Insights into the Mechanism of Partial Agonism: CRYSTAL STRUCTURES OF THE PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR LIGAND-BINDING DOMAIN IN THE COMPLEX WITH TWO ENANTIOMERIC LIGANDS (original) (raw)
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International Union of Pharmacology. LXI. Peroxisome Proliferator-Activated Receptors
Pharmacological Reviews, 2006
The three peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors of the nuclear hormone receptor superfamily. They share a high degree of structural homology with all members of the superfamily, particularly in the DNA-binding domain and ligand-and cofactor-binding domain. Many cellular and systemic roles have been attributed to these receptors, reaching far beyond the stimulation of peroxisome proliferation in rodents after which they were initially named. PPARs exhibit broad, isotype-specific tissue expression patterns. PPAR␣ is expressed at high levels in organs with significant catabolism of fatty acids. PPAR/␦ has the broadest expression pattern, and the levels of expression in certain tissues depend on the extent of cell proliferation and differentiation. PPAR␥ is expressed as two isoforms, of which PPAR␥2i s found at high levels in the adipose tissues, whereas PPAR␥1 has a broader expression pattern. Transcrip-tional regulation by PPARs requires heterodimerization with the retinoid X receptor (RXR). When activated by a ligand, the dimer modulates transcription via binding to a specific DNA sequence element called a peroxisome proliferator response element (PPRE) in the promoter region of target genes. A wide variety of natural or synthetic compounds was identified as PPAR ligands. Among the synthetic ligands, the lipidlowering drugs, fibrates, and the insulin sensitizers, thiazolidinediones, are PPAR␣ and PPAR␥ agonists, respectively, which underscores the important role of PPARs as therapeutic targets. Transcriptional control by PPAR/RXR heterodimers also requires interaction with coregulator complexes. Thus, selective action of PPARs in vivo results from the interplay at a given time point between expression levels of each of the three PPAR and RXR isotypes, affinity for a specific promoter PPRE, and ligand and cofactor availabilities. proliferator response element; LBD, ligand-binding domain; HDL-C, high-density lipoprotein cholesterol.
Ligand-Induced Stabilization and Activation of Peroxisome Proliferator-Activated Receptor γ
Chemical Biology & Drug Design, 2008
Peroxisome proliferator-activated receptor c belongs to the nuclear receptor superfamily and is activated by the antidiabetic drugs rosiglitazone and pioglitazone. Ligand-independent constitutive activity of peroxisome proliferator-activated receptor c is also demonstrated. X-ray crystallographic structures show that the active or inactive conformations of the receptor are determined by the position of helix 12 in the C-terminal end. In this study, molecular dynamics simulations were used to gain molecular insight into the activation process and the structural stability of inactive and active peroxisome proliferator-activated receptor c receptor structure. The simulations showed: (i) during molecular dynamics simulations without agonist at the active site, the receptor structure with helix 12 in a position corresponding to activated receptor structure was structurally more stable than with helix 12 in a position corresponding to inactive receptor structure, which may contribute to the constitutive activity of the receptor; (ii) docosahexenoic acid stabilized the active receptor conformation more efficiently than the glitazones; (iii) docosahexenoic acid, but not glitazones, induced structural changes into the inactive receptor structure such that helix 12 was shifted into a position more similar to that of an active receptor structure, which indicate that docosahexenoic acid is a more effective peroxisome proliferator-activated receptor c agonist than the glitazones.
Ligand-induced Peroxisome Proliferator-activated Receptor alpha Conformational Change
Journal of Biological Chemistry, 1997
Structurally diverse peroxisome proliferators and related compounds that have been demonstrated to induce the ligand-dependent transcriptional activation function of mouse peroxisome proliferator-activated receptor ␣ (mPPAR␣) in transfection experiments were tested for the ability to induce conformational changes within mPPAR␣ in vitro. WY-14,643, 5,8,11,14-eicosatetraynoic acid, LY-171883, and clofibric acid all directly induced mPPAR␣ conformational changes as evidenced by a differential protease sensitivity assay. Carboxylterminal truncation mutagenesis of mPPAR␣ differentially affected the ability of these ligands to induce conformational changes suggesting that PPAR ligands may make distinct contacts with the receptor. Direct interaction of peroxisome proliferators and related compounds with, and the resulting conformational alteration(s) in, mPPAR␣ may facilitate interaction of the receptor with transcriptional intermediary factors and/or the general transcription machinery and, thus, may underlie the molecular basis of ligand-dependent transcriptional activation mediated by mPPAR␣.
