Elucidating the dynamic underpinnings of nuclear receptor biased agonism

Abstract

Approximately one out of six FDA-approved drugs target nuclear receptor proteins. This family of ligand-activated transcription factors has a highly dynamic activation mechanism that includes dimerization, ligand binding, and coregulator binding. After binding to coregulator proteins, nuclear receptors can specifically recruit different histone modifying proteins to thereby regulate gene expression. What is not fully understood about these proteins is how ligands can modulate the recruitment of specific coactivator proteins, known as biased agonism. Conventionally, it has been thought that helix 12 located on the C-terminus of the ligand binding domain acts as a crucial determinant for coregulator binding affinities. However, recent work has suggested that this mechanism is far more complex. In this project, we employed hydrogen deuterium exchange mass spectrometry to study the dynamics of the ligand binding domains of two nuclear receptors: peroxisome proliferator activator receptor gamma and farnesoid x receptor. Analyses were done in the presence of ligands and/or coregulators to elucidate changes in structural stability and dynamics of these proteins when in complex with various binding partners. This work has revealed that protein regions besides helix 12 proximal to the coregulator binding interface are involved in the biased agonism mechanism. By further understanding this mechanism, this work provides a significant opportunity for the development of new therapeutic agents with highly targeted effects.