title: Molecular determinants of the balance between co-repressor and co-activator recruitment to the retinoic acid receptor.
abstract: The repressive and activating states of nuclear hormone receptors are achieved through the recruitment of cofactor proteins. The binding of co-repressors and co-activators is believed to be mutually exclusive and principally regulated by ligand binding. To understand the molecular determinants of the switch induced by ligand in the retinoic acid receptor and in particular the intrinsic role of the ligand binding domain (LBD) in cofactor binding and release, we carried out extensive mutational analysis of surface residues of the LBD. As seen previously we found that co-repressor and co-activator molecules bind to overlapping docking sites on the surface of the retinoic acid receptor alpha LBD. Perturbation of this surface impaired both co-activator and co-repressor association resulting in a transcriptionally inert receptor. Unexpectedly mutation of two residues, Trp-225 and Ala-392, which lie outside the docking site, had opposite effects on co-activator and co-repressor binding. W225A was a constitutive repressor that failed to bind co-activator and exhibited an increased, and ligand-insensitive, interaction with co-repressor. A392R, on the other hand, had reduced affinity for co-repressors and increased affinity for co-activators and behaved as a constitutive, but still ligand-inducible, activator. Analysis of known structures showed that these mutations lie in the proximity of helix 12 (H12), and their effects are likely to be the result of perturbations in the behavior of H12. These data suggest that residues in the close vicinity of H12 regulate cofactor affinity and determine the basal activity of receptors.
authors.affiliation: Department of Biochemistry and Molecular Biology, Research Center for Molecular Medicine, University of Debrecen, Medical and Health Science Center, Nagyerdei krt. 98, Debrecen H-4012, Hungary.
authors.forename: Szilvia
authors.initials: S
authors.lastname: Benko
authors.forename: James D
authors.initials: JD
authors.lastname: Love
authors.forename: Marta
authors.initials: M
authors.lastname: Beládi
authors.forename: John W R
authors.initials: JW
authors.lastname: Schwabe
authors.forename: Laszlo
authors.initials: L
authors.lastname: Nagy
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D004252:DNA Mutational Analysis; D005982:Glutathione Transferase / Q000378:metabolism; D000882:Haplorhini; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014162:Transfection; D014364:Tryptophan / Q000737:chemistry
chemical_list: D008024:Ligands; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D014364:Tryptophan; D008156:Luciferases; D005982:Glutathione Transferase; D000409:Alanine