Thermodynamic Characterization of the Interaction between CAR-RXR and SRC-1 Peptide by Isothermal Titration Calorimetry
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- 作者：Edward Wright ; Jeremy Vincent ; Elias J. Fernandez
- 刊名：Biochemistry
- 出版年：2007
- 出版时间：January 23, 2007
- 年：2007
- 卷：46
- 期：3
- 页码：862 - 870
- 全文大小：124K
- 年卷期：v.46,no.3(January 23, 2007)
- ISSN：1520-4995
文摘
The constitutive androstane receptor (CAR) enhances transcription of specific target genesthat regulate several metabolic pathways. CAR functions as an obligate heterodimer (CAR-RXR) withthe retinoid X receptor (RXR). Also part of the active receptor complex is the steroid receptor coactivator-1(SRC-1) which interacts with the receptor complex via specific receptor interaction domains (RIDs). Apeptide derived from SRC-1 RID2 is used to study the thermodynamic properties of the interaction withthe CAR-RXR ligand binding domain (LBD) complex. In the absence of ligands for both CAR andRXR, binding of coactivator peptide to the CAR-RXR heterodimer is characterized by a favorable enthalpychange and an unfavorable entropy change. The addition of the CAR agonist, TCPOBOP, increases theaffinity for coactivator by decreasing the unfavorable entropy and increasing the favorable intrinsic enthalpyof the interaction. The RXR ligand, 9-cis-RA, generates a second SRC-1 site and increases the affinity byimproving the entropic component of binding. There is an additional increase in affinity for one of thetwo sites in the presence of both ligands. The change in heat capacity (
Cp) is also investigated. A 2-folddifference in Cp is observed between liganded and unliganded CAR-RXR. The observed thermodynamicparameters for binding of SRC-1 peptide to liganded and apo CAR-RXR as well as the difference in theCp data provide evidence that the apo CAR-RXR heterodimer is conformationally mobile. The morefavorable enthalpic contribution for TCPOBOP-bound CAR-RXR indicates that preformation of thebinding site improves the complementarity of the coactivator-receptor interaction.
Cp) is also investigated. A 2-folddifference in Cp is observed between liganded and unliganded CAR-RXR. The observed thermodynamicparameters for binding of SRC-1 peptide to liganded and apo CAR-RXR as well as the difference in theCp data provide evidence that the apo CAR-RXR heterodimer is conformationally mobile. The morefavorable enthalpic contribution for TCPOBOP-bound CAR-RXR indicates that preformation of thebinding site improves the complementarity of the coactivator-receptor interaction.