The long-term goal of this proposal is to understand the structural mechanism of the constitutive androstane receptor (CAR). CAR belongs to the nuclear receptor superfamily of proteins. These are hormone-modulated transcription factors that direct almost every aspect of human physiology. CAR is constitutively active in the absence of ligand. Small molecules have been identified that modulate CAR activity. The steroidal molecule, androstanol, functions as an inverse agonist and inhibits the constitutive activity of CAR. Another molecule, TCPOBOP, rescues CAR from the androstanol-mediated repression and can enhance CAR activity. We hypothesize that the CAR structure employs unique, but subtle, modifications from the canonical nuclear receptor structural fold that results in this distinctive behavior. We hypothesize that the three states of CAR, the inactive, androstanol-bound, the active, apo, and the TCPOBOP-bound highly active states are linked by an allosteric mechanism.
In Specific Aim 1 we propose to compare the structures of apo CAR with androstenol-bound CAR.
In Specific Aim 2, we will compare the CAR:TCPOBOP to apo and androstanol-bound CAR structures.
In Specific Aim 3, we will study the mechanism of CAR allosterism by performing structure-based point mutations and binding and activity assays on these mutants. CAR has been shown to direct the transcription of the CYP2 and CYP3 gene products, which belong to the cytochrome P50 class of enzymes. These enzymes are responsible for the metabolism of xenobiotics such as pharmaceutical drugs. CAR has been directly implicated in the metabolism of the analgesic, acetaminophen (commercial nomenclature: Tylenol) other pharmaceutical products. Understanding the CAR molecular mechanism is of great significance in nuclear receptor biology with broad implications in the pharmacology of these proteins. Because of its involvement in metabolism of therapeutics, CAR is itself an attractive target for the design of small molecule ligands that can both enhance or diminish its transcriptional activity.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK066394-02
Application #
7027690
Study Section
Molecular and Cellular Endocrinology Study Section (MCE)
Program Officer
Margolis, Ronald N
Project Start
2005-05-01
Project End
2009-04-30
Budget Start
2006-05-01
Budget End
2007-04-30
Support Year
2
Fiscal Year
2006
Total Cost
$239,851
Indirect Cost
Name
University of Tennessee Knoxville
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
003387891
City
Knoxville
State
TN
Country
United States
Zip Code
37996
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Wright, Edward; Busby, Scott A; Wisecarver, Sarah et al. (2011) Helix 11 dynamics is critical for constitutive androstane receptor activity. Structure 19:37-44
Putcha, Balananda-Dhurjati K; Fernandez, Elias J (2009) Direct interdomain interactions can mediate allosterism in the thyroid receptor. J Biol Chem 284:22517-24
Wright, Edward; Vincent, Jeremy; Fernandez, Elias J (2007) Thermodynamic characterization of the interaction between CAR-RXR and SRC-1 peptide by isothermal titration calorimetry. Biochemistry 46:862-70
Vincent, Jeremy; Shan, Li; Fan, Ming et al. (2005) Crystallographic analysis of murine constitutive androstane receptor ligand-binding domain complexed with 5alpha-androst-16-en-3alpha-ol. Acta Crystallogr Sect F Struct Biol Cryst Commun 61:156-9
Shan, Li; Vincent, Jeremy; Brunzelle, Joseph S et al. (2004) Structure of the murine constitutive androstane receptor complexed to androstenol: a molecular basis for inverse agonism. Mol Cell 16:907-17