101
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Zhang YQ, Limbird LE. Hetero-oligomers of alpha2A-adrenergic and mu-opioid receptors do not lead to transactivation of G-proteins or altered endocytosis profiles. Biochem Soc Trans 2005; 32:856-60. [PMID: 15494033 DOI: 10.1042/bst0320856] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Complexes of alpha(2A)-ARs (alpha(2A)-adrenergic receptors) and MORs (mu-opioid receptors), probably hetero-oligomers, were detected by co-immunoisolation after extraction from HEK-293 cells (human embryonic kidney 293 cells). Functional communication between these receptors is revealed by alpha(2A)-AR activation of a pertussis toxin-insensitive G(i)alpha subunit (termed as G(i)1) when fused with the MOR and evaluated in membranes from pertussis toxin-treated cells. However, the alpha(2A)-AR does not require transactivation through MOR, since quantitatively indistinguishable results were observed in cells co-expressing alpha(2A)-AR and a fusion protein of G(i)1 with the first transmembrane span of MOR (myc-MOR-TM1). Functional cross-talk among these alpha(2A)-AR-MOR complexes does not occur for internalization profiles; incubation with adrenaline (epinephrine) leads to endocytosis of alpha(2A)-AR but not MOR, while incubation with DAMGO ([D-Ala,NMe-Phe,Gly-ol]enkephalin) leads to endocytosis of MOR but not alpha(2A)-AR in cells co-expressing both the receptors. Hence, alpha(2A)-AR and MOR hetero-oligomers, although they occur, do not have an obligatory functional influence on one another in the paradigms studied.
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102
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Grieco P, Giusti L, Carotenuto A, Campiglia P, Calderone V, Lama T, Gomez-Monterrey I, Tartaro G, Mazzoni MR, Novellino E. Morphiceptin Analogues Containing a Dipeptide Mimetic Structure: An Investigation on the Bioactive Topology at the μ-Receptor. J Med Chem 2005; 48:3153-63. [PMID: 15857121 DOI: 10.1021/jm040867y] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We describe the design, the conformational behavior, and the biological activity at the mu-opioid receptor of new morphiceptin analogues. In these analogues a recently described dipeptide mimetic structure replaces both the N- and the C-terminal Xaa-Pro dipeptide of morphiceptin. Conformational investigation on the most active analogue, compared to the parent peptide, indicates a high degree of structural tolerance within the mu-opioid receptor binding site. In fact, our results indicate that only the location and the relative orientation of the side chains of the aromatic pharmacophoric residues represent the indispensable structural features for mu-receptor binding. To reach such topological arrangement, opioid peptides can adopt different conformations and configurations. In particular, opioid peptides bearing a proline residue as spacer between the two aromatic residues can adopt, in the active state, both cis and trans configurations at the Tyr(1)-Pro(2) amide bond, each of them with the appropriate backbone and side chains orientations.
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103
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Ott D, Neldner Y, Cèbe R, Dodevski I, Plückthun A. Engineering and functional immobilization of opioid receptors. Protein Eng Des Sel 2005; 18:153-60. [PMID: 15790572 DOI: 10.1093/protein/gzi012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Opioid receptors, like many G protein-coupled receptors (GPCRs), are notoriously unstable in detergents. We have now developed a more stable variant of the mu-opioid receptor (MOR) and also a method for the immobilization of solubilized, functional opioid receptors on a solid phase (magnetic beads). Starting with the intrinsically more stable kappa-opioid receptor (KOR), we optimized the conditions (i.e. detergents and stabilizing ligands) for receptor extraction from lipid bilayers of HEK293T cells to obtain maximal amounts of functional, immobilized receptor. After immobilization, the ligand binding profile remains the same as observed for the membrane-embedded receptor. For the immobilized wild-type mu-opioid receptor, however, no conditions were found under which ligand binding capacity was retained. To solve this problem, we engineered the receptor chimera KKM where the N-terminus and the first transmembrane helix (TM1) of wild-type MOR is exchanged for the homologous receptor parts of the wild-type KOR. This hybrid receptor behaves exactly as the wild-type MOR in functional assays. Interestingly, the modified MOR is expressed at six times higher levels than wild-type MOR and is similarly stable as wild-type KOR after immobilization. Hence the immobilized MOR, represented by the chimera KKM, is now also amenable for biophysical characterization. These results are encouraging for future stability engineering of GPCRs.
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104
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Zhang Y, Sham YY, Rajamani R, Gao J, Portoghese PS. Homology Modeling and Molecular Dynamics Simulations of the Mu Opioid Receptor in a Membrane-Aqueous System. Chembiochem 2005; 6:853-9. [PMID: 15776407 DOI: 10.1002/cbic.200400207] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Three types of opioid receptors-mu, delta, and kappa-belong to the rhodopsin subfamily in the G protein-coupled receptor superfamily. With the recent characterization of the high-resolution X-ray crystal structure of bovine rhodopsin, considerable attention has been focused on molecular modeling of these transmembrane proteins. In this study, a homology model of the mu opioid receptor was constructed based on the X-ray crystal structure of bovine rhodopsin. A phospholipid bilayer was built around the receptor, and two water layers were placed on both surfaces of the lipid bilayer. Molecular-dynamics simulations were carried out by using CHARMM for the entire system, which consisted of 316 amino acid residues, 92 phospholipid molecules, 8327 water molecules, and 11 chloride counter ions-40 931 atoms altogether. The whole system was equilibrated for 250 ps followed by another 2 ns dynamic simulation. The opioid ligand naltrexone was docked into the optimized model, and the critical amino acid residues for binding were identified. The mu opioid receptor homology model optimized in a complete membrane-aqueous system should provide a good starting point for further characterization of the binding modes for opioid ligands. Furthermore, the method developed herein will be applicable to molecular model building to other opioid receptors as well as other GPCRs.
