The binding free energy along the reaction path at different ionic strengths: 0.1 M (red), 0.15 M (green), 0.2 M (blue), 0.3 M (magenta), 0.4 M (cyan), and 0.5 M (black). (Inset) Complex configuration at dave = 26.0 Å (top), 13.0 Å (middle), and 8.5 Å (bottom). The protein structure in the reference is in gray.