3D structures and ligand specificities of nuclear xenobiotic receptors CAR, PXR and VDR

The nuclear receptors constitutive androstane receptor (CAR), pregnane X receptor (PXR) and vitamin D receptor (VDR) control a large array of genes that code for important proteins in humans including metabolic enzymes and transporters. 3D structures for the ligand-binding domain (LBD) of these receptors are abundantly available, providing valuable insights into the ligand-binding specificity as well as the activation mechanisms. The ligand-binding site of PXR is large and flexible, whereas those of CAR and VDR are compact and rigid, respectively. In general, the ligand profiles of the receptors are in agreement with the LBD structures. The crystal structures have greatly helped us to understand the promiscuity and/or specificity of CAR, PXR and VDR.

► 3D structures provide deep insight into the receptor action and ligand recognition. ► PXR ligand-binding site is large and incredibly flexible that binds bulky ligands. ► VDR binding site is rigid; the ligands need to adapt themself for proper binding. ► CAR binding site is compact, and is isolated from the activation function 2 helix. ► The ligand profiles of the NRs are well correlated with the binding site features.