Structural Basis for Hydroxycholesterols as Natural Ligands of Orphan Nuclear Receptor RORγ

The retinoic acid-related orphan receptor gamma (ROR gamma) has important roles in development and metabolic homeostasis. Although the biological functions of ROR gamma have been studied extensively, no ligands for ROR gamma have been identified, and no structure of ROR gamma has been reported. In this study, we showed that hydroxycholesterols promote the recruitment of coactivators by ROR gamma using biochemical assays. We also report the crystal structures of the ROR gamma ligand-binding domain bound with hydroxycholesterols. The structures reveal the binding modes of various hydroxycholesterols in the ROR gamma pocket, with the receptors all adopting the canonical active conformation. Mutations that disrupt the binding of hydroxycholesterols abolish the constitutive activity of ROR gamma. Our observations suggest an important role for the endogenous hydroxycholesterols in modulating ROR gamma 6-dependent biological processes. (Molecular Endocrinology 24: 923-929, 2010)