The ligand binding domain of xenobiotic receptors:pregnane X receptor and constitutive androstane receptor
The ligand binding domain of xenobiotic receptors: This xenobiotic receptor family includes pregnane X receptor (PXR), constitutive androstane receptor (CAR) and other related nuclear receptors. They function as sensors of toxic byproducts of cell metabolism and of exogenous chemicals, to facilitate their elimination. The nuclear receptor pregnane X receptor (PXR) is a ligand-regulated transcription factor that responds to a diverse array of chemically distinct ligands, including many endogenous compounds and clinical drugs. The ligand binding domain of PXR shows remarkable flexibility to accommodate both large and small molecules. PXR functions as a heterodimer with retinoic X receptor-alpha (RXRa) and binds to a variety of response elements in the promoter regions of a diverse set of target genes involved in the metabolism, transport, and elimination of these molecules from the cell. Constitutive androstane receptor (CAR) is a closest mammalian relative of PXR, which has also been proposed to function as a xenosensor. CAR is activated by some of the same ligands as PXR and regulates a subset of common genes. The sequence homology and functional similarity suggests that the CAR gene arose from a duplication of an ancestral PXR gene. Like other nuclear receptors, xenobiotic receptors have a central well conserved DNA binding domain (DBD), a variable N-terminal domain, a flexible hinge and a C-terminal ligand binding domain (LBD).