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MESH Headings
- Animals
- Binding Sites
- Cattle
- Cell Membrane/chemistry
- Cell Membrane/metabolism
- Computer Simulation
- Crystallography, X-Ray
- Lipid Metabolism
- Lipids/chemistry
- Models, Molecular
- Naltrexone/analogs & derivatives
- Naltrexone/chemistry
- Naltrexone/pharmacology
- Protein Structure, Tertiary
- Receptors, Opioid, mu/antagonists & inhibitors
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/metabolism
- Rhodopsin/chemistry
- Sequence Homology
- Solvents/chemistry
- Solvents/metabolism
- Structural Homology, Protein
- Water/chemistry
- Water/metabolism
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105
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Law PY, Erickson-Herbrandson LJ, Zha QQ, Solberg J, Chu J, Sarre A, Loh HH. Heterodimerization of μ- and δ-Opioid Receptors Occurs at the Cell Surface Only and Requires Receptor-G Protein Interactions. J Biol Chem 2005; 280:11152-64. [PMID: 15657030 DOI: 10.1074/jbc.m500171200] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Homo- and heterodimerization of the opioid receptors with functional consequences were reported previously. However, the exact nature of these putative dimers has not been identified. In current studies, the nature of the heterodimers was investigated by producing the phenotypes of the 1:1 heterodimers formed between the constitutively expressed mu-opioid receptor (MOR) and the ponasterone A-induced expression of delta-opioid receptor (DOR) in EcR293 cells. By examining the trafficking of the cell surface-located MOR and DOR, we determined that these two receptors endocytosed independently. Using cell surface expression-deficient mutants of MOR and DOR, we observed that the corresponding wild types of these receptors could not rescue the cell surface expression of the mutants, whereas the antagonist naloxone could. Furthermore, studies with constitutive or agonist-induced receptor internalization also indicated that MOR and DOR endocytosed independently and could not "drag in" the corresponding wild types or endocytosis-deficient mutants. Additionally, the heterodimer phenotypes could be eliminated by the pretreatment of the EcR293 cells with pertussis toxin and could be modulated by the deletion of the RRITR sequence in the third intracellular loop that is involved in the receptor-G protein interaction and activation. These data suggest that MOR and DOR heterodimerize only at the cell surface and that the oligomers of opioid receptors and heterotrimeric G protein are the bases for the observed MOR-DOR heterodimer phenotypes.
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MESH Headings
- Animals
- Cell Line
- Dimerization
- Endocytosis
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacology
- Enkephalin, D-Penicillamine (2,5)-/pharmacology
- Heterotrimeric GTP-Binding Proteins/physiology
- Humans
- Mice
- Pertussis Toxin/pharmacology
- Receptors, Opioid, delta/chemistry
- Receptors, Opioid, delta/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/metabolism
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106
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Garzón J, Rodríguez-Muñoz M, López-Fando A, Sánchez-Blázquez P. Activation of μ-Opioid Receptors Transfers Control of Gα Subunits to the Regulator of G-protein Signaling RGS9-2. J Biol Chem 2005; 280:8951-60. [PMID: 15632124 DOI: 10.1074/jbc.m407005200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
In mouse periaqueductal gray matter (PAG) membranes, the mu-opioid receptor (MOR) coprecipitated the alpha-subunits of the Gi/o/z/q/11 proteins, the Gbeta1/2 subunits, and the regulator of G-protein signaling RGS9-2 and its partner protein Gbeta5. RGS7 and RGS11 present in this neural structure showed no association with MOR. In vivo intracerebroventricular injection of morphine did not alter MOR immunoreactivity, but 30 min and 3 h after administration, the coprecipitation of Galpha subunits with MORs was reduced by up to 50%. Furthermore, the association between Galpha subunits and RGS9-2 proteins was increased. Twenty-four hours after receiving intracerebroventricular morphine, the Galpha subunits left the RGS9-2 proteins and re-associated with the MORs. However, doses of the opioid able to induce tolerance promoted the stable transfer of Galpha subunits to the RGS9-2 control. This was accompanied by Ser phosphorylation of RGS9-2 proteins, which increased their co-precipitation with 14-3-3 proteins. In the PAG membranes of morphine-desensitized mice, the capacity of the opioid to stimulate G-protein-related guanosine 5'-O-(3-[35S]thiotriphosphate) binding as well as low Km GTPase activity was attenuated. The in vivo knockdown of RGS9-2 expression prevented morphine from altering the association between MORs and G-proteins, and tolerance did not develop. In PAG membranes from RGS9-2 knockdown mice, morphine showed full capacity to activate G-proteins. Thus, the tolerance that develops following an adequate dose of morphine is caused by the stabilization and retention of MOR-activated Galpha subunits by RGS9-2 proteins. This multistep process is initiated by the morphine-induced transfer of MOR-associated Galpha subunits to the RGS9-2 proteins, followed by Ser phosphorylation of the latter and their binding to 14-3-3 proteins. This regulatory mechanism probably precedes the loss of MORs from the cell membrane, which has been observed with other opioid agonists.
