Article

Structure of the Nociceptin/Orphanin FQ Receptor in Complex with a Peptide Mimetic

Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Nature (Impact Factor: 42.35). 05/2012; 485(7398):395-9. DOI: 10.1038/nature11085
Source: PubMed

ABSTRACT Members of the opioid receptor family of G-protein-coupled receptors (GPCRs) are found throughout the peripheral and central nervous system, where they have key roles in nociception and analgesia. Unlike the 'classical' opioid receptors, δ, κ and μ (δ-OR, κ-OR and μ-OR), which were delineated by pharmacological criteria in the 1970s and 1980s, the nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP, also known as ORL-1) was discovered relatively recently by molecular cloning and characterization of an orphan GPCR. Although it shares high sequence similarity with classical opioid GPCR subtypes (∼60%), NOP has a markedly distinct pharmacology, featuring activation by the endogenous peptide N/OFQ, and unique selectivity for exogenous ligands. Here we report the crystal structure of human NOP, solved in complex with the peptide mimetic antagonist compound-24 (C-24) (ref. 4), revealing atomic details of ligand-receptor recognition and selectivity. Compound-24 mimics the first four amino-terminal residues of the NOP-selective peptide antagonist UFP-101, a close derivative of N/OFQ, and provides important clues to the binding of these peptides. The X-ray structure also shows substantial conformational differences in the pocket regions between NOP and the classical opioid receptors κ (ref. 5) and μ (ref. 6), and these are probably due to a small number of residues that vary between these receptors. The NOP-compound-24 structure explains the divergent selectivity profile of NOP and provides a new structural template for the design of NOP ligands.

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Available from: Claudio Trapella, Aug 19, 2015
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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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    European journal of pharmacology 05/2015; DOI:10.1016/j.ejphar.2015.05.012 · 2.68 Impact Factor
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    • "), the native N-terminal tetrapeptide (FGGF) was identified as the message domain, essential for activating biological responses following receptor binding, while the remainder of its sequence, termed the address domain, likely confers high-affinity binding (Fig. 4). The address domain of nociceptin (i.e., residues 7–17) contains basic amino acid residues that likely bind to acidic residues present in the second extracellular loop of the ORL-1 receptor (Thompson et al., 2012). Nociceptin (nociceptin(1–17)-OH) is equipotent with its amidated form (nociceptin(1–17)-NH 2 ; Guerrini et al., 1997), yet truncation of the nociceptin sequence possessing either a free acid or an amidated C-terminus resulted in substantial changes in binding affinity for ORL-1 (Butour et al., 1997; Calo et al., 1997; Dooley & Houghten, 1996; Guerrini et al., 1997). "
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    ABSTRACT: Nociceptin (orphanin FQ) is a 17-residue neuropeptide hormone with roles in both nociception and analgesia. It is an opioid-like peptide that binds to and activates the G-protein-coupled receptor opioid receptor-like-1 (ORL-1, NOP, orphanin FQ receptor, kappa-type 3 opioid receptor) on central and peripheral nervous tissue, without activating classic delta-, kappa-, or mu-opioid receptors or being inhibited by the classic opioid antagonist naloxone. The three-dimensional structure of ORL-1 was recently published, and the activation mechanism is believed to involve capture by ORL-1 of the high-affinity binding, prohelical C-terminus. This likely anchors the receptor- activating N-terminus of nociception nearby for insertion in the membrane-spanning helices of ORL-1. In search of higher agonist potency, two lysine and two aspartate res- idues were strategically incorporated into the receptor-binding C-terminus of the nociceptin sequence and two Lys(i)!Asp(i+4) side chain–side chain condensations were used to generate lactam cross-links that constrained nociceptin into a highly stable α-helix in water. A cell-based assay was developed using natively expressed ORL-1 receptors on mouse neuroblastoma cells to measure phosphorylated ERK as a reporter of agonist-induced receptor activation and intracellular signaling. Agonist activity was increased up to 20-fold over native nociceptin using a combination of this helix-inducing strategy and other amino acid modifications. An NMR-derived three-dimensional solution structure is described for a potent ORL-1 agonist derived from nociceptin, along with structure–activity relationships leading to the most potent known α-helical ORL-1 agonist (EC50 40 pM, pERK, Neuro-2a cells) and antagonist (IC50 7 nM, pERK, Neuro-2a cells). These α-helix-constrained mimetics of nociceptin(1–17) had enhanced serum stability relative to unconstrained peptide analogues and nociceptin itself, were not cytotoxic, and displayed potent thermal analgesic and antianalgesic properties in rats (ED50 70 pmol, IC50 10 nmol, s.c.), suggesting promising uses in vivo for the treatment of pain and other ORL-1-mediated responses.
    Nociceptin Opioid, 97 edited by Gerald Litwak, 01/2015: chapter 1: pages 1-55; Elsevier.
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    • "In fact, the crystal structure of the human NOP receptor, solved in complex with the peptide mimetic antagonist compound-24 (C-24) revealed substantial conformational differences in the binding pocket regions between the NOP receptor and opioid receptors (Thompson et al., 2012). The crystal structure of the NOP receptor provides evidence that the three residues Ala 216 , Gln 280 and Thr 305 point towards the interior of the binding pocket and that Gln 280 and Thr 305 are involved in C-24 interaction. "
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    ABSTRACT: Despite high sequence similarity between NOP (nociceptin/orphaninFQ opioid peptide) and opioid receptors, marked differences in endogenous ligand selectivity, signal transduction, phosphorylation, desensitization, internalization and trafficking have been identified; underscoring the evolutionary difference between NOP and opioid receptors. Activation of NOP receptors affects nociceptive transmission in a site-specific manner, with antinociceptive effects prevailing after peripheral and spinal activation, and pronociceptive effects after supraspinal activation in rodents. The net effect of systemically administered NOP receptor agonists on nociception is proposed to depend on the relative contribution of peripheral, spinal and supraspinal activation and this may depend on experimental conditions. Functional expression and regulation of NOP receptors at peripheral and central sites of the nociceptive pathway exhibits a high degree of plasticity under conditions of neuropathic and inflammatory pain. In rodents, systemically administered NOP receptor agonists exerted antihypersensitive effects in models of neuropathic and inflammatory pain. However they were largely ineffective in acute pain while concomitantly evoking severe motor side effects. In contrast, systemic administration of NOP receptor agonists to non-human primates (NHPs) exerted potent and efficacious antinociception in the absence of motor and sedative side effects. The reason for this species difference with respect to antinociceptive efficacy and tolerability is not clear. Moreover, co-activation of NOP and μ-opioid peptide (MOP) receptors synergistically produced antinociception in NHPs. Hence, both selective NOP receptor as well as NOP/MOP receptor agonists may hold potential for clinical use as analgesics effective in conditions of acute and chronic pain.
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