knowledge and hands-on experience in organic synthesis, molecular biology and protein purification, structural biology and drug design, enzyme assays and kinetics, isotope effect measurements, and theoretical calculations on enzyme catalysis.

Determination of concentration and activity of immobilized enzymes, Singh, P., Morris, H., Tivanski, A.V., Kohen, A.,* Anal., Biochem. 2015 (Just Accepted). Role of Dynamics in Enzyme Catalysis: Substantial vs. Semantic Controversies, Kohen, A.,* Acc. Chem. Res., 2015, 48, 466-473. Targeting the de novo Biosynthesis of Thymidylate for the Development of PET Probe for Pancreatic Cancer Imaging, Nilaweera, T., Saeed, M. and Kohen, A.* Biochemistry, 2015, 54, 1287–1293. Linking Protein Motion to Enzyme Catalysis, Singh, P., Abeysinghe, T., Kohen, A.,* Molecules, 2015, 20, 1192-1209. Free Energy Simulations of Active-Site Mutants of Dihydrofolate Reductase, Doron, D., Stojković, V., Gakhar, L., Kohen, A., Major,D.,* J. Phys. Chem. B., 2015, 119, 906–916. The Escherichia coli Dihydrofolate Reductase Catalyzed Proton and Hydride Transfers: Order and the Roles of Asp27 and Tyr100, Liu, C.T.,‡ Francis, K.,‡ Layfield , J., Huang, X., Hammes-Schiffer, S., Kohen, A.,* Benkovic, S.J.,* Proc. Nat., Acad. Sci. USA, 2014, 111, 18231–18236. Evoluntionalry Aspects of Enzyme Dynnamics, Klinman, J.P.* and Kohen. A.,* J. Biol. chem., 2014, 289, 30205-30212. Substrate Activation in Flavin-Dependent Thymidylate Synthase, Mishanina, T.V, Corcoran, J.M. and Kohen, A.,* J. Am. Chem. Soc. 2014, 136, 10597–10600. Concerted versus Step-Wise Mechanism in Thymidylate Synthase, Islam, Z., Strutzenberg, S.T., Gurevic, I. and Kohen, A.,* J. Am. Chem. Soc. 2014,136, 9850-9853. Protein Mass-modulated Effects in the Catalytic Mechanism of Dihydrofolate Reductase: Beyond Promoting Vibrations, Wang, Z., Singh, P.N., Czekster, M.C., Kohen, A.,* and Schramm, V.L. J. Am. Chem. Soc. 2014, 136, 8333-8341 Standards for the Reporting of Kinetic Isotope Effects in Enzymology, Francis, K. and Kohen, A.,* Perspectives in Science. 2014, 1, 110–120. Simulations of Remote Mutants of Dihydrofolate Reductase Reveal the Nature of a Network of Residues Coupled to Hydride Transfer, Roston, D., Kohen, A., Doron, D., Major, D.T., J. Comput. Chem. 2014, 35, 1411-1417. How Accurate are Transition States from Simulations of Enzymatic Reactions? Doron, D., Kohen, A., Nam, K., Major, D.T.,* J. Chem. Theory Comput., 2014, 10, 1863–1871. Protein Motions and the Activation of the C-H Bond Catalyzed by Dihydrofolate Reductase, Francis, K., Kohen, A.,* Curr. Opinion Chem. Biol., 2014, 21, 19–24. Stereospecific Multiple Isotopic Labeling of Benzyl Alcohol, Roston, D., Kohen, A.,* J. Labeled Comp. Radiopharma., 2014, 57, 75-77. Kinetic Isotope Effects as a Probe of Hydrogen Transfers to and from Common Enzymatic Cofactors, Roston, D., Islam, Z., and Kohen, A.,* Arch. Biochem. Biophys. 2014, 544, 96-104 Extension and limits of the network of couple motions correlated to hydride transfer in dihydrofolate reductase, Singh, P.N., Sen, A., Francis, K. and Kohen, A.,* J. Am. Chem. Soc. 2014,136, 2575-2582 Preservation of Protein Dynamics in Enzyme Evolution, Francis, K., Stojković, V., and Kohen, A.,* J. Biol. Chem. 2013, 288, 35961-35968. A critical test of the "Tunneling and Coupled Motion" Concept in Enzymatic Alcohol Oxidation, Roston, D. and Kohen, A.,* J. Am. Chem. Soc. 2013, 135, 13624-13627. Hydrogen Tunneling Links Protein Dynamics to Enzyme Catalysis Klinman, J.P.* and Kohen. A.,* Annu. Rev. Biochem., 2013, 82, 471-496