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Published on: November 15, 2013
Structural Insights into the Loss-of-Function R288H Mutant of Human PPARγ
Daichi Egawa1, Taku Ogiso1, Kimina Nishikata1
1Laboratory of Drug Design and Medicinal Chemistry, Showa Pharmaceutical University.
Abstract:
Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and the molecular target of thiazolidinedione-class antidiabetic drugs. It has been reported that the loss of function R288H mutation in the human PPARγ ligand-binding domain (LBD) may be associated with the onset of colon cancer. A previous in vitro study showed that this mutation dampens 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2, a natural PPARγ agonist)-dependent transcriptional activation; however, it is poorly understood why the function of the R288H mutant is impaired and what role this arginine (Arg) residue plays. In this study, we found that the apo-form of R288H PPARγ mutant displays several altered conformational arrangements of the amino acid side chains in LBD: 1) the loss of a salt bridge between Arg288 and Glu295 leads to increased helix 3 movement; 2) closer proximity of Gln286 and His449 via a hydrogen bond, and closer proximity of Cys285 and Phe363 via hydrophobic interaction, stabilize the helix 3-helix 11 interaction; and 3) there is steric hindrance between Cys285/Gln286/Ser289/His449 and the flexible ligands 15d-PGJ2, 6-oxotetracosahexaenoic acid (6-oxoTHA), and 17-oxodocosahexaenoic acid (17-oxoDHA). These results suggest why Arg288 plays an important role in ligand binding and why the R288H mutation is disadvantageous for flexible ligand binding.
Insights
The R288H mutation in Peroxisome proliferator-activated receptor gamma (PPARγ) impairs its function by altering ligand-binding domain conformation. This structural change hinders flexible ligand binding, potentially contributing to colon cancer development.
Area of Science:
- Molecular biology
- Structural biology
- Biochemistry
Background:
- Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and target for antidiabetic drugs.
- A loss-of-function R288H mutation in PPARγ's ligand-binding domain (LBD) is linked to colon cancer.
- The R288H mutation reduces transcriptional activation by natural PPARγ agonists like 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2).
Purpose of the Study:
- To elucidate the structural mechanisms underlying the impaired function of the R288H PPARγ mutant.
- To understand the specific role of arginine (Arg) residue 288 in PPARγ function and ligand binding.
Main Methods:
- Analysis of the apo-form of the R288H PPARγ mutant.
- Investigating conformational changes in the LBD using structural analysis.
- Assessing interactions between amino acid side chains and flexible ligands.
Main Results:
- The R288H mutation disrupts the Arg288-Glu295 salt bridge, increasing helix 3 movement.
- Stabilization of the helix 3-helix 11 interaction occurs through new hydrogen and hydrophobic bonds.
- Steric hindrance is observed between mutated residues and flexible ligands (15d-PGJ2, 6-oxoTHA, 17-oxoDHA).
Conclusions:
- Arg288 is crucial for effective ligand binding in PPARγ.
- The R288H mutation confers disadvantageous structural changes, impairing flexible ligand binding.
- These findings provide insights into the molecular basis of R288H-associated colon cancer risk.
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