Group Members
Group Business

The Coward Laboratory


Research in our laboratory involves synthetic and mechanistic organic chemistry employed in combination with mechanistic biochemistry.  Three different types of enzymes have been selected for study:  folypoly-g-glutamate synthetase/g-glutamyl hydrolase, glycosyltransferases such as oligosaccharyltransferase, and glutathionylspermidine synthetase/amidase.

Folic acid is a key vitamin in human nutrition.  Cellular folates contain a reduced pteridine heterocycle and a poly-g-glutamyl peptide "tail".  Two enzymes, folypolyglutamate synthetase (FPGS) and g-glutamyl hydrolase (GH), being studied by our research group, catalyze the biosynthesis and hydrolytic cleavage, respectively, of the polyglutamyl portion of cellular folates and antifolate drugs.  Recent research has involved the synthesis of several fluoro- and phosphoamino acids and their incorporation into folates and antifolate drugs.  These effortes have led to the synthesis of fluoropeptides or phosphapeptides for biochemical investigation as inhibitors or stimulators of the reactions catalyzed by FPGS or GH.  In collaborative research, our new compounds are beina used in intact mammalian cells to assess the role of polyglutamate formation and hydrolysis in normal folate-dependent one-carbon biochemistry and also in the pharmacology of antifolate drugs used in the treatment of cancer. 

Trypanothione (TSH), found exclusively in trypanosomatid parasites, is a derivative of the ubiquitous antioxidant, glutathione (GSH).  The biosynthesis of TSH involves bis-acylation of the polyamine, spermidine, by GSH.  The intermediate monoacylated GSH, glutathionylspermidine (Gsp), but not TSH, is found in E. coli and both its synthesis and hydrolysis are effected by a unique bifunctional enzyme, Gsp synthetase/amidase.  We have extended the phophapeptide research mentioned above to the development of new inhibitors of TSH biosynthesis as possible anti-trypanosomal drugs.  Based on an understanding of the mechanism of Gsp we have designed and synthesized specific phophapeptide inhibitors of the synthetase domain and, in collaborative research, have used these compounds to study the regulation of catalysis by this bifunctional enzyme.

Oligosaccharyltransferase (OST), an enzyme that catalyzes the N-glycosylation of proteins, is a membrane-bound protein that we isolate from yeast.  Initial research has centered on the use of synthetically accessible small substrates, characterization of the chemical structure of the glycopeptide product, and the use of isotopically labeled peptide substrates for mechanistic studies.  Recent research has focused on the use of larger peptides and proteins as substrates and has led to extensive studies with invertase-derived peptides of varying length.  Kinetic data combined with structure-activity data has allowed us to develope a working hypothesis concerning peptide substrate recognition by OST.  Current research also involves the synthesis of a variety of substrates and inhibitors designed to answer specific mechanistic questions.  As in the research with the folate polyglutamates and trypanothione, the goal here is to understand the mechanism of this reaction in sufficient detail that it will be feasible to design and synthesize potent and specific inhibitors for use in the study of cellular glycoprotein biosynthesis.

Last updated: March 2003
Site maintained by
S. Anspaugh, anspaugh@umich.edu