FIGURE 2.

A, structure of KPC-2 (Protein Data Bank code 2OV1). The nucleophile Ser-70 and residue of focus in this study, Arg-164, are indicated. Active site regions are color-coded as follows: orange, SXXK motif (residues 70–73); green, SDN loop (130–132); blue, Ω-loop (164–179); red, b3 β-strand (234–242). B, sequence alignment of the Ω-loops of KPC-2 with other class A carbapenemases (blue), penicillinases (red), and cephalosporinases (green). Note the strict conservation of Arg-164 and Asp-179. C, overlay of Ω-loops from TEM-1 (red) and KPC-2 (blue), showing the salt bridge between Arg-164 and Asp-179.