Nature uses highly reactive radicals to carry out a diverse set of biochemical functions, many of which are essen- tial to maintaining proper human health. These potent biological radical reactions need to be carried out safely, producing essential specific products, without dangerous side reactions occurring. A large number of such rad- ical reactions are performed by the family of radical SAM enzymes, which use a [4Fe-4S] center with a bound S-adenosylmethionine (SAM) molecule to generate a strongly oxidizing 5'-deoxyadenosyl radical which can in turn drive a large number of difficult chemical reactions. We will target mechanistic aspects of several classes of radical SAM enzymes. Biotin synthase is a radical SAM enzyme that catalyzes the final step in the biosynthesis of the vitamin biotin. A set of Fe-S and radical SAM maturase enzymes are used to build the unique Fe-S center of Fe-Fe hydrogenase, an enzyme which catalyzes the important reduction of protons to dihydrogen and vice versa. And radical SAM enzymes are used to modify many bases in transfer RNA, improving codon-anticodon recognition in order to make protein synthesis more reliable. We are specifically interested in a radical SAM enzyme QueE that is essential for generating 7-deazapurines. This proposal describes a magnetic resonance spectroscopic approach to study such diverse radical SAM enzymes. Specifically, we are using electron para- magnetic resonance (EPR) spectroscopy, which can precisely measure the magnetic environment of unpaired electrons in the radical SAM Fe-S clusters, in the organic radicals that these clusters generate, and in secondary metal centers that are involved in the reactions in many of these enzymes.

Public Health Relevance

Radicals, high-energy chemical species with unpaired electrons, can cause deleterious reactions in biology, including those adversely affecting human health. At the same time the potent reactions radicals can carry out are necessary for a large number of crucial enzymes. We are studying a set of these radical reactions to learn how biological metal centers and radicals work in concert to safely harness the power of radical reaction chemistry in the superfamily of Radical SAM Enzymes.

National Institute of Health (NIH)
Research Project (R01)
Project #
Application #
Study Section
Macromolecular Structure and Function A Study Section (MSFA)
Program Officer
Anderson, Vernon
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Davis
Schools of Arts and Sciences
United States
Zip Code
Stich, Troy A; Myers, William K; Britt, R David (2014) Paramagnetic intermediates generated by radical S-adenosylmethionine (SAM) enzymes. Acc Chem Res 47:2235-43
Myers, William K; Stich, Troy A; Suess, Daniel L M et al. (2014) The cyanide ligands of [FeFe] hydrogenase: pulse EPR studies of (13)C and (15)N-labeled H-cluster. J Am Chem Soc 136:12237-40