Enzymes that harness the extreme reactivity of electron-deficient free radical species carry out some of the most difficult chemical reactions in biology. The regio- and stereo-selectivity achieved by these enzymes defies long-held ideas that radical reactions are non-specific. This class includes the following: ribonucleotide reductases, which catalyze the first unique step in DNA biosynthesis, prostaglandin H-synthase, the target of aspirin and other nonsteroidal anti-inflammatory drugs, the S-adenosylmethionine-dependent enzymes, with over six-hundred members that catalyze a wide range of radicalmediated redox reactions, and the coenzyme B12 (adenosylcobalamin)-dependent enzyme superfamily, whose members catalyze metabolite covalent bond rearrangements. The common primary step in these chemically-disparate catalyses is metal-assisted generation of an electron-deficient organic radical. This initiator radical, either by itself or through secondary radical species, promotes hydrogen atom abstraction from the substrate to form a substratebased radical, opening a new reaction channel that facilitates transformation to the product. An outstanding issue is how the radical pair is stabilized against rapid recombination to achieve productive reaction in high yield. Elucidating the basic principles of how protein and cofactor guide radical generation, stabilization, intra-protein radical migration, and radical rearrangement will be sustained focuses of the proposed studies. The coenzyem B12-dependent enzymes, and ethanolamine ammonia-lyase specifically, have been selected for scrutiny. The contributions of molecular structure and dynamics to enzyme function will be studied by using techniques of pulsed-electron paramagnetic resonance and visible/near-infrared absorption spectroscopy, in cryotrapped and time-resolved systems on time scales ranging from picoseconds to hours. The fundamental insights and novel methods developed will promote identification and characterization of radical intermediates in other biological reactions, inform the design of programmed radical reactivity, and assist molecular-therapeutic efforts to combat pernicious free radical processes.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
High Priority, Short Term Project Award (R56)
Project #
2R56DK054514-11
Application #
7564374
Study Section
Macromolecular Structure and Function A Study Section (MSFA)
Program Officer
Sechi, Salvatore
Project Start
1998-03-15
Project End
2008-06-30
Budget Start
2008-02-15
Budget End
2008-06-30
Support Year
11
Fiscal Year
2008
Total Cost
$59,288
Indirect Cost
Name
Emory University
Department
Physics
Type
Schools of Arts and Sciences
DUNS #
066469933
City
Atlanta
State
GA
Country
United States
Zip Code
30322