The role of water molecules in the deacylation of acylated structures of class A beta-lactamase.

Molecular dynamics simulation of the penicillin- and penem-acylated enzymes reveals that the conformational flexibility of the acyl moieties in the binding cleft and the conformational change of the acyl moieties are crucial for deacylation. The water molecule adjacent to the Glu 166 residue is not the nucleophile for deacylation, but construction of a model of the oxyanion tetrahedral intermediate suggested a plausible role of the water molecule as a proton donor for the oxyanion to facilitate the deacylation.