FIG. 4.

Stereo view of the β4-α4 and α4 areas of PhoPN. The protein backbone is indicated by black lines; oxygen atoms are red, carbon atoms are grey, nitrogen atoms are blue, and sulfur atoms are yellow. Residue F87 from the β4-α4 loop contributes to the hydrophobic pocket and anchors this region to the protein core. The hydrogen bond (green dashed lines) between D53 and the main chain carbonyl atom of E85 involves three water molecules (small red spheres) and may stabilize the conformation of the loop.