Ligand-induced Peroxisome Proliferator-activated Receptor α Conformational Change
Journal of Biological Chemistry, 1997
Structurally diverse peroxisome proliferators and related compounds that have been demonstrated to induce the ligand-dependent transcriptional activation function of mouse peroxisome proliferator-activated receptor ␣ (mPPAR␣) in transfection experiments were tested for the ability to induce conformational changes within mPPAR␣ in vitro. WY-14,643, 5,8,11,14-eicosatetraynoic acid, LY-171883, and clofibric acid all directly induced mPPAR␣ conformational changes as evidenced by a differential protease sensitivity assay. Carboxylterminal truncation mutagenesis of mPPAR␣ differentially affected the ability of these ligands to induce conformational changes suggesting that PPAR ligands may make distinct contacts with the receptor. Direct interaction of peroxisome proliferators and related compounds with, and the resulting conformational alteration(s) in, mPPAR␣ may facilitate interaction of the receptor with transcriptional intermediary factors and/or the general transcription machinery and, thus, may underlie the molecular basis of ligand-dependent transcriptional activation mediated by mPPAR␣.
Journal of Structural Biology, 2015
Peroxisome Proliferator-Activated Receptors (PPARs) are ligand-dependent transcription factors that control various functions in human organism, including the control of glucose and lipid metabolism. PPARc is a target of TZD agonists, clinically used to improve insulin sensitivity whereas fibrates, PPARa ligands, lower serum triglyceride levels. We report here the structural studies of GL479, a synthetic dual PPARa/c agonist, designed by a combination of clofibric acid skeleton and a phenyldiazenyl moiety, as bioisosteric replacement of stilbene group, in complex with both PPARa and PPARc receptors. GL479 was previously reported as a partial agonist of PPARc and a full agonist of PPARa with high affinity for both PPARs. Our structural studies reveal different binding modes of GL479 to PPARa and PPARc, which may explain the distinct activation behaviors observed for each receptor. In both cases the ligand interacts with a Tyr located at helix 12 (H12), resulting in the receptor active conformation. In the complex with PPARa, GL479 occupies the same region of the ligand-binding pocket (LBP) observed for other full agonists, whereas GL479 bound to PPARc displays a new binding mode. Our results indicate a novel region of PPARs LBP that may be explored for the design of partial agonists as well dual PPARa/c agonists that combine, simultaneously, the therapeutic effects of the treatment of insulin resistance and dyslipidemia.
L-764406 Is a Partial Agonist of Human Peroxisome Proliferator-activated Receptor γ
Journal of Biological Chemistry, 1999
Insulin-sensitizing thiazolidinedione (TZD) compounds are high affinity ligands for a member of the nuclear receptor family, peroxisome proliferator-activated receptor (PPAR) ␥. A scintillation proximity assay for measurement of 3 H-radiolabeled TZD binding to human PPAR␥ under homogeneous conditions was developed. Using this approach, a novel non-TZD compound (L-764406) was shown to be a potent (apparent binding IC 50 of 70 nM) PPAR␥ ligand. Preincubation of PPAR␥ with L-764406 prevented binding of the [ 3 H]TZD, suggesting a covalent interaction with the receptor; in addition, structurally related analogues of L-764406, which would be predicted not to interact with PPAR␥ in a covalent fashion, did not displace [ 3 H]TZD binding to PPAR␥. Covalent binding of L-764406 was proven by an observed molecular weight shift of a tryptic PPAR␥ ligand binding domain (LBD) peptide by mass spectrometric analysis. A specific cysteine residue (Cys 313 in helix 3 of hPPAR␥2) was identified as the attachment site for this compound. In protease protection experiments, the liganded receptor adopted a typical agonist conformation. L-764406 exhibited partial agonist activity in cells expressing a chimeric receptor containing the PPAR␥ LBD and a cognate reporter gene and also induced the expression of the adipocyte-specific gene aP2 in 3T3-L1 cells. In contrast, L-764406 did not exhibit activity in cells transfected with chimeric receptors containing PPAR␣ or PPAR␦ LBDs. The partial agonist properties of L-764406 were also evident in a co-activator association assay, indicating that the increased transcription in cells was co-activator mediated. Thus, L-764406 is a novel non-TZD ligand for PPAR␥ and is also the first known partial agonist for this receptor. The results suggest a critical functional role for Cys 313 , and helix 3, in contributing to ligand binding and subsequent agonist-induced conformational changes.
Journal of Medicinal Chemistry, 2008
The peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors regulating glucose and lipid metabolism. The search for new PPAR ligands with reduced adverse effects with respect to the marketed antidiabetic agents thiazolidinediones (TZDs) and the dual-agonists glitazars is highly desired. We report the crystal structure and activity of the two enantiomeric forms of a clofibric acid analogue, respectively complexed with the ligand-binding domain (LBD) of PPARγ, and provide an explanation on a molecular basis for their different potency and efficacy against PPARγ. The more potent S-enantiomer is a dual PPARR/PPARγ agonist which presents a partial agonism profile against PPARγ. Docking of the S-enantiomer in the PPARR-LBD has been performed to explain its different subtype pharmacological profile. The hypothesis that partial agonists show differential stabilization of helix 3, when compared to full agonists, is also discussed. Moreover, the structure of the complex with the S-enantiomer reveals a new region of the PPARγ-LBD never sampled before by other ligands.