Single-molecule force spectroscopy reveals folding steps associated with hormone binding and activation of the glucocorticoid receptor

Significance The glucocorticoid receptor (GR) is an important signaling protein and a prominent drug target. Cortisone, one of the drugs directed against the GR, is among the most prescribed drugs worldwide. Hormone binding leads to activation of the receptor, which is then transported into the nucleus, affecting gene transcription. Despite its importance, little is known about the structural prerequisites of hormone binding and the associated conformational changes. We used a mechanical single-molecule method that allowed us to observe in detail the steps of folding and hormone binding of GR. We identify a structural element that opens and closes upon hormone binding. Our results form the basis for understanding GR activation and its regulation by chaperone proteins.