Education

Nanjing University, China, Ph.D. in Bioinorganic Chemistry, 1998

Professional Experience

2006-present: Assistant Professor of Medicinal Chemistry, College of Pharmacy, University of New Mexico, Albuquerque, NM

2003-2005: Research Scientist, Department of Chemistry, University of Arizona, Tucson, AZ

2000 – 2002: Postdoctoral Research Associate with Professor John H. Enemark, Department of Chemistry, University of Arizona, Tucson, Arizona

1998 – 2000: Postdoctoral Fellow with Professor Yuanzhi Xu, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China

Awards and Fellowships

2007: Young Investigator Award, Gordon Research Conference on Nitric Oxide

2000 – 2002: Japan Society for the Promotion of Science Postdoctoral Fellowship (declined)

1998 – 2000: China Postdoctoral Science Foundation Postdoctoral Fellowship

1999: Asia-Pacific EPR Society Distinguished Service Award

Research Interests

Nitric oxide synthase (NOS) is the enzyme responsible for the synthesis of nitric oxide (NO), a major physiological messenger molecule involved in the nervous, immune, and cardiovascular systems. Owing to the potency and importance of NO as a regulatory molecule, NOS is a complex enzyme under stringent control. Interdomain electron transfer (IET) reactions in NOS are essential in controlling NO synthesis (Fig. 1). It is thus imperative to understand the mechanism of electron transfer in NOS, which have yet to be completely defined. Our long-term goals are to critically explore the mechanism of NOS regulation at the molecular level by investigating the crucial IET processes, in order to identify the key sequences for controlling the NOS function.

Fig. 1. Electron flow in NOS (as shown in red arrows). In eNOS/nNOS, CaM-binding facilitates IET between FAD and FMN within the reductase domain, and triggers the inter-subunit FMN-heme IET (reaction 2).

A major focus is to investigate mechanism of electron transfer in the NOS output state using an integrated approach of laser flash photolysis, pulsed EPR and site-directed mutagenesis. It is proposed that the calmodulin (CaM) activation of NO synthesis in endothelial and neuronal NOS (eNOS and nNOS) requires a conformational change of the flavin mononucleotide (FMN) domain from its original electron-accepting (input) state to a new electron-donating (output) state (Fig. 2). The putative output state is envisioned as a complex between the FMN binding and oxygenase domains, thus facilitating efficient IET between the FMN and the catalytic heme in the oxygenase domain.

Fig. 2. Tethered shuttle model: FMN binding domain shuttles between the FAD domain and heme-containing oxygenase domain. Left: input state; Right: putative output state. The FMN motion is controlled by CaM binding to and dissociation from NOS. The tethers correspond to the FAD-FMN and FMN-oxygenase connectors.

The FMN-heme IET within the NOS output state is essential for NO synthesis. However, the mechanism of the output state formation remains unclear, which thus constitutes a critical barrier for understanding the CaM controlled NOS catalytic mechanisms more completely. The focus of our study is to investigate the mechanisms of CaM-activated output state formation at the molecular level. We hypothesize that specific CaM binding and productive FMN/heme interactions are two critical structural determinants for formation of the NOS output state. This hypothesis will be tested by quantitating the FMN-heme IET kinetics in a well-validated model of the NOS output state through two complementary and synergistic Aims. We have developed innovative laser flash photolysis approaches to directly determine the FMN-heme IET within the NOS output state. The proposed studies will significantly improve the fundamental understanding of NOS regulation, and will provide important new insight as to how NOS might be selectively modulated for therapeutic purposes.

Selected Publications:

Feng, Changjian; Tollin, Gordon; Enemark, John H. (2007) Sulfite oxidizing enzymes, Biochim. Biophys. Acta, 1774, 527-539. Review

Feng, Changjian; Tollin, Gordon; Hazzard, James T.; Nahm, Nickolas J.; Guillemette J. Guy; Salerno, John C.; Ghosh, Dipak K. (2007) Direct measurement by laser flash photolysis of intraprotein electron transfer in a rat neuronal nitric oxide synthase, J. Am. Chem. Soc., 129, 5621 - 5629.

