Oxicams Bind in a Novel Mode to the Cyclooxygenase Active Site via a Two-water-mediated H-bonding Network

• Published in: The Journal of biological chemistry Vol. 289; no. 10; pp. 6799 - 6808
• Main Authors: Xu, Shu, Hermanson, Daniel J., Banerjee, Surajit, Ghebreselasie, Kebreab, Clayton, Gina M., Garavito, R. Michael, Marnett, Lawrence J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 07.03.2014; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Substitution; Animals; Anti-Inflammatory Agents, Non-Steroidal - chemistry; Anti-Inflammatory Agents, Non-Steroidal - metabolism; Arginine - chemistry; Arginine - genetics; Arginine - metabolism; Binding Sites; Catalytic Domain; Cyclooxygenase (COX) Pathway; Cyclooxygenase 1 - chemistry; Cyclooxygenase 1 - genetics; Cyclooxygenase 1 - metabolism; Cyclooxygenase 2 - chemistry; Cyclooxygenase 2 - genetics; Cyclooxygenase 2 - metabolism; Cyclooxygenase Inhibitors - chemistry; Cyclooxygenase Inhibitors - metabolism; Drug Action; Enzyme Structure; Hydrogen Bonding; Leucine - chemistry; Leucine - genetics; Leucine - metabolism; Lipids; Meloxicam; Mice; Mutation; Piroxicam - analogs & derivatives; Piroxicam - chemistry; Piroxicam - metabolism; Protein Drug Interactions; Protein Structure, Secondary; Serine - chemistry; Serine - genetics; Serine - metabolism; Thiazines - chemistry; Thiazines - metabolism; Thiazoles - chemistry; Thiazoles - metabolism; Tyrosine - chemistry; Tyrosine - genetics; Tyrosine - metabolism; Water; X-ray Crystallography; Enzyme Structure; Drug Action; X-ray Crystallography; Cyclooxygenase (COX) Pathway; Protein Drug Interactions
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.517987

Oxicams are widely used nonsteroidal anti-inflammatory drugs (NSAIDs), but little is known about the molecular basis of the interaction with their target enzymes, the cyclooxygenases (COX). Isoxicam is a nonselective inhibitor of COX-1 and COX-2 whereas meloxicam displays some selectivity for COX-2. Here we report crystal complexes of COX-2 with isoxicam and meloxicam at 2.0 and 2.45 angstroms, respectively, and a crystal complex of COX-1 with meloxicam at 2.4 angstroms. These structures reveal that the oxicams bind to the active site of COX-2 using a binding pose not seen with other NSAIDs through two highly coordinated water molecules. The 4-hydroxyl group on the thiazine ring partners with Ser-530 via hydrogen bonding, and the heteroatom of the carboxamide ring of the oxicam scaffold interacts with Tyr-385 and Ser-530 through a highly coordinated water molecule. The nitrogen atom of the thiazine and the oxygen atom of the carboxamide bind to Arg-120 and Tyr-355 via another highly ordered water molecule. The rotation of Leu-531 in the structure opens a novel binding pocket, which is not utilized for the binding of other NSAIDs. In addition, a detailed study of meloxicam·COX-2 interactions revealed that mutation of Val-434 to Ile significantly reduces inhibition by meloxicam due to subtle changes around Phe-518, giving rise to the preferential inhibition of COX-2 over COX-1. Background: The oxicams are anti-inflammatory drugs targeting the cyclooxygenase enzymes. Results: Crystal complexes of mCOX-2·isoxicam, mCOX-2·meloxicam, and oCOX-1·meloxicam are solved. Conclusion: Oxicams bind to the cyclooxygenase active sites in a novel mode. Significance: The first structural description of cyclooxygenase-oxicam complexes reveal a new binding pocket of inhibitors to cyclooxygenases.