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107
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Peng Y, Keenan SM, Zhang Q, Kholodovych V, Welsh WJ. 3D-QSAR Comparative Molecular Field Analysis on Opioid Receptor Antagonists: Pooling Data from Different Studies. J Med Chem 2005; 48:1620-9. [PMID: 15743203 DOI: 10.1021/jm049117e] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Three-dimensional quantitative structure-activity relationship (3D-QSAR) models were constructed using comparative molecular field analysis (CoMFA) on a series of opioid receptor antagonists. To obtain statistically significant and robust CoMFA models, a sizable data set of naltrindole and naltrexone analogues was assembled by pooling biological and structural data from independent studies. A process of "leave one data set out", similar to the traditional "leave one out" cross-validation procedure employed in partial least squares (PLS) analysis, was utilized to study the feasibility of pooling data in the present case. These studies indicate that our approach yields statistically significant and highly predictive CoMFA models from the pooled data set of delta, mu, and kappa opioid receptor antagonists. All models showed excellent internal predictability and self-consistency: q(2) = 0.69/r(2) = 0.91 (delta), q(2) = 0.67/r(2) = 0.92 (mu), and q(2) = 0.60/r(2) = 0.96 (kappa). The CoMFA models were further validated using two separate test sets: one test set was selected randomly from the pooled data set, while the other test set was retrieved from other published sources. The overall excellent agreement between CoMFA-predicted and experimental binding affinities for a structurally diverse array of ligands across all three opioid receptor subtypes gives testimony to the superb predictive power of these models. CoMFA field analysis demonstrated that the variations in binding affinity of opioid antagonists are dominated by steric rather than electrostatic interactions with the three opioid receptor binding sites. The CoMFA steric-electrostatic contour maps corresponding to the delta, mu, and kappa opioid receptor subtypes reflected the characteristic similarities and differences in the familiar "message-address" concept of opioid receptor ligands. Structural modifications to increase selectivity for the delta over mu and kappa opioid receptors have been predicted on the basis of the CoMFA contour maps. The structure-activity relationships (SARs) together with the CoMFA models should find utility for the rational design of subtype-selective opioid receptor antagonists.
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MESH Headings
- Least-Squares Analysis
- Ligands
- Models, Molecular
- Naltrexone/analogs & derivatives
- Naltrexone/chemistry
- Narcotic Antagonists
- Quantitative Structure-Activity Relationship
- Receptors, Opioid/chemistry
- Receptors, Opioid, delta/antagonists & inhibitors
- Receptors, Opioid, delta/chemistry
- Receptors, Opioid, kappa/antagonists & inhibitors
- Receptors, Opioid, kappa/chemistry
- Receptors, Opioid, mu/antagonists & inhibitors
- Receptors, Opioid, mu/chemistry
- Static Electricity
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108
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Fowler CB, Pogozheva ID, Lomize AL, LeVine H, Mosberg HI. Complex of an active mu-opioid receptor with a cyclic peptide agonist modeled from experimental constraints. Biochemistry 2005; 43:15796-810. [PMID: 15595835 DOI: 10.1021/bi048413q] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Site-directed mutagenesis and design of Zn(2+)-binding centers have been used to determine a set of specific tertiary interactions between the mu-opioid receptor, a rhodopsin-like G protein-coupled receptor (GPCR), and its cyclic peptide agonist ligand, Tyr(1)-c(S-Et-S)[d-Cys(2)-Phe(3)-d-Pen(4)]NH(2) (JOM6). The binding affinity of the tetrapeptide is strongly dependent on the nature of its first and third residues and on substitutions at positions 213, 216, 237, 300, 315, and 318 of the mu-opioid receptor. His(1) and His(3) analogues of the ligand were able to form metal-binding complexes with the V300C and G213C/T315C receptor mutants, respectively. Direct contact of the Phe(3) residue of JOM6 with Gly(213), Asp(216), Thr(315), and Trp(318) of the receptor was suggested by the binding affinities of His(3)-, Nle(3)-, Leu(3)-, Aci(3)-, Delta(E)Phe(3)-, and Delta(Z)Phe(3)-substituted peptides with the G213C/T315C, D216V, T315C, and W318L mutants. The improved binding affinity of the free carboxylate analogue of JOM6 for binding to the E229D mutant revealed an interaction between the C-terminal group of the peptide and Glu(229) of the receptor. The experimental constraints that were obtained were applied for distance geometry modeling of the mu-receptor in complex with the tetrapeptide agonist ligand, JOM6. The active conformation of the opioid receptor was calculated using the crystal structure of "inactive" rhodopsin and published engineered and intrinsic metal-binding sites and disulfide bonds that allow or facilitate activation of GPCRs. Interhelical H-bonds existing in the mu-receptor were applied as additional distance constraints. The calculated model of the receptor-ligand complex can serve as a prototype of the active state for all rhodopsin-like GPCRs. It displays a strongly shifted transmembrane helix 6 (TM6) and reorientation of the conserved Trp(293) residue in TM6 upon its interaction with the agonist. Importantly, the binding pockets of the active and inactive states are not identical, which implies distinct interaction modes of agonists and antagonists. In the active state, the binding pocket of the mu-receptor is complementary to the previously proposed receptor-bound conformation of JOM6.