Feng, Changjian; Tollin, Gordon; Holliday, Michael A.; Thomas, Clayton; Salerno, John C.; Enemark, John H.; Ghosh, Dipak K. (2006) Intraprotein electron transfer in a two-domain construct of neuronal nitric oxide synthase: The output state in nitric oxide formation, Biochemistry 45, 6354-6362.

Feng, Changjian; Thomas, Clayton; Holliday, Michael A.; Tollin, Gordon; Salerno, John C.; Ghosh, Dipak K.; Enemark, John. H. (2006) Direct Measurement by Laser Flash Photolysis of Intramolecular Electron Transfer in a Two-Domain Construct of Murine Inducible Nitric Oxide Synthase. Journal of the American Chemical Society 128, 3808-3811.

Feng, Changjian; Wilson, Heather L.; Tollin, Gordon; Astashkin, Andrei A; Hazzard, James T.; Rajagopalan, K. V.; Enemark, John H. (2005) The pathogenic human sulfite oxidase mutants G473D and A208D are defective in intramolecular electron transfer. Biochemistry 44, 13734 - 13743.

Astashkin, Andrei, V., Feng, Changjian, Raitsimring, Arnold, M., Enemark, John, H. (2005) "17O ESEEM evidence for exchange of the axial oxo ligand in the molybdenum center of the high pH form of sulfite oxidase." Journal of the American Chemical Society 127, 502 - 503.

Raitsimring, Arnold M.; Kappler, Ulrike; Feng, Changjian; Astashkin, Andrei V.; Enemark, John H. (2005) Pulsed EPR studies of a bacterial sulfite-oxidizing enzyme with pH-invariant hyperfine interactions from exchangeable protons. Inorg. Chem. 44, 7283-7285.

Astashkin, Andrei V.; Hood, Brian L.; Feng, Changjian; Hille, Russ; Mendel, Ralf R.; Raitsimring, Arnold M.; Enemark, John H. (2005) Structures of the Mo(V) forms of sulfite oxidase from Arabidopsis thaliana by pulsed EPR spectroscopy. Biochemistry 44, 13274-13281.

Feng, Changjian; Kappler, Ulrike; Tollin, Gordon; Enemark, John H. (2003) Intramolecular electron transfer in a bacterial sulfite dehydrogenase. Journal of the American Chemical Society 125, 14696 -14697.

Feng, Changjian; Wilson, Heather L.; Hurley, John K.; Hazzard, James, T.; Tollin, Gordon; Rajagopalan, K. V.; Enemark, John H. (2003) Essential role of conserved arginine 160 in intramolecular electron transfer in human sulfite oxidase. Biochemistry 42, 12235-12242.

Feng, Changjian; Wilson, Heather L.; Hurley, John K.; Hazzard, James, T.; Tollin, Gordon; Rajagopalan, K. V.; Enemark, John H. (2003) Role of conserved tyrosine 343 in intramolecular electron transfer in human sulfite oxidase. Journal of Biological Chemistry 278, 2913-2920.

Raitsimring, Arnold M.; Astashkin, Andrei V.; Feng, Changjian; Enemark, John. H.; Nelson, Kimberly Johnson; Rajagopalan, K. V. (2003) Pulsed EPR studies of the exchangeable proton at the molybdenum center of dimethyl sulfoxide reductase. Journal of Biological Inorganic Chemistry 8, 95-104.

Feng, Changjian; Kedia, Rohit V.; Hazzard, James T.; Hurley, John K.; Tollin, Gordon; Enemark, John H. (2002) Effect of solution viscosity on intramolecular electron transfer in sulfite oxidase. Biochemistry 41, 5816-5821.

Elliott, Sean J.; McElhaney, Anne E.; Feng, Changjian; Enemark, John H.; Armstrong, Fraser A. (2002) A voltammetric study of interdomain electron transfer within sulfite oxidase. Journal of the American Chemical Society 124, 11612 -11613.

Astashkin, Andrei V.; Raitsimring, Arnold M.; Feng, Changjian; Johnson, Jean L.; Rajagopalan, K. V.; Enemark, John H. (2002) Pulsed EPR studies of nonexchangeable protons near the Mo (V) center of sulfite oxidase: Direct detection of the ?-proton of the coordinated cysteinyl residue and structural implications for the active site. Journal of the American Chemical Society 124, 6109-6118