Biostructural studies on PPAR nuclear receptors

The peroxisome proliferator-activated receptors (PPARs) represent a family of nuclear receptors that function as ligand-activated transcription factors, regulating genes involved in cell differentiation and various metabolic processes, especially lipid and glucose homeostasis. The PPAR family comprises three isoforms: PPARα, PPARβ/δ and PPARγ, with different tissue distribution, ligand specificitiy and physiological role. Because of their wide range of actions on glucose homeostasis, lipid metabolism and vascular inflammation, PPARs represent promising targets for the development of new drugs for the treatment of metabolic disorders such as type 2 diabetes mellitus (T2DM), dyslipidemia and atherosclerosis. Among all the subtypes, despite the undesiderable side effects associated to the drug treatment, PPARγ is still the most widely studied for its crucial role in the complex cross-talk between metabolically active tissues essential for energy balance. Then, new combination strategies using dual or pan agonists, as well as selective modulators, are currently in development. This study is aimed to understand in deep the dynamic personality of the nuclear receptors PPAR in complex with both natural and synthetic ligands that, interacting with different regions of the LBD, confer a differentiated biological response in cellular and animal models. PPARs could be then described as a ‘functionally pluripotent’ proteins being their activity mediated by ligands that, causing the functional site to adopt an active/inactive conformations, activate different structural and biological pathways depending on the co-activator/co-repressor recruited. Through a structural approach we propose to get more insights on how the biological response is variably affected by ligands depending on their binding mode and even the mutation of a single residue responsible for a structural destabilization of the LBD could be associated to rare genetic disorder. The understanding of such a mechanism required the use of more than one biophysical technology. X-ray diffraction was used as the main approach to investigate the binding mode of the selected ligands. In addition, the binding has been also characterized using other biophysical techniques such as Isotermal Titration Calorimetry (ITC) and Surface Plasmon Resonance (SPR) to obtain thermodynamic and kinetic parameters of the binding.