Figure 2. 7α-OH steroids are bound in the tunnel of ATX.
(a) A zoom-in to the model with difference density (mFo−DFc) shown as a green wireframe model before any ligand or water placement contoured at 3.5 RMS highlighting the unexplained density in the tunnel. (b) The model is rotated about 90° along the vertical display axis to show the same difference density map. (c) The model is shown in the same orientation as before after including a sterol molecule in the refinement; the resulting 2mFo−DFc map is shown in blue at 1.2 RMS and the difference map in green still indicates a missing atom. (d) The electron density maps after full refinement including the 7α-hydroxycholesterol molecule; all difference density peaks have disappeared. (e) The molecular structure of 7α-hydroxycholesterol showing all atom and ring names.