(A-C) The sigmaA-weighted 2Fo-Fc electron density map contoured at 1σ within the sterol binding pocket is shown in gray mesh for the apoNPC1(NTD) (A), the cholesterol-bound (B), and 25-HC-bound (C) forms. The binding pocket is essentially identical in apoNPC1(NTD) and the sterol bound forms. The binding pocket of apoNPC1(NTD) is occupied by 2 glycerol and 3 water molecules. NPC1(NTD) is colored gray, bound ligands are colored green, and water molecules are shown as red spheres.
(D) The internal surface of the binding pocket is shown in gray. Bound 25-HC is shown in green.