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 Ċ 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:
Nwakaso N. Umejiego, Deviprasad Gollapalli, Lisa Sharling, Anna Volftsun, Jennifer Lu,
Nicole N. Benjamin, Adam H. Stroupe, Thomas V. Riera, Boris Striepen and Lizbeth Hedstrom. (Jan. 2008) Targeting a prokaryotic protein in a eukaryotic pathogen: identification of lead compounds against Cryptosporidiosis.
Chem Biol. 2008 Jan;15:70-7. [abstract].
Liu L, Mushero N, Hedstrom L, Gershenson A. (2006) Conformational
distributions of protease-serpin complexes: a partially
translocated complex. Biochemistry. 2006 Sep 12;45(36):10865-72.
[abstract]
Hedstrom L, Gan L. (2006) IMP dehydrogenase: structural
schizophrenia and an unusual base. Curr Opin Chem Biol. 2006 Oct;10(5):520-5. Epub 2006 Aug 17. Review. [abstract]
Rejman D, Olesiak M, Chen L, Patterson SE, Wilson D, Jayaram
HN, Hedstrom L, Pankiewicz KW. (2006) Novel methylenephosphophosphonate
analogues of mycophenolic adenine dinucleotide. Inhibition
of inosine monophosphate dehydrogenase. J Med Chem. 2006
Aug 10;49(16):5018-22. [abstract]
Guillén Schlippe YV & Hedstrom L. (2005) Is Arg418 the
Catalytic Base Required for the Hydrolysis Step of the IMP
Dehydrogenase Reaction? Biochemistry, 2005 Sep 6;44(35):11700-7.
[abstract]
Mortimer SE & Hedstrom L. (2005) Autosomal Dominant Retinitis
Pigmentosa Mutations in Inosine Monophosphate Dehydrogenase
Type I Disrupt Nucleic Acid Binding. Biochemical Journal
390: 41-47. [abstract]
Köhler GA, Gong X, Bentink S, Theiss S, Pagani GM, Agabian
N & Hedstrom L. (2005) Candida albicans IMP Dehydrogenase:
the functional basis of mycophenolic acid resistance. J.
Biol. Chem. 280: 11295-11302.
Guillén Schlippe YV & Hedstrom L. (2005) A Twisted Base?
the Role of Arginine in Enzyme-Catalyzed Proton Abstractions.
Archives Biochemistry and Biophysics, 43: 266-278.
[abstract]
Umejiego NN, Li C, Riera T, Hedstrom L, Striepen B. (2004)
Cryptosporidium parvum IMP dehydrogenase: Identification
of functional, structural and dynamic properties that can
be exploited for drug design. J Biol Chem., 279:
40320-40327. [abstract]
Striepen B, Pruijssers AJ, Huang J, Li C, Gubbels MJ, Umejiego
NN, Hedstrom L, Kissinger JC.(2004) Gene transfer in the
evolution of parasite nucleotide biosynthesis. Proc Natl
Acad Sci U S A. 101(9):3154-9. [abstract]
Guillen Schlippe YV, Riera TV, Seyedsayamdost MR, Hedstrom
L. Substitution of the Conserved Arg-Tyr Dyad Selectively
Disrupts the Hydrolysis Phase of the IMP Dehydrogenase Reaction.
Biochemistry. 43(15):4511-21 (2004). [abstract]
Pasternak A, White A, Jeffrey C, Medina N, Cahoon M, Ringe
D, Hedstrom, L. The energetic cost of induced fit
catalysis: crystal structures of trypsinogen mutants with
enhanced activity and inhibitor binding. Protein Science 10, 1331-1342 (2001). [abstract]
View Complete Publication List on PubMed:
Liz Hedstrom
Last review: February 19, 2008. E-mail
comments or questions to the webmaster.
