Peroxisome proliferator-activated receptor gamma (PPAR?) is a nuclear receptor transcription factor that regulates cellular differentiation, adipogenesis, and insulin resistance by recruiting transcriptional coregulator proteins (corepressor and coactivator proteins) to target gene promoters in a ligand-dependent manner. Structure-function approaches have defined how the transcriptionally active structural conformation and coactivator-selective functions of PPAR? are influenced by agonist ligands. However, little is known about the transcriptionally repressive conformation and corepressor-selective functions of PPAR?. Our long-term goal is to close this knowledge gap by defining how different pharmacological PPAR? ligands influence the structure and function of PPAR? between transcriptionally active and repressive states. In preliminary studies, we solved crystal structures of the PPAR? ligand-binding domain (LBD) in a transcriptionally repressive state using a unique corepressor-selective ligand, revealing a unique structural conformation that we have started to validate using solution NMR methods. In this project, we will use mechanistic studies to define how small molecule ligands impact PPAR? activation and repression on the molecular, structural, and cellular levels. Successful outcomes from our studies will define the activity-dependent conformational ensemble of the PPAR? LBD, develop ligands with enhanced corepressor-selective activity, and determine the molecular mechanisms by which corepressor-selective repressive ligands modulate PPAR? cellular functions.