ANS interaction sites on hFABP3. (a) A cartoon representation of the hFABP3–ANS complex structure. ANS is represented as green sticks. The solvent molecules are represented as red spheres. (b) The Fobs − Fcalc electron density omit map of ANS. ANS (green) is located in the binding cavity of hFABP3. The electron density is calculated at 2.15 Å and contoured at 2.5σ. The O, N and S atoms are shown in red, blue and yellow, respectively. (c) Principal interaction sites of hFABP3 are shown schematically. One of the ANS sulfonate O atoms forms hydrogen bonds with the hydroxyl group of Tyr128 as well as the guanidium N atom of Arg126 via water molecules. Furthermore, the rest of the O atoms form hydrogen bonds with the guanidium N atom of Arg106 via a water molecule. Hydrogen-bonding interactions are shown as green dashed lines (lengths in Å). The schematic was drawn using the program LIGPLOT.