The PXR crystal structure: the end of the beginning

The pregnane X receptor (PXR) has a key role in the regulation of both drug metabolism and drug efflux by activating the expression of genes encoding cytochrome P450 enzymes and drug efflux transporters, respectively. Thus, coadministration of a PXR ligand and drugs handled by such enzymes or transporters leads to drug interactions. The need to identify drugs in development with the least potential to cause adverse drug interactions has led to the recent solving of the crystal structure of the human PXR ligand binding domain.