The synthetic glucocorticoids (GCs) dexamethasone, mometasone furoate, and triamcinolone acetonide have been pharmaceutical mainstays to treat chronic inflammatory diseases. These drugs bind to the glucocorticoid receptor (GR), a ligand- activated transcription factor and member of the nuclear receptor superfamily. GR is widely recognized as a therapeutic target for its ability to counter pro-inflammatory signaling. Despite the popularity of GCs in the clinic, long-term use leads to numerous side effects, driving the need for new and improved drugs with less off-target pharmacology. X-ray crystal structures have played an important role in the drug-design process, permitting the characterization of robust structure-function relationships. However, steroid receptor ligand-binding domains (LBDs) are inherently unstable and their crystallization has required extensive mutagenesis to enhance expression and crystallization. Here, we utilize an ancestral variant of GR as a tool to generate a high- resolution crystal structure of GR in complex with the potent glucocorticoid triamcinolone acetonide (TA) and a fragment of the small heterodimer partner (SHP). Using structural analysis, molecular dynamics and biochemistry, we show that TA increases intramolecular contacts within the LBD to drive affinity and enhance stability of the receptor-ligand complex. These data support the emerging theme that ligand- induced receptor conformational dynamics at the mouth of the pocket play a major role in steroid receptor activation. This work also represents the first GR structure in complex with SHP, which has been suggested to play a role in modulating hepatic GR function.
- The American Society for Pharmacology and Experimental Therapeutics