Journal Article

Molecular control of δ-opioid receptor signalling

Huang, Xi-Ping, Cherezov, Vadim, Fenalti, Gustavo, Giguere, Patrick M., Stevens, Raymond C., Roth, Bryan L., Thompson, Aaron A., Katritch, Vsevolod

2014

Overview

Opioids represent widely prescribed and abused medications, although their signal transduction mechanisms are not well understood. Here we present the 1.8 Å high-resolution crystal structure of the human δ-opioid receptor (δ-OR), revealing the presence and fundamental role of a sodium ion in mediating allosteric control of receptor functional selectivity and constitutive activity. The distinctive δ-OR sodium ion site architecture is centrally located in a polar interaction network in the seven-transmembrane bundle core, with the sodium ion stabilizing a reduced agonist affinity state, and thereby modulating signal transduction. Site-directed mutagenesis and functional studies reveal that changing the allosteric sodium site residue Asn 131 to an alanine or a valine augments constitutive β-arrestin-mediated signalling. Asp95Ala, Asn310Ala and Asn314Ala mutations transform classical δ-opioid antagonists such as naltrindole into potent β-arrestin-biased agonists. The data establish the molecular basis for allosteric sodium ion control in opioid signalling, revealing that sodium-coordinating residues act as ‘efficacy switches’ at a prototypic G-protein-coupled receptor. The 1.8 Å high-resolution X-ray crystal structure of the human δ-opioid receptor is presented, with site-directed mutagenesis and functional studies revealing a crucial role for a sodium ion in mediating allosteric control in this receptor. Making dual-action opioids Opioid receptors mediate the actions of endogenous and exogenous opioids for many physiological processes, including analgesia, consciousness, motor control and mood. This paper reports the X-ray crystal structure of the human δ-opioid receptor at 1.8 Å resolution, revealing the presence of a sodium ion that seems to mediate allosteric control of this G-protein-coupled receptor. Site-directed mutagenesis and functional studies show that mutating key amino acids in the allosteric sodium site to alanine transforms the antagonist naltrindole into a potent β-arrestin-biased agonist. Also apparent is an allosteric sodium-binding pocket that could aid the development of subtype-selective δ-opioid receptor agonists and antagonists — the extension of orthosteric ligands into the pocket could generate 'bitopic' orthosteric/allosteric compounds with more favourable pharmacological properties.

• Publisher: Nature Publishing Group UK
• Subject: 631/45/535/1266 / 631/92 / 82/47 / 82/80 / 82/83 / Allosteric Regulation - drug effects / Allosteric Regulation - genetics / Allosteric Site - drug effects / Allosteric Site - genetics / Arrestins - metabolism / Asparagine - genetics / Asparagine - metabolism / beta-Arrestins / Crystallography, X-Ray / Humanities and Social Sciences / Humans / Ligands / Models, Molecular / multidisciplinary / Mutagenesis, Site-Directed / Naltrexone - analogs & derivatives / Naltrexone - chemistry / Naltrexone - metabolism / Naltrexone - pharmacology / Narcotic Antagonists - chemistry / Narcotic Antagonists - metabolism / Narcotic Antagonists - pharmacology / Receptors, Opioid, delta - agonists / Receptors, Opioid, delta - antagonists & inhibitors / Receptors, Opioid, delta - chemistry / Receptors, Opioid, delta - genetics / Receptors, Opioid, delta - metabolism / Science / Signal Transduction - drug effects / Sodium - metabolism / Sodium - pharmacology / Structure-Activity Relationship