The binding of CAPS to APAH mimics the binding of the tetrahedral intermediate. (A) Simulated annealing omit map of CAPS contoured at 4 σ. Metal coordination, hydrogen bond, and cation-π interactions are shown as black, orange, and green dashed lines, respectively. Atoms are color-coded as follows: C = yellow (APAH) or gray (CAPS); N = blue; O = red; S = orange; Zn2+ = magenta sphere. (B) The sulfonate group of CAPS mimics the tetrahedral intermediate that forms during APAH hydrolysis reaction (C).