Molecular control of δ-opioid receptor signalling

Nature (Impact Factor: 42.35). 01/2014; 506(7487). DOI: 10.1038/nature12944
Source: PubMed

ABSTRACT 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.

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    • "The insertion of b 562 RIL into ICL3 of the smoothened receptor has also been proposed as a reason for the lack of structural rearrangements at the cytoplasmic surface upon agonist binding (Wang et al., 2013b). Finally, comparison of the murine d-opioid receptor structure solved with an ICL3 T4L fusion (Granier et al., 2012) and the human d-opioid receptor with an N-terminal b 562 RIL fusion (Fenalti et al., 2014) shows a high degree of structural similarity, with the main deviations occurring proximal to the sites of fusion. "
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    ABSTRACT: G protein-coupled receptor (GPCR) structural biology has progressed dramatically in the last decade. There are now over 120 GPCR crystal structures deposited in the Protein Data Bank of 32 different receptors from families scattered across the phylogenetic tree, including Class B, C, and Frizzled GPCRs. These structures have been obtained in combination with a wide variety of ligands, and captured in a range of conformational states. This surge in structural knowledge has enlightened research into the molecular recognition of biologically active molecules, the mechanisms of receptor activation, the dynamics of functional selectivity, and fuelled structure- based drug design efforts for GPCRs. Here we summarize the innovations in both protein engineering/molecular biology and crystallography techniques that have led to these advances in GPCR structural biology, and discuss how they may influence the resulting structural models. We also provide a brief molecular pharmacologist's guide to GPCR X-ray crystallography, outlining some key aspects in the process of structure determination, with the goal to encourage non-crystallographers to interrogate structures at the molecular level. Finally we show how chemogenomics approaches can be used to marry the wealth of existing receptor pharmacology data with the expanding repertoire of structures, providing a deeper understanding of the mechanistic details of GPCR function. The American Society for Pharmacology and Experimental Therapeutics.
    Molecular pharmacology 07/2015; DOI:10.1124/mol.115.099663 · 4.12 Impact Factor
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    • "The several recent crystal structures that show interacting parallel receptors in the crystal unit cell (Fig. 3) have been used as an argument in favor of GPCR dimerization, although the possibility exists that these are crystallographic artifacts and/or they do not necessarily represent physiologically relevant interfaces. Two of the five available opioid receptor crystal structures (Fenalti et al., 2014; Granier et al., 2012; Manglik et al., 2012; Thompson et al., 2012; Wu et al., 2012), specifically the structures of μ (Manglik et al., 2012) and κ (Wu et al., 2012) receptors, also reveal parallel arrangements of interacting receptors. As shown in Fig. 3, these correspond to two different interfaces in the case of μ receptor, one of which is also seen in the κ receptor crystal "
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    ABSTRACT: Opioid receptors are important drug targets for pain management, addiction, and mood disorders. Although substantial research on these important subtypes of G protein-coupled receptors has been conducted over the past two decades to discover ligands with higher specificity and diminished side effects, currently used opioid therapeutics remain suboptimal. Luckily, recent advances in structural biology of opioid receptors provide unprecedented insights into opioid receptor pharmacology and signaling. We review here a few recent studies that have used the crystal structures of opioid receptors as a basis for revealing mechanistic details of signal transduction mediated by these receptors, and for the purpose of drug discovery. Copyright © 2015. Published by Elsevier B.V.
    European journal of pharmacology 05/2015; DOI:10.1016/j.ejphar.2015.05.012 · 2.68 Impact Factor
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    • "This sodium site appears to collapse in active-state structures, suggesting that it plays a key role in constraining GPCRs in an inactive state (Wootten et al., 2013b; Katritch et al., 2014). Interestingly, the sodium site has also been recently implicated in the regulation of biased agonism by the d-opioid receptor (Fenalti et al., 2014) and in the actions of synthetic small-molecule allosteric ligands for the m-opioid receptor (Livingston and Traynor, 2014). It should be noted, however, that a subset of class A GPCRs does not possess the requisite acidic residue at the 2.50 position. "
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    ABSTRACT: G protein-coupled receptors (GPCRs) are the largest superfamily of receptors encoded by the human genome, and also represent the largest class of current drug targets. Over the last decade and a half, it has become widely accepted that most, if not all, GPCRs possess spatially distinct allosteric sites that can be targeted by exogenous substances to modulate the receptors' biological state. Although many of these allosteric sites are likely to serve other, (e.g. structural) roles, they nonetheless possess appropriate properties to be serendipitously targeted by synthetic molecules. However, there are also examples of endogenous substances that can act as allosteric modulators of GPCRs. These not only include the obvious example, i.e., the G protein, but also a variety of ions, lipids, amino acids, peptides and accessory proteins that display different degrees of receptor-specific modulatory effects. This also suggests that some GPCRs may possess true 'orphan' allosteric sites for hitherto unappreciated endogenous modulators. Of note, the increasing identification of allosteric modulator lipids, inflammatory peptides and GPCR-targeted autoantibodies indicates that disease context plays an important role in the generation of putative endogenous GPCR modulators. If an endogenous allosteric substance can be shown to play a role in disease, this could also serve as an impetus to pursue synthetic neutral allosteric ligands (NALs) as novel therapeutic agents. The American Society for Pharmacology and Experimental Therapeutics.
    Journal of Pharmacology and Experimental Therapeutics 02/2015; 353(2). DOI:10.1124/jpet.114.221606 · 3.86 Impact Factor
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