Phosphorylation regulated conformational diversity and topological dynamics of an intrinsically disordered nuclear receptor

Abstract

Site-specific phosphorylation of disordered proteins is often considered as a marker of protein activity, yet it is unclear how phosphorylation alters conformational dynamics of disordered protein chains, such as those in the nuclear receptor superfamily. In the case of disordered human glucocorticoid receptor N-terminal domain (GR NTD), a negatively charged region known as core activation function 1 (AF1c) features three phosphorylation sites, regulating its function and intracellular localization. Deletion of this sequence reduces GR transcriptional activation ability dramatically in cell experiments. By developing a circuit topology-based fold analysis approach, combined with atomistic simulations, we reveal that site-specific phosphorylation facilitates formation of non-local contacts, leading to the emergence of disordered compact topologies with significant entanglement, which are distinct from solvent exposed topologies. While we observe that the topological buildup of solvent-exposed states is similar in different phosphovariants, it depends on the exact phosphorylation site for the disordered compact states. This study thus reveals the complex regulatory role of the GR phosphorylation and introduces a unique analysis framework that can be broadly applied to studying topological dynamics of disordered proteins.