Structural Basis for Imipenem Inhibition of Class C β-Lactamases

To determine how imipenem inhibits the class C β-lactamase AmpC, the X-ray crystal structure of the acyl-enzyme complex was determined to a resolution of 1.80 Å. In the complex, the lactam carbonyl oxygen of imipenem has flipped by approximately 180° compared to its expected position; the electrophilic acyl center is thus displaced from the point of hydrolytic attack. This conformation resembles that of imipenem bound to the class A enzyme TEM-1 but is different from that of moxalactam bound to AmpC.