Figure 4. Crystal structures of PA_N ^ΔLoop bound to compounds 1–6 (A–F, respectively).

PA_N ^ΔLoop is shown as gray cartoon. Compounds are shown as ball-and-stick models and are colored yellow (carbon), blue (nitrogen), red (oxygen), and orange (chlorine). Manganese ions (Mn1 and Mn2) are shown as green spheres. The carbon atoms of key active site residues are colored magenta, and the carbon atoms of other residues interacting with the compound or discussed in the text are colored cyan. An ordered water molecule (H₂O¹²²) is shown as a red sphere. Black dotted lines represent molecular interactions less than 3.2 Å away. In the case of compounds 2 and 5, two molecules (yellow labels A and B) are bound in the PA_N ^ΔLoop active site. Gray arrows (panels B and C) show the movement of helix-α3 residue Tyr24 compared with the structure of PA_N ^ΔLoop-Apo. The atomic coordinates and structure factors for PA_N ^ΔLoop bound to compounds 1–6 have been deposited in the Protein Data Bank as PDB entries 4E5F, 4E5G, 4E5H, 4E5I, 4E5J, and 4E5L, respectively.