Figure 1.

(A) Overall structure of RePON1 in complex with the inhibitor 2-hydroxyquinoline (2HQ) obtained at pH 6.5 (PDB ID 3SRG).⁷ Here the flexible loop (residues 70–81) is highlighted in red, the three surface helices are highlighted in salmon, the Ca²⁺ ions are highlighted in green, and 2HQ is highlighted in orange. (B) Close-up of the active site tunnel leading from the catalytic Ca²⁺ to the surface helix H2. Key residues involved in this network as well as the corresponding hydrogen-bonding distances in the 3SRG crystal structure are shown.