title: Agonist-dependent and agonist-independent transactivations of the human constitutive androstane receptor are modulated by specific amino acid pairs.
abstract: The constitutive androstane receptor (CAR) is an interesting member of the nuclear receptor superfamily because of its exceptionally high constitutive activity due to ligand-independent interaction of the ligand-binding domain with co-activator proteins. This study compares the agonist-dependent and agonist-independent activities of human CAR with those of mouse CAR and the vitamin D receptor and demonstrates that the constitutive activity of CAR is mediated by at least three contacts between the amino acids of helix 12, partner amino acids in helices 4 and 11, and a charge clamp between helices 12 and 3. The stabilization of helix 12 by a contact between its C terminus and the lysine of helix 4 has the same impact in human and mouse CARs. In addition, the charge clamp between the glutamate in helix 12 and the lysine in helix 3 is also important for the constitutive activity of both receptor orthologs but less critical for the agonist-dependent stabilization of their respective helices 12. Interestingly, Cys-357 in mouse CAR has significantly more impact on the stabilization of helix 12 than does the orthologous position Cys-347 in human CAR. This deficit appears to be compensated by a more dominant role of Ile-330 in human CAR over Leu-340 in mouse CAR because it is more efficient than Cys-347 in controlling the flexibility of helix 12 in the presence of an agonist. The constitutive activity of other members of the nuclear receptor superfamily could be explained by a homologous hydrophobic interaction between large, non-polar amino acids of helices 11 and 12.
authors.affiliation: Department of Biochemistry, University of Kuopio, FIN-70211 Kuopio, Finland.
authors.forename: Christian
authors.initials: C
authors.lastname: Frank
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Molnár
authors.forename: Merja
authors.initials: M
authors.lastname: Matilainen
authors.forename: Harri
authors.initials: H
authors.lastname: Lempiäinen
authors.forename: Carsten
authors.initials: C
authors.lastname: Carlberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001943:Breast Neoplasms; D000090702:Constitutive Androstane Receptor; D003545:Cysteine; D019281:Dimerization; D004355:Drug Stability; D018698:Glutamic Acid; D006801:Humans; D007532:Isoleucine; D007930:Leucine; D008239:Lysine; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D018167:Receptors, Calcitriol / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D016415:Sequence Alignment; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000090702:Constitutive Androstane Receptor; D018167:Receptors, Calcitriol; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D007532:Isoleucine; D018698:Glutamic Acid; D007930:Leucine; D008239:Lysine; D003545:Cysteine