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MESH Headings
- Amino Acid Sequence
- Amino Acid Substitution/genetics
- Animals
- Binding Sites/genetics
- COS Cells
- Cattle
- Chlorocebus aethiops
- DNA Mutational Analysis
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Peptides, Cyclic/chemistry
- Peptides, Cyclic/genetics
- Peptides, Cyclic/pharmacology
- Point Mutation/genetics
- Protein Conformation
- Rats
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/genetics
- Zinc/metabolism
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109
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Kerman A, Ananthanarayanan VS. Expression and spectroscopic characterization of a large fragment of the μ-opioid receptor. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2005; 1747:133-40. [PMID: 15680247 DOI: 10.1016/j.bbapap.2004.10.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2004] [Revised: 10/13/2004] [Accepted: 10/13/2004] [Indexed: 11/28/2022]
Abstract
We report here a procedure for the production in Escherichia coli and subsequent purification and characterization of an 80-residue fragment of the human mu-opioid receptor. The fragment ('TM2-3'), which comprises the second and third transmembrane segments as well as the first extracellular loop of the receptor, was expressed as a fusion with glutathione-S-transferase. The fusion protein, which accumulated in insoluble inclusion bodies, was solubilized with N-lauroylsarcosine, and TM2-3 was obtained by thrombin cleavage of the fusion protein followed by reversed-phase HPLC purification. CD spectroscopy of TM2-3 in lysophosphatidylcholine micelles showed that TM2-3 adopts approximately 50% alpha-helical structure in this environment, with the remainder consisting of disordered and/or beta-structure. This is consistent with the assumption of an alpha-helical structure by the two membrane-spanning regions and a nonhelical structure in the loop region of TM2-3. Fluorescence spectroscopy and fluorescence quenching experiments suggested that the extracellular loop lies near the surface of the lysophosphatidylcholine micelle. Our work shows that the study of large receptor fragments is a technically accessible approach to the study of the structural properties of the mu-opioid receptor and, possibly, other G-protein-coupled receptors as well.
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110
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Liao D, Lin H, Law PY, Loh HH. Mu-opioid receptors modulate the stability of dendritic spines. Proc Natl Acad Sci U S A 2005; 102:1725-30. [PMID: 15659552 PMCID: PMC545084 DOI: 10.1073/pnas.0406797102] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Opioids classically regulate the excitability of neurons by suppressing synaptic GABA release from inhibitory neurons. Here, we report a role for opioids in modulating excitatory synaptic transmission. By activating ubiquitously clustered mu-opioid receptor (MOR) in excitatory synapses, morphine caused collapse of preexisting dendritic spines and decreased synaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. Meanwhile, the opioid antagonist naloxone increased the density of spines. Chronic treatment with morphine decreased the density of dendritic spines even in the presence of Tetrodotoxin, a sodium channel blocker, indicating that the morphine's effect was not caused by altered activity in neural network through suppression of GABA release. The effect of morphine on dendritic spines was absent in transgenic mice lacking MORs and was blocked by CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-ThrNH2), a mu-receptor antagonist. These data together with others suggest that endogenous opioids and/or constitutive activity of MORs participate in maintaining normal morphology and function of spines, challenging the classical model of opioids. Abnormal alteration of spines may occur in drug addiction when opioid receptors are overactivated by exogenous opiates.
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111
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DeHaven-Hudkins DL, Dolle RE. Peripherally restricted opioid agonists as novel analgesic agents. Curr Pharm Des 2004; 10:743-57. [PMID: 15032700 DOI: 10.2174/1381612043453036] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mediation of antinociception via opioid receptors located in the periphery is a viable strategy to produce analgesia without the occurrence of side effects associated with stimulation of opioid receptors located in the central nervous system. Peripheral opioid receptors are particularly important in inflammatory pain states and in the responses to pruritogenic stimuli, and have been implicated in the transmission of visceral pain. Medicinal chemistry approaches to achieve peripheralization of opioid agonists have started with a centrally acting opioid agonist as a template, and introduced features of lipophilicity, hydrophilicity, or combined lipophilicity and hydrophilicity to achieve amphiphilicity. Quaternarization of centrally acting opioid agonists or identification of compounds that serve as substrates for the mdr transporter to achieve transport out of the brain has also been employed. The in vivo assays used to identify peripherally selective compounds have measured a variety of behavioral and pharmacokinetic endpoints, with varying degrees of predictability. This review focuses on a discussion of these methods, as well as a review of those compounds where sufficient data exist to support a claim of peripheralization in vivo.
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MESH Headings
- Analgesics, Opioid/chemical synthesis
- Analgesics, Opioid/pharmacokinetics
- Analgesics, Opioid/pharmacology
- Animals
- Drug Design
- Humans
- Molecular Conformation
- Pain Measurement/drug effects
- Peripheral Nerves/drug effects
- Receptors, Opioid/agonists
- Receptors, Opioid, delta/agonists
- Receptors, Opioid, delta/chemistry
- Receptors, Opioid, kappa/agonists
- Receptors, Opioid, kappa/chemistry
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/chemistry
- Structure-Activity Relationship
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112
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Han W, Ide S, Sora I, Yamamoto H, Ikeda K. A Possible Genetic Mechanism Underlying Individual and Interstrain Differences in Opioid Actions: Focus on the Mu Opioid Receptor Gene. Ann N Y Acad Sci 2004; 1025:370-5. [PMID: 15542738 DOI: 10.1196/annals.1307.045] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Individual differences in responses to opioids limit effective pain treatment with these drugs. Identifying the mechanism could help to improve the analgesic effects of them. Since the molecular cloning of the mu opioid receptor (muOR) gene, substantial advances in opioid research have been made, including the discoveries that muOR plays a mandatory role in the analgesic effects of opioids and that the sequence of the muOR gene varies from one individual to another. It is conceivable that the differences in the muOR gene cause individual differences in opioid actions. The present review summarizes the recent advances made in research on human and mouse muOR genes and proposes that the variances in the 3' untranslated region (39-UTR) of the muOR gene might participate in the variability of the opioid response.
