Volume 16, Issue 6, Pages 919-928 (December 2004) A Structural Basis for Constitutive Activity in the Human CAR/RXRα Heterodimer  Robert X. Xu, Millard H. Lambert, Bruce B. Wisely, Erin N. Warren, Emily E. Weinert, Gregory M. Waitt, Jon D. Williams, Jon L. Collins, Linda B. Moore, Timothy M. Willson, John T. Moore  Molecular Cell  Volume 16, Issue 6, Pages 919-928 (December 2004) DOI: 10.1016/j.molcel.2004.11.042

Figure 1 CAR/RXRα Heterodimer Structure in the Complex with CITCO, Fatty Acid, and SRC-1 Peptides (A) Ribbon diagram of the human CAR/RXRα heterodimer complex with two SRC-1 peptides. CITCO is docked in the CAR ligand binding site as described in the text. The SRC-1 peptides are in magenta. The 310 helixes of CAR and RXRα are colored blue. The AF2 helices are colored in red. Helix X (H-X) is colored in gold. H7 and H10 are annotated. CITCO in CAR and the endogenous fatty acid in RXRα are shown in space-filling representation colored by atom type: oxygen is red, nitrogen is blue, sulfur is yellow, and carbon is green. (B) 90° rotation of the heterodimer viewed from the bottom of H10. Molecular Cell 2004 16, 919-928DOI: (10.1016/j.molcel.2004.11.042)

Figure 2 Structural Features of the CAR/RXRα Heterodimer (A) Ribbon diagrams of the C terminus of CAR (blue), VDR (yellow), and PXR (green). In CAR, Helix X is colored in gold, and the AF2 helix is in red. The SRC-1 peptide is colored magenta. K195 from CAR that interacts with the C-terminal carboxylate is shown in sick representation colored by atom type. (B) Ribbon diagram of CAR with Helix X in gold and the AF2 helix in red. Helix H3 has been deleted for clarity. The four barrier residues are shown with carbon atoms colored yellow. Key residues from Helix X and the AF2 helix that sit on the barrier are colored with gold and red, respectively. CITCO is shown in space-filling representation colored by atom type. (C) Ribbon diagrams CAR (blue) and PPARγ (green) showing the difference in the bowing of H7. The linear H7 in CAR is shown in dark blue. (D) Ribbon diagram showing the interaction of T462 from RXRa with H332 for CAR H10 and N235 from H10. CAR is colored in blue. RXRα is colored in yellow with the AF2 C-terminal extension in red. Molecular Cell 2004 16, 919-928DOI: (10.1016/j.molcel.2004.11.042)

Figure 3 Electron Density in the CAR and RXR Ligand Binding Pockets (A) The 2fo−fc map of the electron density for 5β-pregnanedione in the pocket of CAR. The map is contoured at 1.25 σ. 5β-pregnanedione is shown in stick representation colored by atom type. (B) The 2fo−fc map electron density map calculated from a refined CAR/RXR heterodimer structure without CITCO. The map is contoured at 1.00 σ. The docked CITCO model is shown in stick representation colored by atom type. The carbon atoms of the two CITCO molecules are in white and pink. (C) The 2fo−fc map of the fatty acid electron density in the pocket of RXRα. The map is contoured at 1.250 σ. The first 15 carbon atoms of the fatty acid are shown in stick representation colored in green. The structure is overlaid with 9cRA bound in RXRα pocket from the PPARγ/RXRα heterodimer (Gampe et al., 2000) shown in stick representation with the carbon atoms colored in white. Molecular Cell 2004 16, 919-928DOI: (10.1016/j.molcel.2004.11.042)

Figure 4 Structural and Mutational Analysis of CAR Ligand Binding (A) 5β-pregnanedione (carbon atoms colored cyan) in the binding pocket. The figure shows residues that are within 6 Å distance from the steroid, colored by atom type. Carbon atoms of the protein are colored green, oxygen atoms are red, and nitrogen atoms are blue. The four amino acids that comprise the barrier are colored with their carbon atoms in yellow. L343 from the AF2 helix is colored red. The dot surface represents the ligand binding site. (B) Two conformations of CITCO (carbon atoms colored cyan and pink) docked in the active site of CAR. The color scheme is as in Figure 3A. (C) Transactivation data from the wild-type or mutant CAR full-length receptors. Compounds were tested at 3 μM. Molecular Cell 2004 16, 919-928DOI: (10.1016/j.molcel.2004.11.042)