DNA-binding domain of Liver X receptors (LXRs) family is composed of two C4-type zinc fingers
DNA-binding domain of Liver X receptors (LXRs) family is composed of two C4-type zinc fingers. Each zinc finger contains a group of four Cys residues which co-ordinates a single zinc atom. LXR interacts with specific DNA sites upstream of the target gene and modulates the rate of transcriptional initiation. LXR operates as cholesterol sensor which protects cells 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. LXR functions as a heterodimer with the retinoid X receptor (RXR) which may be activated by either LXR agonist 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. The ideal LXRE sequence is a direct repeat-4 (DR-4) DNA fragment consisting of two AGGTCA hexameric half-sites separated by a 4-nucleotide spacer. 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.