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MESH Headings
- Animals
- Humans
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C57BL
- Narcotics/metabolism
- Receptors, Opioid, mu/biosynthesis
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/physiology
- Species Specificity
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113
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Cadet P, Rasmussen M, Zhu W, Tonnesen E, Mantione KJ, Stefano GB. Endogenous morphinergic signaling and tumor growth. FRONT BIOSCI-LANDMRK 2004; 9:3176-86. [PMID: 15353348 DOI: 10.2741/1471] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mu3 opiate receptor subtype has been characterized by various binding assays as opiate alkaloid selective (e.g. morphine) and opioid peptide (e.g. methionine enkephalin) insensitive. This opiate receptor subtype has been found on human, including cancer cell lines, and invertebrate tissues, demonstrating that it has been conserved during evolution. Furthermore, in numerous reports, this receptor is coupled to constitutive nitric oxide release. In this regard, for example, morphine immune down regulating activities parallels those actions formerly attributed to nitric oxide. We have now identified the mu3 receptor at the molecular level and sequence analysis of the isolated cDNA suggests that it is a novel, alternatively spliced variant of the mu opiate receptor gene (MOR). Furthermore, using Northern blot, reverse transcription coupled to polymerase chain reaction (RT-PCR) and sequence analysis, we have demonstrated the expression of this new mu variant in human vascular tissue, mononuclear cells, polymorphonuclear cells, and human neuroblastoma cells. The presence of this mu splice variant, adds to the growing body of evidence supporting the hypothesis that morphine is an endogenous signaling molecule in neural, immune and vascular systems. In addition to their use in the treatment of pain, opioid peptides appear to be important in the growth regulation of normal and neoplastic tissue. This review will focus on the influence of opiate alkaloids, e.g., morphine, on tumor growth, with emphasis on immuno-regulatory and antiproliferative mechanisms.
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MESH Headings
- Alternative Splicing
- Animals
- Apoptosis
- Blotting, Northern
- COS Cells
- Cell Line, Tumor
- Cell Proliferation
- Chlorocebus aethiops
- Cloning, Molecular
- DNA, Complementary/metabolism
- Gene Library
- Humans
- Killer Cells, Natural/metabolism
- Macrophages/metabolism
- Male
- Morphine/metabolism
- Neoplasms/metabolism
- Neoplasms/pathology
- Neuroblastoma/metabolism
- Neutrophils/metabolism
- Nitric Oxide/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Signal Transduction
- Testis/metabolism
- Transcription, Genetic
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114
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Fowler CB, Pogozheva ID, LeVine H, Mosberg HI. Refinement of a homology model of the mu-opioid receptor using distance constraints from intrinsic and engineered zinc-binding sites. Biochemistry 2004; 43:8700-10. [PMID: 15236578 DOI: 10.1021/bi036067r] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Publication of the rhodopsin X-ray structure has facilitated the development of homology models of other G protein-coupled receptors. However, possible shifts of transmembrane (TM) alpha helices, expected variations in helical distortions, and differences in loop size necessitate experimental verification of these comparative models. To refine a rhodopsin-based homology model of the mu-opioid receptor (MOR), we experimentally determined structural-distance constraints from intrinsic and engineered metal-binding sites in the rat MOR. Investigating the relatively high intrinsic affinity of MOR for Zn(2+) (IC(50) approximately 30microM), we observed that mutation of His(319) (TM7) abolished Zn(2+) inhibition of ligand binding, while mutation of Asp(216) (extracellular loop 2) decreased the effect of Zn(2+), suggesting these residues participate in the intrinsic Zn(2+)-binding center of MOR. To verify the relative orientation of TM5 and TM6 and to examine whether a rhodopsin-like alpha aneurism is present in TM5, we engineered Zn(2+)-binding centers by mutating residues of TM5 and TM6 to Cys or His, making use of the native His(297) in TM6 as an additional Zn(2+)-coordination site. Inhibition of opioid ligand binding by Zn(2+) suggests that residues Ile(234) and Phe(237) in TM5 face the binding-site crevice and form a metal-binding center with His(297) and Val(300) in TM6. This observation is inconsistent with a rhodopsin-like structure, which would locate Ile(234) on the lipid-exposed side of TM5, too distant from other residues making up the Zn(2+)-binding site. Subsequent distance geometry refinement of the MOR model indicates that the rhodopsin-like alpha aneurism is likely absent in TM2 but present in TM5.
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115
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Rodgers G, Hubert C, McKinzie J, Suter T, Statnick M, Emmerson P, Stancato L. Development of displacement binding and GTPgammaS scintillation proximity assays for the identification of antagonists of the micro-opioid receptor. Assay Drug Dev Technol 2004; 1:627-36. [PMID: 15090235 DOI: 10.1089/154065803770380986] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
This article describes the development of micro-opioid receptor (MOR) binding and GTPgammaS functional SPAs as improved screening tools for the identification of MOR antagonists. Opioid receptors are members of the seven-transmembrane G protein-coupled receptor (GPCR) family and are involved in the control of various aspects of human physiology, including pain, stress, reward, addiction, respiration, gastric motility, and pituitary hormone secretion. Activation of the MOR initiates intracellular signaling pathways leading to a reduction in intracellular cyclic AMP levels, inhibition of calcium channels, and activation of potassium channels resulting in a reduction of the excitability of neurons. Characterization of opioid receptor ligand binding has traditionally been accomplished through the use of low throughput filtration-based binding assays, whereas functional activity has been based upon cyclic AMP measurements or filtration-based GTPgammaS functional assays. This report describes the development of a MOR displacement binding SPA using the radiolabeled antagonist [(3)H]diprenorphine ((3)H-DPN). The assay was optimized using statistical experimental design and demonstrates the stability and robustness necessary for HTS. The assay was biased toward the identification of MOR antagonists through the addition of Na(+). Our assay conditions also minimized the phenomenon of ligand depletion, a problem commonly observed in low-volume assays using high receptor-expressing cell lines. The optimized procedure revealed (3)H-DPN affinity constants at the MOR that were consistent with results obtained using filtration methods (K(D) (SPA) = 1.89 +/- 0.24 nM, K(D) (filtration) = 1.88 +/- 0.35 nM). The binding SPA identified known opioid receptor modulators contained within the Library of Pharmacological Active Compounds (LOPAC) cassette, and the GTPgammaS scintillation proximity assay (SPA) was used to confirm the functional activity of the LOPAC antagonists acting at the MOR. Conversion of the ligand binding and GTPgammaS functional assays to a homogeneous SPA generated a simple assay with dramatically increased throughput. Data from the development and implementation of the displacement binding and GTPgammaS functional SPAs are presented.
