5IKQ

The Structure of Meclofenamic Acid Bound to Human Cyclooxygenase-2

Summary for 5IKQ

• Entry DOI: 10.2210/pdb5ikq/pdb
• Related: 5IKR 5IKT 5IKV
• Descriptor: Prostaglandin G/H synthase 2, alpha-D-mannopyranose-(1-6)-alpha-D-mannopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose, octyl beta-D-glucopyranoside, ... (8 entities in total)
• Functional Keywords: cox meclofenamic, oxidoreductase
• Biological source: Homo sapiens (Human)
• Total number of polymer chains: 2
• Total formula weight: 131572.87

Authors

Orlando, B.J.,Malkowski, M.G. (deposition date: 2016-03-03, release date: 2016-05-25, Last modification date: 2024-10-16)

Primary citation

Orlando, B.J.,Malkowski, M.G.
Substrate-selective Inhibition of Cyclooxygeanse-2 by Fenamic Acid Derivatives Is Dependent on Peroxide Tone.
J.Biol.Chem., 291:15069-15081, 2016

PubMed Abstract: Cyclooxygenase-2 (COX-2) catalyzes the oxygenation of arachidonic acid (AA) and endocannabinoid substrates, placing the enzyme at a unique junction between the eicosanoid and endocannabinoid signaling pathways. COX-2 is a sequence homodimer, but the enzyme displays half-of-site reactivity, such that only one monomer of the dimer is active at a given time. Certain rapid reversible, competitive nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to inhibit COX-2 in a substrate-selective manner, with the binding of inhibitor to a single monomer sufficient to inhibit the oxygenation of endocannabinoids but not arachidonic acid. The underlying mechanism responsible for substrate-selective inhibition has remained elusive. We utilized structural and biophysical methods to evaluate flufenamic acid, meclofenamic acid, mefenamic acid, and tolfenamic acid for their ability to act as substrate-selective inhibitors. Crystal structures of each drug in complex with human COX-2 revealed that the inhibitor binds within the cyclooxygenase channel in an inverted orientation, with the carboxylate group interacting with Tyr-385 and Ser-530 at the top of the channel. Tryptophan fluorescence quenching, continuous-wave electron spin resonance, and UV-visible spectroscopy demonstrate that flufenamic acid, mefenamic acid, and tolfenamic acid are substrate-selective inhibitors that bind rapidly to COX-2, quench tyrosyl radicals, and reduce higher oxidation states of the heme moiety. Substrate-selective inhibition was attenuated by the addition of the lipid peroxide 15-hydroperoxyeicosatertaenoic acid. Collectively, these studies implicate peroxide tone as an important mechanistic component of substrate-selective inhibition by flufenamic acid, mefenamic acid, and tolfenamic acid.

PubMed: 27226593
DOI: 10.1074/jbc.M116.725713

Experimental method

X-RAY DIFFRACTION (2.41 Å)