Induced-fit refinement of the double histamine bound to Ra-HBP2. The induced-fit refinement 3D plot (A) shows the COM distance to Ra-HBP2 for the first (y-axis) and the second histamine (x-axis) compared to the binding energy (z-axis) of the second histamine. Panel B depicts the RMSD to the native Ra-HBP2 (PDB: 1QFT) for the first (y-axis) and the second histamine (x-axis) compared to the side chain perturbations for the functional residues reported in  (z-axis). The open and closed mouths are respectively shown in 180° turn (C) with the backbone superposition of the Ra-HBP2 original conformation (green; PDB: 1QFT) and a trajectory <1.5 Å RMSD for both histamines (cyan) after induced-fit refinement. Panel D is the same superposition (C) in 180° depicting specific residues within β-hairpin loops of both ends of the lipocalin barrel with large side chain perturbations as graphically shown along their trajectories (color-coded respectively to the structural representation). The COM for Ra-HBP2 is shown as a red sphere.