 |
PDBsum entry 5ikq
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Oxidoreductase
|
PDB id
|
|
|
|
5ikq
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Substrate-Selective inhibition of cyclooxygeanse-2 by fenamic acid derivatives is dependent on peroxide tone.
|
|
|
Authors
|
|
B.J.Orlando,
M.G.Malkowski.
|
|
|
Ref.
|
|
J Biol Chem, 2016,
291,
15069-15081.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