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116
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Gomes I, Gupta A, Filipovska J, Szeto HH, Pintar JE, Devi LA. A role for heterodimerization of mu and delta opiate receptors in enhancing morphine analgesia. Proc Natl Acad Sci U S A 2004; 101:5135-9. [PMID: 15044695 PMCID: PMC387386 DOI: 10.1073/pnas.0307601101] [Citation(s) in RCA: 335] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Opiates such as morphine are the choice analgesic in the treatment of chronic pain. However their long-term use is limited because of the development of tolerance and dependence. Due to its importance in therapy, different strategies have been considered for making opiates such as morphine more effective, while curbing its liability to be abused. One such strategy has been to use a combination of drugs to improve the effectiveness of morphine. In particular, delta opioid receptor ligands have been useful in enhancing morphine's potency. The underlying molecular basis for these observations is not understood. We propose the modulation of receptor function by physical association between mu and delta opioid receptors as a potential mechanism. In support of this hypothesis, we show that mu-delta interacting complexes exist in live cells and native membranes and that the occupancy of delta receptors (by antagonists) is sufficient to enhance mu opioid receptor binding and signaling activity. Furthermore, delta receptor antagonists enhance morphine-mediated intrathecal analgesia. Thus, heterodimeric associations between mu-delta opioid receptors can be used as a model for the development of novel combination therapies for the treatment of chronic pain and other pathologies.
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117
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Celver J, Xu M, Jin W, Lowe J, Chavkin C. Distinct domains of the mu-opioid receptor control uncoupling and internalization. Mol Pharmacol 2004; 65:528-37. [PMID: 14978231 DOI: 10.1124/mol.65.3.528] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Homologous desensitization of the micro opioid receptor (muOR) can be resolved into distinct processes that include the uncoupling of the muOR from its G-protein effectors and internalization of cell surface receptors. Using electrophysiological recordings of muOR activation of G-protein-coupled K+ channels (Kir3) in Xenopus laevis oocytes and AtT20 cells, confocal microscopy of receptor localization, and radioligand binding of cell surface receptors, we resolved these desensitization mechanisms to determine the domain of muOR important for receptor uncoupling. Activation of muOR by saturating concentrations of [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), methadone, or fentanyl, but not morphine, produced robust internalization of a green fluorescent protein-tagged muOR. A subsaturating concentration of DAMGO (100 nM) did not cause receptor internalization but markedly reduced the subsequent responsiveness of Kir3 by uncoupling muOR. muOR desensitization in AtT20 cells was confirmed to be homologous, because desensitization by 100 nM DAMGO was blocked by dominant-negative forms of either G protein-coupled receptor kinase (GRK) or arrestin, and pretreatment with DAMGO did not affect the Kir3 response to somatostatin receptor activation. Alanine substitution of a single threonine in the second cytoplasmic loop of the muOR (Threonine 180) blocked agonist-dependent receptor uncoupling without affecting receptor internalization. These results suggest that GRK-dependent phosphorylation of muOR required threonine 180 for uncoupling but that a different GRK and arrestin-dependent mechanism controlled muOR internalization in AtT20 cells.
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118
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Cox BM, Crowder AT. Receptor domains regulating mu opioid receptor uncoupling and internalization: relevance to opioid tolerance. Mol Pharmacol 2004; 65:492-5. [PMID: 14978226 DOI: 10.1124/mol.65.3.492] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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119
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Christoffers KH, Li H, Keenan SM, Howells RD. Purification and mass spectrometric analysis of the mu opioid receptor. ACTA ACUST UNITED AC 2004; 118:119-31. [PMID: 14559361 DOI: 10.1016/j.molbrainres.2003.08.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A mouse mu opioid receptor was engineered to contain a FLAG epitope at the amino-terminus and a hexahistidine tag at the carboxyl-terminus to facilitate purification. Selection of transfected human embryonic kidney (HEK) 293 cells yielded a cell line that expressed the receptor with a B(max) of 10 pmol/mg protein. 3[H]Bremazocine exhibited high affinity binding to the epitope-tagged mu opioid receptor with a KD of 1.0 nM. The agonists [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), morphine and [D-Ala(2),D-Leu(5)]enkephalin (DADL) competitively inhibited bremazocine binding to the tagged mu receptor with KI's of 3.5, 17 and 70 nM, respectively. Chronic treatment of cells expressing the epitope-tagged mu receptor with DAMGO resulted in down-regulation of the receptor, indicating that the tagged receptor retained the capacity to mediate signal transduction. The mu receptor was solubilized from HEK 293 cell membranes with n-dodecyl-beta-D-maltoside in an active form that maintained high affinity bremazocine binding. Sequential use of wheat germ agglutinin (WGA)-agarose chromatography, Sephacryl S300 gel filtration chromatography, immobilized metal affinity chromatography, immunoaffinity chromatography, and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) permitted purification of the receptor. The purified mu opioid receptor was a glycoprotein that migrated on SDS/PAGE with an apparent molecular mass of 80 kDa. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry was used to identify and characterize peptides derived from the mu opioid receptor following in-gel digestion with trypsin or chymotrypsin, and precursor-derived tandem mass spectrometry (ms/ms) confirmed the identity of several peptides derived from enzymatic digestion of the mu opioid receptor.
