Michael K. Chan received his B.S. in Chemistry from Harvey Mudd 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 that mediates the four-electron oxidation of water to dioxyen. He then moved to protein crystallography where as an NIH postdoctoral fellow he studied the structures of molybdenum and tungsten containing enzymes including the MoFe protein that performs the six-electron reduction of dinitrogen to ammonia. Current interests include efforts to elucidate the fundamental enzymes associated with carbon dioxide and methane biochemistry, and the development of novel biotechnologies based on the pyrrolysine incorporation system. Michael has been a faculty member at The Ohio State University since 1995. He is a recipient an NSF Career Award, an Alfred P. Sloan Foundation Fellowship, and most recently, an Ohio State Distinguished Scholar Award.

Perhaps the most important result from the Chan laboratory has been the discovery of pyrrolysine, the 22nd genetically-encoded (it uses the UAG codon) amino acid from the crystal structure of monomethylamine methyltransferase, MtmB - in collaboration with laboratory of Prof. Joseph Krzycki (1) (Fig. 1A). Our current structural analyses suggest that pyrrolysine acts to bind methylamines and position their methyl groups in an orientation where it can be abstracted by a corrinoid cofactor upon docking of its cognate corrinoid-binding protein, MtmC. Our lab subsequently synthesized the amino acid (2) (Fig. 1B), and the Krzycki group used this amino acid to show that it could be incorporated into recombinant protein (3).

Current projects include the structure determination of additional pyrrolysine-containing proteins as well as proteins involved in pyrrolysine incorporation, and the development of practical methods to use pyrrolysine and pyrrolysine analogs for novel biotechnologies. Our first reports detailing the use of this technology to site-specifically tag proteins have been recently published (4, 5).

Fig. 1. Pyrrolysine structural and chemical biology. (A) Observed conformational changed of pyrrolysine following reaction with methyl-hydroxylamine. (B) Chemical synthesis of L-pyrrolysine.	Fig. 2. Rh protein structure highlighting the channel, CO2 binding site, and residues proposed to link protein binding to the C-terminus to channel opening (5).

Structural and biochemical studies of membrane proteins

A relatively new focus of the lab has been the structural determination of membrane and membrane-inserting proteins. Our first success in this arena has been the structure of the N. europaea Rh protein (Fig. 2) in collaboration with Transmembrane Biosciences (TMB), a company in Pasadena, CA focused on developing novel membrane protein expression technologies. Like Amt proteins (ammonia channels), the structure of the N. europaea Rh protein revealed a homotrimer with a central substrate channel at the center of each subunit (6). The novel feature of the Rh protein structure was the presence of a cytoplasmic α-helix that oligomerizes to form a 3-helix bundle. Notably, a potential mechanism linking protein binding to the C-terminal helix to channel opening could be suggested from the structure. We are currently working to test this hypothesis by biochemical and structural methods.

Another major effort underway within this arena is the structural and biochemical study of Bacillus thuringiensis Cry toxins with Prof. Donald Dean (OSU). These proteins are soluble proteins that when activated insert into the membranes of insect midgut cells and promote insect death. We are interested in determining the structures of the membrane-inserted forms of these proteins, and in using this system to develop several novel biotechnologies.

Other Interests

Structural and Biochemical Studies of Proteins Involved in C1 Metabolism: Carbon dioxide and methane are the two major gases implicated in global warming. We are working to understand the biological systems that produce or degrade these gases (7, 8).

Bioinformatics: Recently we have been working with the Ralf Bundschuh laboratory to develop two new sequence alignment algorithms, LESTAT (9) and SIB-BLAST (10, 11). The latter, which exhibits improved signal-to-noise over PSI-BLAST, has been implemented as a web-based server - http://sib-blast.osc.edu

• Hao B, et al. (2002) A new UAG-encoded residue in the structure of a methanogen methyltransferase. Science 296:1462-66.
• Hao B, et al. (2004) Reactivity and chemical synthesis of L-pyrrolysine - the 22nd genetically encoded amino acid. Chem Biol 11:1317-24.
• Blight SK, et al. (2004) Direct charging of tRNACUA with pyrrolysine in vitro and in vivo. Nature 431:333-5.
• Fekner T, Li X, Lee MM, & Chan MK (2009) A pyrrolysine analogue for protein click chemistry. Angew Chem Int Ed Engl 48:1633-5.
• Li X, Fekner T, & Chan MK (2009) A pyrrolysine analogue for site-specific protein ubiquitination. Angew Chem Int Ed Engl 48:9184-7.
• Li X, Jayachandran S, Nguyen HH, & Chan MK (2007) Structure of the Nitrosomonas europaea Rh protein. Proc Natl Acad Sci USA 104:19279-84.
• Gong W, et al. (2008) Structure of the α2ε2 Ni-dependent CO dehydrogenase component of the Methanosarcina barkeri acetyl-CoA decarbonylase/synthase complex. Proc Natl Acad Sci USA 105:9558-63.
• Chan SI, et al. (2007) Redox potentiometry studies of particulate methane monooxygenase: support for a trinuclear copper cluster active site. Angew Chem Int Ed Engl 46:1992-4.
• Lee MM, Bundschuh R, & Chan MK (2008) Distant homology detection using a LEngth and STructure-based sequence Alignment Tool (LESTAT). Proteins 71:1409-19.
• Lee MM, Chan MK, & Bundschuh R (2008) Simple is beautiful: a straightforward approach to improve the delineation of true and false positives in PSI-BLAST searches. Bioinformatics 24:1339-43.
• Lee MM, Chan MK, & Bundschuh R (2009) SIB-BLAST: A web server for improved delineation of true and false positives in PSI-BLAST searches. Nucleic Acids Res., 37: W53-6.