Fig. 5
From: Molecular tuning of farnesoid X receptor partial agonism
NMR studies on the FXR activation mechanism. a Amino acid sequence of co-repressor (NCoR) and the co-activator (NCoA) with 15N/13C-isotpically enriched amino acids highlighted with larger font. A stick model of leucine with its Hβ highlighted. The inset shows the Hβ-region of 1H, 13C-HSQC spectra of the labelled peptides. The chemical shifts for the NCoA and NCoR are not overlapping and are easily distinguishable. b Schematic representation of the typical behaviour of an LBD in response to ligand-dependent activation and c resulting changes in the NMR signal (Hβ of leucine) of the co-repressor (NCoR) at different points of interaction. Disappearance of NMR signals upon binding to FXR, partial reappearing (release) upon addition of agonist and further reappearance upon addition of NCoA indicating complete release of NCoR. d Monitoring of the Hβ-signal of leucine in NCoR in response to addition of FXR, followed by addition of ligand (e–i) and the co-activator peptide: The Hβ signals of the co-repressor (d) are severely broadened upon addition of FXR, indicating binding. Upon addition of an agonists (e–g), an increase in signal intensity is observed indicating that agonist binding induces partial release of NCoR (e–g, left spectra). Further, upon addition of the co-activator peptide, the intensity of the NCoR signals further increases and the signals of NCoA disappear (blue circled region), indicating the complete release of the co-repressor and binding of NCoA to the FXR-agonist complex (e–g, right spectrum). The bar graphs adjacent to the spectra represent the relative populations of the released NCoR/NCoA peptides upon binding of the ligand. Populations of each reporter signal were determined from their intensities as P[(CDCANCoR) = 100∙INCoR/(INCoR + INCoR)] and vice versa. The spectra obtained in the presence of partial agonists (h, i) show marginal increase in the intensity of the repressor signals and minor line broadening for the signals of the activator, indicating that both co-repressor and the co-activator bind. This is also reflected by the relative populations of the released NCoR/NCoA peptides. Antagonist guggulsterone, in contrast, in this setting induces full binding of NCoR peptide with no recruitment of NCoA peptide (see Supplementary Fig. 7)
