Figure 5. Hydrogen bond networks near His118 and Arg121.

Carbon is shown in tan, nitrogen is blue and oxygen is red. Water molecules are shown as red spheres and zinc is indicated as a gray sphere. Hydrogen bonds are depicted as black lines. (A) Schematic illustration of the hydrogen bond network near residue His118. Asn116, His118, Asp120, His196, Thr197 and Asp199 are group 1 residues that cannot be substituted based on deep sequencing results. Tyr117 is a group 2 residue that cannot be substituted during selections at high imipenem concentrations and Pro198 is a group 3 residue that tolerates substitutions while retaining function. (B) Schematic illustration of the hydrogen bond network near residue Arg121. Asp120, Cys221, Gly262 and His263 are group 1 residues that cannot be substituted based on deep sequencing results. Glu69, Arg121 and Asn220 are group 2 residues that cannot be substituted during selections at high imipenem concentrations. Asn70 was not mutagenized in this study.