Inhibition of elastase by N-sulfonylaryl beta-lactams: Anatomy of a stableacyl-enzyme complex

beta-Lactam inhibitors of transpeptidase enzymes involved in cell wall bios ynthesis remain among the most important therapeutic agents in clinical use . beta-Lactams have more recently been developed as inhibitors of serine pr oteases including elastase. All therapeutically useful beta-lactam inhibito rs operate via mechanisms resulting in the formation of hydrolytically stab le acyl-enzyme complexes. Presently, it is difficult to predict which beta- lactams will form stable acyl-enzyme complexes with serine enzymes. Further , the factors that result in the seemingly special nature of beta-lactams v ersus other acylating agents are unclear-if indeed they exist. Here we pres ent the 1.6 Angstrom resolution crystal structure of a stable acyl-enzyme c omplex formed between porcine pancreatic elastase and a representative mono cyclic beta-lactam, which forms a simple acyl-enzyme. The structure shows t hat the ester carbonyl is not located within the oxyanion hole and the "hyd rolytic" water is displaced. Combined with additional kinetic and mass spec trometric data, the structure allows the rationalization of the low degree of hydrolytic lability observed for the beta-lactam-derived acyl-enzyme com plex.