3r2a
From Proteopedia
Crystal structure of RXRalpha ligand-binding domain complexed with corepressor SMRT2 and antagonist rhein
Structural highlights
Function[RXRA_HUMAN] Receptor for retinoic acid. Retinoic acid receptors bind as heterodimers to their target response elements in response to their ligands, all-trans or 9-cis retinoic acid, and regulate gene expression in various biological processes. The RAR/RXR heterodimers bind to the retinoic acid response elements (RARE) composed of tandem 5'-AGGTCA-3' sites known as DR1-DR5. The high affinity ligand for RXRs is 9-cis retinoic acid. RXRA serves as a common heterodimeric partner for a number of nuclear receptors. The RXR/RAR heterodimers bind to the retinoic acid response elements (RARE) composed of tandem 5'-AGGTCA-3' sites known as DR1-DR5. In the absence of ligand, the RXR-RAR heterodimers associate with a multiprotein complex containing transcription corepressors that induce histone acetylation, chromatin condensation and transcriptional suppression. On ligand binding, the corepressors dissociate from the receptors and associate with the coactivators leading to transcriptional activation. The RXRA/PPARA heterodimer is required for PPARA transcriptional activity on fatty acid oxidation genes such as ACOX1 and the P450 system genes.[1] [2] [3] [4] [NCOR2_HUMAN] Transcriptional corepressor of NR4A2/NURR1 and acts through histone deacetylases (HDACs) to keep promoters of NR4A2/NURR1 target genes in a repressed deacetylated state (By similarity). Mediates the transcriptional repression activity of some nuclear receptors by promoting chromatin condensation, thus preventing access of the basal transcription. Isoform 1 and isoform 5 have different affinities for different nuclear receptors. Publication Abstract from PubMedRetinoic X receptor (RXR) is a master nuclear receptor in the processes of cell development and homeostasis. Unliganded RXR exists in an auto-repressed tetramer, and agonists can induce RXR dimerization and coactivator recruitment for activation. However, the molecular mechanisms involving the corepressor recruitment and antagonist-mediated repression of RXR are still elusive. Here we reported the crystal structure of RXRalpha ligand-binding domain (LBD) complexed with silencing mediator for retinoid and thyroid hormone receptors (SMRT) corepressor motif. As the first structural report on the unliganded nuclear receptor bound to the corepressor motif, RXRalphaLBD-SMRT exhibited a significant structural rearrangement, compared with the apo RXRalphaLBD tetramer. To further elucidate the molecular determinant for RXR repression by antagonist, we also determined the crystal structure of RXRalphaLBD-SMRT complexed with the identified antagonist rhein. In the structure, two rhein molecules and two SMRT peptides were in the RXRalphaLBD tetramer, different from the case in RXRalphaLBD-SMRT structure, where four SMRT peptides bound to RXR tetramer. It seemed that rhein binding has resulted in a displacement of SMRT motif for activation function-2 (AF-2) motif binding to the receptor. Combining our current work with the published results, structural superposition of RXRalphaLBDs in different states revealed that RXR used an overlapped binding site for coactivator, corepressor and AF-2 motif, while AF-2 motif adopted different conformations for agonist or antagonist interaction, and coactivator or corepressor recruitment. Taken together, we thus proposed a molecular model of RXR repression on the tetramer. Structural basis for retinoic X receptor repression on the tetramer.,Zhang H, Chen L, Chen J, Jiang H, Shen X J Biol Chem. 2011 May 24. PMID:21613212[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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