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Modulation of ?-opioid receptor activation by acidic pH is dependent on ligand structure and an ionizable amino acid residue.

ABSTRACT: BACKGROUND AND PURPOSE:Adverse side effects of conventional opioids can be avoided if ligands selectively activate peripheral opioid receptors in injured tissue. Injury and inflammation are typically accompanied by acidification. In this study, we examined influences of low pH and mutation of the ionizable amino acid residue H2976.52 on ?-opioid receptor binding and signalling induced by the ?-opioid receptor ligands fentanyl, DAMGO, and naloxone. EXPERIMENTAL APPROACH:HEK 293 cells stably transfected with ?-opioid receptors were used to study opioid ligand binding, [35 S]-GTP?S binding, and cAMP reduction at physiological and acidic pH. We used ?-opioid receptors mutated at H2976.52 to A (MOR-H2976.52 A) to delineate ligand-specific interactions with H2976.52 . KEY RESULTS:Low pH and the mutant receptor MOR-H2976.52 A impaired naloxone binding and antagonism of cAMP reduction. In addition, DAMGO binding and G-protein activation were decreased under these conditions. Fentanyl-induced signalling was not influenced by pH and largely independent of H2976.52 . CONCLUSIONS AND IMPLICATIONS:Our investigations indicate that low pH selectively impairs ?-opioid receptor signalling modulated by ligands capable of forming hydrogen bonds with H2976.52 . We propose that protonation of H2976.52 at acidic pH reduces binding and subsequent signalling of such ligands. Novel agonists targeting opioid receptors in injured tissue might benefit from lack of hydrogen bond formation with H2976.52 .

SUBMITTER: Meyer J

PROVIDER: S-EPMC6932940 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Modulation of μ-opioid receptor activation by acidic pH is dependent on ligand structure and an ionizable amino acid residue.

Meyer Johanna J Del Vecchio Giovanna G Seitz Viola V Massaly Nicolas N Stein Christoph C

British journal of pharmacology 20191205 23

<h4>Background and purpose</h4>Adverse side effects of conventional opioids can be avoided if ligands selectively activate peripheral opioid receptors in injured tissue. Injury and inflammation are typically accompanied by acidification. In this study, we examined influences of low pH and mutation of the ionizable amino acid residue H297<sup>6.52</sup> on μ-opioid receptor binding and signalling induced by the μ-opioid receptor ligands fentanyl, DAMGO, and naloxone.<h4>Experimental approach</h4> ...[more]

PMID: 31355457

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Project description:The role of pH in regulating biological activity is ubiquitous, and understanding pH-mediated activity has traditionally relied on analyzing static biomolecular structures of highly populated ground states solved near physiological pH. However, recent advances have shown the increasing importance of transiently populated states, the characterization of which is extremely challenging but made plausible with the development of techniques such as relaxation dispersion NMR spectroscopy. To unlock the pH dependence of these transient states with atomistic-level details, we applied the recently developed explicit solvent constant pH molecular dynamics (CPHMD(MSλD)) framework to a series of staphylococcal nuclease (SNase) mutants with buried ionizable residues and probed their dynamics in different pH environments. Among our key findings is the existence of open states in all SNase mutants containing "buried" residues with highly shifted pKa's, where local solvation around the protonation site was observed. The calculated pKa demonstrated good agreement with experimental pKa's, with a low average unsigned error of 1.3 pKa units and correlation coefficient R(2) = 0.78. Sampling both open and closed states in their respective pH range, where they are expected to be dominant, was necessary to reproduce experimental pKa's, and in the most extreme examples of pKa shifts measured, it can be interpreted that the open-state structures are transient at physiological pH, contributing a small population of 1-2%. This suggests that buried ionizable residues can trigger conformational fluctuations that may be observed as transient-state structures at physiological pH. Furthermore, the coupled relationship of both open and closed states and their role in recapitulating macroscopic experimental observables suggest that structural analysis of buried residues may benefit from looking at structural pairs, as opposed to the conventional approach of looking at a single static ground-state conformation.

Dataset Information

Modulation of ?-opioid receptor activation by acidic pH is dependent on ligand structure and an ionizable amino acid residue.

Publications

Modulation of μ-opioid receptor activation by acidic pH is dependent on ligand structure and an ionizable amino acid residue.

Similar Datasets

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