My laboratory uses approaches derived from both chemistry and biology to investigate molecular mechanisms of cellular biochemistry and physiology. Projects are organized around the themes of purine/pyrimidine metabolism and protease action and include problems in inhibitor design, protein engineering and cellular metabolism. Most projects have clinical relevance. Techniques vary with the particular project, and can entail molecular biology, single molecule experiments, organic synthesis, protein crystallography and NMR spectroscopy as well as protein purification, enzyme kinetics and mutagenesis. Some of our ongoing projects are outlined below. For more information, please see the lab web site.

Pathophysiological mechanisms of retinal disease. Many inherited retinal diseases are caused by mutations in proteins of the visual cycle, which can easily explain why disease is photoreceptor-specific. However, retinal disease can also result from mutations in widely expressed proteins. The photoreceptor-specific effects of these mutations are perplexing and pathophysiological mechanisms are undefined. One such protein is inosine monophosphate dehydrogenase type 1 (IMPDH1), which catalyzes a key step in guanine nucleotide biosynthesis. The effects of the IMPDH1 mutations cannot be explained by the loss of enzyme activity. We have recently discovered that IMPDH binds nucleic acids and demonstrated that the disease-causing mutations perturb nucleic acid binding. We are now investigating how this defect causes the specific apoptosis of photoreceptor cells with the aim of developing strategies for therapy.

Drug Targets in Cryptosporidium parvum. This eukaryotic parasite is an emerging opportunistic pathogen and potential bio-warfare agent. The C. parvum oocyte is resistant to the usual methods of water treatment, which has caused spectacular outbreaks such as the infection of 40% of the inhabitants of Milwaukee in 1993. C. parvum is resistant to the usual antiparasitic drugs and currently used chemotherapy is ineffective. We are mining the genome of C. parvum to reconstruct the parasite metabolic pathways and identify new targets for drug development. Our biochemical characterization of C. parvum IMP dehydrogenase suggests that this enzyme is a promising target. We are currently developing inhibitors specific for the parasite enzyme by screening for novel lead compounds. We are also trying to determine the structure of this enzyme with x-ray crystallography that will enable the use of structure-based approaches for drug design.
 
Dynamic structural determinants of drug selectivity. While drug specificity is generally attributed simply to the topology of the protein target, the contribution of dynamic processes is becoming hard to ignore. We are investigating the dynamic properties of inhibitor selectivity in two remarkable systems: IMP dehydrogenase and serpins.

IMP dehydrogenase (IMPDH) is a target for immunosuppressive, antiviral and anticancer chemotherapy. The enzyme undergoes a large conformational change in mid-catalytic cycle that is blocked by several drugs. Selectivity is determined by how well the drug binds relative to the equilibrium of this conformational change. This work involves detailed kinetic characterization, structure determination and various biophysical techniques to study protein dynamics.

Serpins are ubiquitous inhibitors of serine proteases that regulate blood coagulation, fibrinolysis and many other physiological processes. Serpins react with their target protease to form a stable adduct in a process that involves a 70 Å translocation and structural rearrangements of both protease and inhibitor. We are collaborating with Anne Gershenson to investigate the mechanism of serpin inhibition with single molecule experiments. This work builds on our classic experiments delineating the structural determinants of specificity in serine proteases.

Mechanistic enzymology. My laboratory has a long-standing interest in the mechanisms of enzyme catalysis. The current system of interest is the methionine salvage pathway, which plays an important role in cell proliferation and involves several challenging chemical transformations. The penultimate step of this pathway is catalyzed by acireductone dioxygenase (ARD). This remarkable protein catalyzes two different oxidative cleavage reactions depending on the metal at the active site. One of these reactions is part of the methionine salvage pathway, and the other produces carbon monoxide, a gaseous neurotransmitter. We are characterizing the human homolog of ARD in collaboration with Tom Pochapsky.

Selected Publications:

IMP dehydrogenase: structure, mechanism, and inhibition. Hedstrom L. Chem Rev. 2009 Jul;109(7):2903-28.
 
Retinal isoforms of inosine 5'-monophosphate dehydrogenase type 1 are poor nucleic acid binding proteins. Xu D, Cobb G, Spellicy CJ, Bowne SJ, Daiger SP, Hedstrom L. Arch Biochem Biophys. 2008 Apr 15;472(2):100-4. [abstract]

An enzymatic atavist revealed in dual pathways for water activation. Min D, Josephine HR, Li H, Lakner C, MacPherson IS, Naylor GJ, et al. PLoS Biol. 2008;6(8):e206. [full text in PubMed Central] [abstract]

Targeting a prokaryotic protein in a eukaryotic pathogen: identification of lead compounds against cryptosporidiosis. Umejiego NN, Gollapalli D, Sharling L, Volftsun A, Lu J, Benjamin NN, et al. Chem Biol. 2008;15(1):70-7. [abstract]

A kinetic alignment of orthologous inosine-5'-monophosphate dehydrogenases. Riera TV, Wang W, Josephine HR, Hedstrom L. Biochemistry. 2008;47(33):8689-96. [abstract]

IMP dehydrogenase type 1 associates with polyribosomes translating rhodopsin mRNA. Mortimer SE, Xu D, McGrew D, Hamaguchi N, Lim HC, Bowne SJ, et al. J Biol Chem. 2008;283(52):36354-60. [full text in PubMed Central] [abstract]

IMP dehydrogenase-linked retinitis pigmentosa. Hedstrom L. Nucleosides Nucleotides Nucleic Acids. 2008;27(6):839-49. [abstract]

Short-lived protease serpin complexes: partial disruption of the rat trypsin active site. Liu L, Mushero N, Hedstrom L, Gershenson A. Protein Sci. 2007;16(11):2403-11. [abstract]

Regulation of nonproteolytic active site formation in plasminogen. Gladysheva IP, Sazonova IY, Houng A, Hedstrom L, Reed GL. Biochemistry. 2007;46(30):8879-87. [abstract]

Novel methylenephosphophosphonate analogues of mycophenolic adenine dinucleotide. Inhibition of inosine monophosphate dehydrogenase. Rejman D, Olesiak M, Chen L, Patterson SE, Wilson D, Jayaram HN, et al. J Med Chem. 2006;49(16):5018-22. [abstract]

Conformational distributions of protease-serpin complexes: a partially translocated complex. Liu L, Mushero N, Hedstrom L, Gershenson A. Biochemistry. 2006;45(36):10865-72. [abstract]

IMP dehydrogenase: structural schizophrenia and an unusual base. Hedstrom L, Gan L. Curr Opin Chem Biol. 2006;10(5):520-5. [abstract]

Spectrum and frequency of mutations in IMPDH1 associated with autosomal dominant retinitis pigmentosa and leber congenital amaurosis. Bowne SJ, Sullivan LS, Mortimer SE, Hedstrom L, Zhu J, Spellicy CJ, et al. Invest Ophthalmol Vis Sci. 2006;47(1):34-42. [full text in PubMed Central] [abstract]

View Complete Publication List on PubMed: Liz Hedstrom