The Chan laboratory focuses on problems at the interface of chemistry and biology requiring the use of techniques spanning a wide range of disciplines. These include macromolecular crystallography, organic and inorganic synthesis, molecular cloning, protein overexpression and purification, and spectroscopy.

  

Synthetic Approaches    Our synthetic efforts are directed towards the development of catalysts for organic and biological transformations. The general approach is to design new ligands and molecules with the potential to induce novel chemistry and then synthesize them to test these concepts. One project currently funded by the NSF is the preparation of novel bis(benzimidazole) complexes for the asymmetric epoxidation of trans-olefins. A separate biomimetic project is directed towards the preparation of structural models of nitrogenase.

Structure of the manganese-bis(benzimidazole) complex

   Biological Targets

   The interests of the biological group are focused towards three main themes: determining the structures of the methyl-abstracting proteins from methanogens, understanding the mechanisms of signal transduction and ligand discrimination by oxygen-sensing proteins, and elucidating the structures and mechanisms of novel proteases that are targets for antibacterial and antiparasitic chemotherapy.

   Proteins from Methanogens.

   Methanogens are organisms that produce methane from a variety of C-1 carbon sources. We are currently studying two classes of proteins involved in abstracting the methyl group from substrates: (1) the acetyl-CoA decarbonylase synthase complex that acts on acetate, and (2) the monomethylamine methyltransferase (MtmB) that activates monomethylamine. Our interest in this area stems from the fact that the reactions catalyzed by these proteins involve organometallic intermediates - species that are rare in biology and thus provide opportunity for new discovery. Indeed, our recent structure determination of MtmB in collaboration with the Krzycki laboratory, led to the identification of pyrrolysine, the 22nd genetically encoded amino acid found in nature.

Structure of the MtmB homohexamer

Electron density of pyrrolysine.

Stick-diagram of pyrrolysine.

   O₂-Sensing Proteins

   Dioxygen is an important biomolecule that provides the oxidative energy for many biological processes. While oxygen is required for aerobic life, too much oxygen can be toxic. Hence, it is not surprising that nature has developed a variety of O₂-sensing proteins that regulate specific processes as a function of the O₂ level. Our group is currently working to determine the structures and mechanisms for several classes of oxygen sensing proteins. These include BjFixL, a heme-based O₂-sensor, and DcrH, a putative oxygen sensor with homology to hemerythrin.

  

Structure of the O2-sensing heme domain of BjFixL

Allosteric changes induced by O2-binding to BjFixLH

Structure of the O2-sensing domain of DcrH

   Structural Studies of Metalloproteases

  Another area of interest is the study of metalloproteases, proteins that utilize metals to catalyze the cleavage of amide-bonds in peptides and proteins. Our interest in these proteins stems from their potential as targets for antibacterial and antiparasitic chemotherapies, and from their possible biotechnological applications. We have completed the first crystal structures of two metalloproteases: the E. coli peptide deformylase and the P. furiosus carboxypeptidase.

  

Structure of E. coli PDF

Structure of the PDF-inhibitor complex

Structure of the P. furiosus carboxypeptidase

Hao, B., Gong, W., Ferguson, T.K., James, C.M., Krzycki, J.A., Chan, M.K., "Identification of novel UAG encoded residue: Structure of a methanogen methyltransferase", Science, 2002, 296, 1462-1466.

Arndt, J.W., Hao, B., Ramakrishnan, V., Chen, T., Chan, S. I., Chan,, M.K., "Structure of the hyperthermophilic Pyrococcus furiosus carboxypeptidase", Structure, 2002, 10, 215-224.

Arndt, J.W., Gong, W., Zhong, X., Liu, J., Lin, Z., Schowalter, A.K., Paxson, C., Tsai, M.-D., Chan, M.K., "Insight into the Catalytic Mechanism of DNA Polymerase: Structures of Intermediate Complexes", Biochemistry, 2001, 40, 5368- 5375.

Payra, P. Hung, S.-C., Kwok, W.-H., Johnston, D. Gallucci, J., Chan, M.K., "Structural, Magnetic and Catalytic Properties of a Self-Recognized μ-Oxo-Bridged Diiron(III) Bis(benzimidazole) Complex", Inorg. Chem., 2001, 40, 4036-4039.

Kwok, W.H., Zhang, H., Payra, P., Duan, M., Hung, S.-C., Johnston, D.H., Gallucci, J., Skrzypczak-Jankun, E., Chan, M.K., "Synthesis and characterization of the dimethyl-substituted bisbenzimidazole ligand and its manganese complex", Inorg. Chem., 2000, 39, 2367-2376.

Gong, W., Hao, B., Chan, M.K., "New mechanistic insights from structural studies of the oxygen-sensing domain of Bradyrhizobium japonicum FixL", Biochemistry, 2000, 3955-3962.

Hao, B., Gong, W., Rajagopalan, P.T.R., Zhou, Y., Pei, D., Chan. M.K., "Structural basis for the design of antibiotics targeting peptide deformylase", Biochemistry, 1999, 38, 4712-4719.

Gong, W., Hao, B., Mansy, S.S., Gonzalez, G. Gilles-Gonzalez, M.A., Chan, M.K., "Structure of a biological oxygen sensor: a new mechanism for heme-driven signal transduction", Proc. Natl. Acad. Sci. USA, 1998, 95, 15177-15182.

  Michael K. Chan received his B.S. in Chemistry from Harvey College, and his Ph.D. in Inorganic Chemistry from the University of California, Berkeley, working with William H. Armstrong on functional models of the Photosystem II Oxygen Evolving Complex. He then moved to protein crystallography where as an NIH postdoctoral fellow he studied the structures of molybdenum and tungsten containing enzymes. Michael has been a faculty member at The Ohio State University since 1995. He is a recent recipient of an NSF Career Award and is currently an Alfred P. Sloan Foundation Fellow.