Structural basis for imipenem inhibition of class C beta-lactamases.

To determine how imipenem inhibits the class C beta-lactamase AmpC, the X-ray crystal structure of the acyl-enzyme complex was determined to a resolution of 1.80 A. In the complex, the lactam carbonyl oxygen of imipenem has flipped by approximately 180 degrees 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.