Fig. S1.

Holo-hCA II active site. Comparisons of (A) holo-hCA II (yellow; 0 s) CO₂-bound and (B) the previously reported CO₂-bound (cyan; PDB ID code 3D92) structures. Superposed electron density map from A (0 s) onto holo-hCA II CO₂ free in C (magenta; PDB ID code 3KS3) and D (green; PDB ID code 2ILI). The 2F_o-F_c (blue) and F_o-F_c (green) electron density maps are contoured at 2.0σ and 4.0σ, respectively. The 2F_o-F_c maps for waters and CO₂ are highlighted in pink for clarity. Note that the electron density modeled as glycerol in 3D92(B) is W2 and W3b in the CO₂-free holo-hCA IIs (C and D). Also, observe that W_I in the CO₂-bound hCA II (A and B) is not observed in the CO₂-free holo-hCA II and instead, that W1 is positioned in the solvent network (C and D).