FIG. 1.

(a) Amino acid sequence alignment of selected IMP variants. Substitutions with IMP-1 are shown with a black background. The sequence corresponding to the mature enzyme is boldfaced (the first 18 amino acids being the signal peptide). The numbering is according to the standard scheme proposed for class B β-lactamases (8), and amino acid substitutions that are unique in IMP-18 are indicated by gray numbers. (b) Cartoon representation of the IMP-1 X-ray crystal structure (Protein Data Bank code 1DDK), showing the locations of the unique amino acid substitutions found in IMP-18. Substitutions A36D and N305S, located at the amino- and carboxy-terminal extremities of the protein, are not shown because the corresponding residues are not included in the IMP-1 structure.