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120
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Kvam TM, Baar C, Rakvåg TT, Kaasa S, Krokan HE, Skorpen F. Genetic analysis of the murine mu opioid receptor: increased complexity of Oprm gene splicing. J Mol Med (Berl) 2004; 82:250-5. [PMID: 14991152 DOI: 10.1007/s00109-003-0514-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2003] [Accepted: 11/03/2003] [Indexed: 11/30/2022]
Abstract
Evidence exists that mu analgesics such as morphine, methadone and fentanyl may act through distinct mu opioid receptor mechanisms. It has been proposed that the functional diversity of mu opioid receptors may be related to alternative splicing of the Oprm gene. Although a number of mu opioid receptor mRNA splice variants have been reported, their biological relevance has been controversial, due in part to their very low abundance and a general lack of validation from independent laboratories. We have identified 11 of 17 proposed exons as well as the majority of exon combinations used to make 21 differentially spliced Oprm mRNAs from mouse whole brain cDNA, using polymerase chain reaction (PCR) conditions different from those used by the single other group that has reported multiple splice forms. Alternative splicing was shown to occur at both the 5' and 3' termini. Moreover, verification of a short variant, containing exons 1 and 4 only, suggests that splicing also occurs directly between 5' and 3' exons. Notably, a novel splice variant, MOR-1T, demonstrates for the first time that exon 4 can be used in combination with further downstream exons to make the 3'-end of MOR-1 splice variants. The putative protein encoded by MOR-1T is predicted to be identical to that of MOR-1, implying that the MOR-1 protein can be generated from at least five differentially spliced mRNAs. Our results support the view that the Oprm gene undergoes extensive alternative splicing, as a likely major contributor to the diversity of mu opioid receptors.
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121
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Miller GM, Bendor J, Tiefenbacher S, Yang H, Novak MA, Madras BK. A mu-opioid receptor single nucleotide polymorphism in rhesus monkey: association with stress response and aggression. Mol Psychiatry 2004; 9:99-108. [PMID: 14699447 DOI: 10.1038/sj.mp.4001378] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Variations in the human mu-opioid receptor gene have driven exploration of their biochemical, physiological and pathological relevance. We investigated the existence of variations in the nonhuman primate mu-opioid receptor gene to determine whether nonhuman primates can model genotype/phenotype associations of relevance to humans. Similar to the A118G single nucleotide polymorphism (SNP) in the human mu-opioid receptor gene, a SNP discovered in the rhesus monkey mu-opioid receptor gene (C77G) alters an amino acid in the N-terminal arm of the receptor (arginine for proline at position 26). Two mu-opioid receptor coding regions isolated from a single heterozygous (C77/G77) rhesus monkey brain were expressed in HEK-293 cells and characterized in radioreceptor assays. Paralleling the findings of increased affinity of beta-endorphin by the A118G allele in the human, the rhesus monkey mu-opioid receptor protein derived from the G77-containing clone demonstrated a 3.5-fold greater affinity for beta-endorphin than the receptor derived from the C77-containing clone. An assay developed to assess the incidence of the C77G SNP in a behaviorally and physiologically characterized cohort of rhesus monkeys (n=32) indicated that 44% were homozygous for C77-containing alleles, 50% were heterozygous and 6% were homozygous for G77-containing alleles. The presence of G77-containing alleles was associated with significantly lower basal and ACTH-stimulated plasma cortisol levels (P<0.03-0.05 and P<0.02, respectively) and a significantly higher aggressive threat score (P<0.05) in vivo. In a cohort of 20 monkeys, a trend towards an inverse correlation between aggressive threat and plasma cortisol levels was observed. The findings suggest that mu-opioid receptor haplotypes in monkeys can contribute to individual variability in stress response and related aggression. The data support the use of nonhuman primates to investigate mu-opioid receptor genotype/phenotype relations of relevance to humans.
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122
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Malicka J, Czaplewski C, Groth M, Wiczk W, Oldziej S, Lankiewicz L, Ciarkowski J, Liwo A. Use of NMR and Fluorescence Spectroscopy as well as Theoretical Conformational Analysis in Conformation-activity Studies of Cyclic Enkephalin Analogues. Curr Top Med Chem 2004; 4:123-33. [PMID: 14754380 DOI: 10.2174/1568026043451591] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In this review the conformational studies of natural enkephalins (H-Tyr-Gly-Gly-Phe-Met-OH; the [Met(5)]enkephalin and H-Tyr-Gly-Gly-Phe-Leu-OH; the [Leu(5)]enkephalin), their acyclic and cyclic analogues, including those carried out in our laboratory, performed by experimental and theoretical methods and their combination, are described. Emphasis is given on the role of conformational constraints introduced by cyclization on activity at the micro and delta opioid receptors. Comparison of the conformations of cyclic enkephalin analogues with high delta-receptor activity with those of potent rigid non-peptide delta-receptor agonists indicates that the proximity of the aromatic side chains in positions 1 and 4 as well as the N-terminal amino group is desirable for the activity at the delta opioid receptors; early conformational studies also suggested that spatial separation of the aromatic side chains and rigidity of the cyclic backbone is desirable for micro-receptor activity. The results of our recent conformational studies performed with the use of fluorescence and NMR spectroscopy as well as theoretical calculations indicate, however, that these structural features are not necessary for activity at the micro opioid receptors. Methods applied to the determination of the conformation of flexible peptides, such as Nuclear Magnetic Resonance (NMR), fluorescence spectroscopy, and theoretical conformational analysis are also discussed briefly.
