Figure 3. FXR Lys insertion mutation abrogates consensus IR-1 FXR binding and transactivation.

(a) The highly conserved zinc-finger domain of the human FXR protein. The residue of nonsense mutation found in family 1 is indicated with a green arrow. The location of the in-frame Lys 140 insertion found in family 2 is indicated with a red arrow. ‘Zn' stands for zinc ions. Cysteine residues that directly interact with zinc ions are in red. (b) Comparison of predicted structures of DBD. Predicted structures of wild-type FXR and FXR mutant with in-frame insertion based on the structure of EcR/RXR DBD in complex with IR-1 (PBD 1R0N). RXR is rendered in grey, EcR in orange, wild-type hFXR in cyan, hFXR mutant in purple and zinc ions are in green. The inserted lysine residue is in red with side chain shown. (c) Electrophoretic mobility-shift assay performed with a consensus FXRE or the FXR-binding region in mouse SHP promoter and wild-type or Lys insertion mutant FXR and RXR as indicated. (d) Relative luciferase expression directed by a reporter containing three copies of a consensus in response to wild-type and mutant FXR proteins in the presence or absence of the synthetic FXR agonist GW4064. Repeated three times (*P, 0.01 by t-test, error bars s.d.). FXRE, FXR-binding element.