Crystallographie study of a β-lactam inhibitor complex with elastase at 1.84 Å resolution

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Abstract
The continuing discovery and development of β-lactams as antibio-tics has had an unparalleled impact on the overall health and well-being of society. Recently, appropriately substituted cephalo-sporins were shown to be potent inhibitors of elastase1, suggesting a novel therapeutic role for the β-lactams in the control of emphysema and other degenerative diseases2,3. We have now solved and partially refined at atomic resolution the structure of a com-plex of porcine pancreatic elastase with the time-dependent irreversible inhibitor 3-acetoxymethyl-7-α-chloro-3-cephem-4-carboxylate-l,l-dioxide tert-butyl ester (I), the most potent of the β-lactam elastase inhibitors yet reported1. (Porcine pancreatic elastase is a close relative of the desired drug target, human polymorphonuclear leukocyte elastase.) A mechanism of action is presented, based on the structure and on biochemical evidence (T.-Y.L. et al., in preparation), which clarifies the operational similarities and differences between β-lactam elastase inhibitors and antibiotics. Features of the reaction include the expulsion of a leaving group at the cephalosporin 3′position and the formation of two covalent bonds with the active site of porcine pancreatic elastase at residues Ser 195 and His 57.

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