title: Oxicams bind in a novel mode to the cyclooxygenase active site via a two-water-mediated H-bonding Network.
abstract: 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.
authors.affiliation: A. B. Hancock Jr. Memorial Laboratory for Cancer Research, Departments of Biochemistry, Chemistry, and Pharmacology, Vanderbilt Institute of Chemical Biology, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: Shu
authors.initials: S
authors.lastname: Xu
authors.affiliation: A. B. Hancock Jr. Memorial Laboratory for Cancer Research, Departments of Biochemistry, Chemistry, and Pharmacology, Vanderbilt Institute of Chemical Biology, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Hermanson
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853; Northeastern Collaborative Access Team, Argonne National Laboratory, Argonne, Illinois 60439.
authors.forename: Surajit
authors.initials: S
authors.lastname: Banerjee
authors.affiliation: A. B. Hancock Jr. Memorial Laboratory for Cancer Research, Departments of Biochemistry, Chemistry, and Pharmacology, Vanderbilt Institute of Chemical Biology, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: Kebreab
authors.initials: K
authors.lastname: Ghebreselasie
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824.
authors.forename: Gina M
authors.initials: GM
authors.lastname: Clayton
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824.
authors.forename: R Michael
authors.initials: RM
authors.lastname: Garavito
authors.affiliation: A. B. Hancock Jr. Memorial Laboratory for Cancer Research, Departments of Biochemistry, Chemistry, and Pharmacology, Vanderbilt Institute of Chemical Biology, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232. Electronic address: larry.marnett@vanderbilt.edu.
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Marnett
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000737:chemistry / Q000378:metabolism*; D001120:Arginine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D020134:Catalytic Domain; D051545:Cyclooxygenase 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016861:Cyclooxygenase Inhibitors / Q000737:chemistry / Q000378:metabolism*; D006860:Hydrogen Bonding; D007930:Leucine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000077239:Meloxicam; D051379:Mice; D009154:Mutation; D010894:Piroxicam / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D012694:Serine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013843:Thiazines / Q000737:chemistry / Q000378:metabolism*; D013844:Thiazoles / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014867:Water
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D016861:Cyclooxygenase Inhibitors; D013843:Thiazines; D013844:Thiazoles; D014867:Water; D010894:Piroxicam; D014443:Tyrosine; D012694:Serine; C013580:isoxicam; D001120:Arginine; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D007930:Leucine; D000077239:Meloxicam
keywords: Cyclooxygenase (COX) Pathway; Drug Action; Enzyme Structure; Protein Drug Interactions; X-ray Crystallography