The long-term objective of this study is to reveal the structural mechanisms of hormone actions mediated by the glucocorticoid receptor (GR) and the mineralococorticoid receptor (MR). GR and MR are members of the steroid hormone receptor family that regulate broad spectrum of human physiology ranging from immune/inflammatory responses to metabolic homeostasis and control of blood pressure. Importantly, both GR and MR are well-established drug targets, with a number of their ligands currently being used to treat diverse diseases including inflammation and hypertension. GR and MR mediate their actions through hormone binding to their C-terminal ligand-binding domain (LBD) and promoter binding of target genes to their middle DMA-binding domain (DBD). Both receptors also contain a potent N-terminal activation domain (AF-1). Until recently, only structures of the isolated DBD or the isolated GR LBD with a single agonist (dexamethasone) had been solved. Clearly, this limited amount of structural information is a serious deficiency considering the importance of GR and MR in normal physiology and in disease. In this study, we propose to fill in that knowledge gap by solving the crystal structures of various GR and MR complexes.
Our specific aims are focused on crystallization and structural determination of 1) the MR LBD, 2) the GR LBD in complex with cortivazol, a potent anti-inflammatory ligand that binds to GR with 40-fold higher affinity than dexamethasone, 3) a MR DBD-LBD fragment bound to the MR consensus DNA site, and 4) the GR AF-1-DBD/DNA complex that contains the GR AF-1 domain and its DBD. The hypothesis for our specific aims is that the molecular interactions (protein-protein, protein-DNA, and protein-hormone) observed in these crystal structures will be crucial for mechanistic understanding of the hormone actions of GR and MR. After structural determination, we will identify key structural elements by scrutinizing and analyzing the structures, and we will collaborate closely with Stoney Simons (NIDDK), Brad Thompson, and Raj Kumar (UTMB, Galveston), in site-directed mutagenesis and cell-based transcriptional assays to assess the functional significance of the key features identified. Significance: The structural information generated in this application will significantly enhance our understanding of the molecular mechanisms of hormone actions by GR and MR, and should serve as rational templates for drug discovery that targets these 2 receptors for the treatment of asthma, hypertension, and heart disease.
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