The ligand binding domain of Liver X receptors, a family of nuclear receptors of ligand-activated transcription factors.
The ligand binding domain of Liver X receptors: Liver X receptors (LXRs) belong to a family of nuclear receptors of ligand-activated transcription factors. LXRs operate as cholesterol sensors which protect from cholesterol overload by stimulating reverse cholesterol transport from peripheral tissues to the liver and its excretion in the bile. Oxidized cholesterol derivatives or oxysterols were identified as specific ligands for LXRs. Upon ligand binding a conformational change leads to recruitment of co-factors, which stimulates expression of target genes. Among the LXR target genes are several genes involved in cholesterol efflux from peripheral tissues such as the ATP-binding-cassette transporters ABCA1, ABCG1 and ApoE. There are two LXR isoforms in mammals, LXRalpha and LXRbeta. LXRalpha is expressed mainly in the liver, intestine, kidney, spleen, and adipose tissue, whereas LXRbeta is ubiquitously expressed at lower level. Both LXRalpha and LXRbeta function as heterodimers with the retinoid X receptor (RX R) which may be activated by either LXR ligands or 9-cis retinoic acid, a specific RXR ligand. The LXR/RXR complex binds to a liver X receptor response element (LXRE) in the promoter region of target genes. LXR has typical NR modular structure with a central well conserved DNA binding domain (DBD), a variable N-terminal domain, a flexible hinge and the ligand binding domain (LBD) at the C-terminal.