PDBsum entry 1xnx

Ligand receptor/transcription regulation

PDB id: 1xnx

Contents

Protein chains

232 a.a. *

Ligands

ATE ×2

Waters ×33

* Residue conservation analysis

PDB id:

1xnx

Name:

Ligand receptor/transcription regulation

Title:

Crystal structure of constitutive androstane receptor

Structure:

Constitutive androstane receptor. Chain: a, b. Synonym: orphan nuclear receptor nr1i3. Car. Engineered: yes

Source:

Mus musculus. House mouse. Organism_taxid: 10090. Gene: nr1i3, car. Expressed in: escherichia coli. Expression_system_taxid: 562.

Resolution:

2.90Å R-factor: 0.229 R-free: 0.288

Authors:

E.Fernandez

Key ref:

L.Shan et al. (2004). Structure of the murine constitutive androstane receptor complexed to androstenol: a molecular basis for inverse agonism. Mol Cell, 16, 907-917. PubMed id: 15610734 DOI: 10.1016/j.molcel.2004.11.037

Date:

05-Oct-04 Release date: 04-Jan-05

Protein chains

O35627  (NR1I3_MOUSE) -  Nuclear receptor subfamily 1 group I member 3 from Mus musculus

Seq: 358 a.a.

Struc: 232 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

DOI no: 10.1016/j.molcel.2004.11.037

Mol Cell 16:907-917 (2004)

PubMed id: 15610734

Structure of the murine constitutive androstane receptor complexed to androstenol: a molecular basis for inverse agonism.

L.Shan, J.Vincent, J.S.Brunzelle, I.Dussault, M.Lin, I.Ianculescu, M.A.Sherman, B.M.Forman, E.J.Fernandez.

ABSTRACT

The nuclear receptor CAR is a xenobiotic responsive transcription factor that plays a central role in the clearance of drugs and bilirubin while promoting cocaine and acetaminophen toxicity. In addition, CAR has established a "reverse" paradigm of nuclear receptor action where the receptor is active in the absence of ligand and inactive when bound to inverse agonists. We now report the crystal structure of murine CAR bound to the inverse agonist androstenol. Androstenol binds within the ligand binding pocket, but unlike many nuclear receptor ligands, it makes no contacts with helix H12/AF2. The transition from constitutive to basal activity (androstenol bound) appears to be associated with a ligand-induced kink between helices H10 and H11. This disrupts the previously predicted salt bridge that locks H12 in the transcriptionally active conformation. This mechanism of inverse agonism is distinct from traditional nuclear receptor antagonists thereby offering a new approach to receptor modulation.

Selected figure(s)

Figure 1.
Figure 1. Structure of mCAR LBD/Androstenol Complex(A and B) Ribbon representation of each CAR molecule within the asymmetric unit. The arrow indicates the region of missing density between helices H11 and H12 in molecule B. The bound ligand is also displayed in each molecule as ball-and-stick representations.(C) F[o]-F[c] omit map contoured at 5σ for androstenol within the binding pocket. The model is superimposed on the electron density, and the androstenol is colored blue (carbon) and red (hydroxyl).(D) Electrostatic surface representation of the ligand binding pocket. Androstenol is shown in black (carbon) and red (hydroxyl).

Figure 4.
Figure 4. Model for Androstenol-Induced Repression of CAR(A) A stereo model to show that when bound to androstenol, the CAR helix H11 (purple) adopts a conformation that is similar to apo inactive RXR (gray), which is in contrast to the fused H10-H11 helix in the agonist bound active nuclear receptor conformations such as in PXR (blue).(B) A Glu339-Gln245 backbone amide hydrogen bond acts as a “pin” about which helix H11 can twist toward the ligand binding pocket in CAR (purple). This interaction is conserved in most nuclear receptors even when in the active state conformation as in the VDR structure (cyan, Gln400). Residues in parentheses are from VDR.(C) The Glu339-Gln245 backbone amide hydrogen bond is important for maintaining the integrity of the ligand binding pocket. Relative to wild-type CAR, dose response experiments demonstrate that the E339A mutant displays a 10-fold higher EC[50] for androstenol (RE2×2-TK-Luc reporter construct).(D) A conceptual model of CAR active-to-inactive state transition. Apo CAR is in green showing the predicted K205-C terminus interaction that stabilizes AF2 in the active conformation. Binding to androstenol leads to a movement (double-headed arrow) of helix H11 toward the binding pocket, generation of the H10-H11 kink, and dissociation of H12 from the body of the protein as in the CAR/androstenol structure presented here.

The above figures are reprinted by permission from Cell Press: Mol Cell (2004, 16, 907-917) copyright 2004.

Figures were selected by an automated process.