Fig. 3.

Spacefill diagram of the IMP-1 metallo-β-lactamase structure showing the mutagenized residues of the 27 random libraries. The residues are divided into three groups: critical, represents positions that do not allow any substitutions (red); restrictive, represents positions that allow 1–2 substitutions (yellow); and tolerant, represents positions that allow 3–6 substitutions (blue). The two green spheres represent zinc molecules. The figure was rendered using the Molscript and Raster3d programs (Kraulis 1991; Merritt and Murphy 1994) using coordinates from the Protein Data Bank accession code 1DD6 (Concha et al. 2000).