3D model of IMP-1 metallo-β-lactamase, generated with PyMOL (www.pymol.com) by using the crystal structure 1DD6 (23). The enzyme backbone is represented as a gray ribbon, and atoms of key active site residues are shown as sticks colored in green (carbon), red (oxygen), blue (nitrogen), yellow (sulfur), and white (hydrogen). The Zn(II) ions are represented by dark gray spheres. The residue under investigation at position 67 is indicated by a red box.