1. The Nuclear Xenobiotic Receptor CAR
Kelly Suino, Li Peng, Ross Reynolds, Yong Li, Ji-Young Cha, Joyce J. Repa, Steven A. Kliewer, H.Eric Xu 
Molecular Cell 
Volume 16, Issue 6, Pages (December 2004)
DOI: /j.molcel

2. Figure 1 Purification and Characterization of the CAR/RXR Heterodimer
(A) Purification of the CAR/RXR heterodimer. The proteins shown are crude extract (lane 1), the GST column elute (lane 2), the sample after thrombin digestion (lane 3), the nickel column flow through (lane 4), the Q column elute (lane 5), the purified GST-CAR LBD (lane 6), and the molecular weight markers (lane MW).
(B) Ligand-independent binding of the TIF2 coactivator motif to the purified CAR (red) or CAR/RXR (blue) as measured by α screen assays.
(C) Dose response curves of the CAR/RXR heterodimer (blue) and the CAR LBD (red) to TCPOBOP and androstanol.
(D) Binding affinities of the TIF2 motif to the CAR/RXR heterodimer (blue) and the CAR LBD in the absence (dash lines) or presence (solid lines) of TCPOBOP.
Molecular Cell  , DOI: ( /j.molcel )

3. Figure 2 Overall Structure of the CAR/RXR Heterodimer
(A) Ribbon representation of the CAR/RXR heterodimer in two views separated by 90°. RXR is colored in yellow and CAR in blue except for the AF2 helices, which are colored in red. The two TIF2 peptides are shown in purple. TCPOBOP and 9cRA are shown in space-filling representation with carbon, oxygen, nitrogen, and chloride depicted in green, red, blue, and yellow, respectively.
(B) The four layered helix sandwich of CAR LBD structure is shown in solid rendering (α helices in cylinders and β strands in yellow ribbons). TCPOBOP is shown in ball-and-stick form. Key secondary structural elements are annotated, including the linker helix Hx.
Molecular Cell  , DOI: ( /j.molcel )

4. Figure 3 Unique Features of the CAR/RXR Heterodimer Interface
(A) Structural comparison of the CAR/RXR and the PPARγ/RXR heterodimer complexes, where CAR/RXR is colored by blue and yellow and the PPARγ/RXR is colored by pink and purple, respectively. The CAR AF2 helix and the TIF2 that binds to CAR are colored green, and the PPARγ AF2 helix and the SRC-1 coactivator motif are shown in red. The superposition reveals that the RXR LBDs fit each other well in the two heterodimer complexes, but the CAR AF2 and the coactivator helix shift about 8 Å downward related to the corresponding PPARγ heterodimer. The differences between the CAR and the PPARγ LBDs are further illustrated in Figures 6B–6D.
(B) Superposition of the CAR/RXR and PPARγ/RXR heterodimers reveals a 16° rotation of the CAR LBD around the C terminus of H9 related to the PPARγ LBD.
(C) The core heterodimer interfaces showing the CAR H10 is shifted half helix turn (3 Å) related to the PPARγ.
(D) Hydrogen bonds between the CAR H7 and the RXR. The PPARγ H7 is shown in pink.
Molecular Cell  , DOI: ( /j.molcel )

5. Figure 4 The CAR LBD Structure
(A) Sequence alignment of mouse CAR and human CAR with PXR. The secondary structural elements are boxed and annotated below the sequences, and the residues that contact TCPOBOP are underlined. Stars note the residues that contribute the major pocket differences in the ligand binding pocket between the human and mouse CAR.
(B) Hydrogen bonds (arrows) between the CAR C-terminal carboxylate and residues of K205 and S337.
(C) Structural comparison of CAR with PXR, where the ligand binding pocket is shown in pink.
(D) Superposition of CAR with ERRγ, LRH-1, and agonist bound ERα. CAR is colored in blue except for the AF2 helix, which is in red. ERRγ, LRH-1, and ERα are colored in gold where key structural elements are annotated.
Molecular Cell  , DOI: ( /j.molcel )

6. Figure 5 Ligand Recognition by CAR
(A) Electron density map showing the TCPOBOP and the surrounding residues in CAR. The map is calculated with 2Fo−Fc coefficients and is contoured at one sigma.
(B) Schematic representation of CAR/TCPOBOP interactions. Hydrogen bonds and hydrophobic interactions are indicated by arrows and dashed lines. Residues that give a polar character to the surface of the pocket are colored in blue or red, and those resulting in a hydrophobic surface are shown in white.
(C) Effects of mutations in the pockets residues on the binding of the TIF2 coactivator motif in the presence or the absence of TCPOBOP. The fold of activation by TCPOBOP is indicated on the top of the bars.
(D) Pocket comparison between the mouse (pink) and the human (blue) CAR showing collision of M350 of human CAR with TCPOBOP.
Molecular Cell  , DOI: ( /j.molcel )

7. Figure 6 Binding of the TIF2 LXXLL Motif by CAR
(A) Structure of the TIF2 LXXLL motif (green) is shown on the surface of the CAR coactivator binding site, which is colored with atom types (carbon, white; sulfur, yellow; nitrogen, blue; and oxygen, red). The hydrogen bonds formed by the second charge clamp (between R+2 and E198 and between D+6 and R193) are indicated with dashed lines.
(B) Effects of the charge clamp mutations on the TIF2 binding to CAR in the presence or absence of TCPOBOP.
(C) Conservation of the second charge clamp residues in a subset of nuclear receptors as revealed by sequence alignment, where arrows indicate the amino acids that form the second charge clamp.
(D) Conservation of the R+2 and D+6 residues in the third LXXLL motif of the SRC1 coactivator family.
Molecular Cell  , DOI: ( /j.molcel )