Effects of Site‐specific Phosphorylation on the Structure and Functions of the Intrinsically Disordered N‐terminal Activation Function (AF1) Domain of the Glucocorticoid Receptor

Abstract

In eukaryotic cells, phosphorylation regulates protein structure and functions. The glucocorticoid receptor (GR) is a phosphoprotein with all the conserved sites located within its AF1 activation domain. Structure of AF1 has been difficult to determine because it exists as an intrinsically disordered (ID) protein, frequently found in transcription factors. ID regions are disproportionately higher in cell signaling proteins and are predicted to have much higher frequency of phosphorylation sites than ordered regions, suggesting an important role in their regulatory capacity. It has been suggested that phosphorylation plays an important role in the regulation of GR activity. In this study, we found that ID AF1 adopts a functionally folded conformation due to phosphorylation of S211 by p38 MAPK. Further, this induced secondary/tertiary structure in AF1 specifically facilitates its interactions with critical coregulatory proteins, and subsequent AF1‐mediated transcriptional activity of the GR. Together, we propose that under physiological conditions, site‐specific phosphorylation plays a crucial role in allowing AF1 to adopt functionally active conformation(s), which facilitates AF1’s interactions with specific coregulatory proteins, and possibly additional modulations that form the basis for the multi‐protein assemblies involved in GR‐mediated regulation of transcription.