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MESH Headings
- Enkephalins/chemistry
- Enkephalins/metabolism
- Magnetic Resonance Spectroscopy/methods
- Models, Molecular
- Peptides, Cyclic/chemistry
- Peptides, Cyclic/metabolism
- Protein Conformation
- Receptors, Opioid, delta/chemistry
- Receptors, Opioid, delta/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/metabolism
- Spectrometry, Fluorescence/methods
- Structure-Activity Relationship
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123
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Beigi F, Wainer IW. Syntheses of Immobilized G Protein-Coupled Receptor Chromatographic Stationary Phases: Characterization of Immobilized μ and κ Opioid Receptors. Anal Chem 2003; 75:4480-5. [PMID: 14632053 DOI: 10.1021/ac034385q] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Opioid receptors are members of the superfamily of G protein-coupled receptors (GPCRs). Liquid chromatographic stationary phases containing either the human mu or kappa opioid receptor subtypes have been developed to study the binding between the opioid receptors and their ligands. The receptors were obtained from Chinese hamster ovary cells stably transfected with human mu or kappa receptor subtypes. The receptors were isolated through partial solubilization with sodium cholate detergent, and the partially purified receptor complex was immobilized in the phospholipid analogue monolayer of an immobilized artificial membrane liquid chromatographic stationary phase. The resulting phase was packed into a glass column (1.8 x 0.5 (i.d.) cm) and used in the on-line chromatographic determination of drug/ligand binding affinities to the immobilized opioid receptors. Preliminary on-line binding studies employing frontal chromatographic techniques were conducted with the known mu antagonist (naloxone) and a kappa agonist (U69593). The calculated dissociation constants (Kd) were 110 nM for naloxone and 84 nM for U69593. The results indicate that the immobilized receptors retained their ability to specifically bind ligands and were active for 1200 column volumes applied over two weeks. Zonal chromatographic experiments were also conducted, and competitive displacements of the marker ligands were observed. The results suggest that the immobilized opioid receptor stationary phases can be used to qualitatively assess the binding affinities of compounds to the immobilized receptors and represent the first example of the use of immobilized GPCRs in a chromatographic system.
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MESH Headings
- Animals
- Binding Sites
- CHO Cells
- Chromatography, Affinity/methods
- Cricetinae
- Female
- Gene Expression Regulation
- Humans
- Ligands
- Naloxone/pharmacology
- Receptors, Opioid, kappa/chemistry
- Receptors, Opioid, kappa/genetics
- Receptors, Opioid, kappa/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
- Solubility
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124
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Feng GJ, Kellett E, Scorer CA, Wilde J, White JH, Milligan G. Selective interactions between helix VIII of the human mu-opioid receptors and the C terminus of periplakin disrupt G protein activation. J Biol Chem 2003; 278:33400-7. [PMID: 12810704 DOI: 10.1074/jbc.m305866200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Analysis of interactions between the C-terminal tail of the MOP-1 and MOP-1A variants of the human mu-opioid receptor with proteins derived from a human brain cDNA library resulted in identification of the actin and intermediate filament-binding protein periplakin. Mapping of this interaction indicated that the predicted fourth intracellular loop/helix VIII of the receptor interacts with the C-terminal rod and linker region of periplakin. Periplakin is widely expressed in the central nervous system of both man and rat and demonstrated an overlapping but not identical distribution with mu-opioid (MOP) receptors. Co-expression of periplakin with MOP-1 or a MOP-1-eYFP fusion construct in HEK293 cells did not interfere with agonist-mediated internalization of the receptor. When co-expressed with a MOP-1-Gi1 alpha fusion protein periplakin significantly reduced the capacity of the agonist to stimulate binding of 35S-labeled guanosine 5'-3-O-(thio)triphosphate ([35S]GTP gamma S) to the receptor-associated G protein. By contrast, periplakin did not interfere with agonist-stimulation of [35S]GTP gamma S binding to either an alpha 2A-adrenoreceptor-Gi1 alpha fusion protein or a beta2-adrenoreceptor-Gs alpha fusion protein, indicating its selectivity of function. This represents the first example of an opioid receptor-interacting protein that functions to disrupt agonist-mediated G protein activation.
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MESH Headings
- Actins/chemistry
- Amino Acid Sequence
- Biotin/pharmacology
- Brain/metabolism
- Cell Line
- Cell Membrane/metabolism
- Central Nervous System/metabolism
- Cytoskeletal Proteins/chemistry
- DNA/metabolism
- DNA, Complementary/metabolism
- GTP-Binding Proteins/metabolism
- Gene Library
- Glutathione Transferase/metabolism
- Guanosine 5'-O-(3-Thiotriphosphate)/metabolism
- Histidine/chemistry
- Humans
- Immunoblotting
- Ligands
- Microscopy, Confocal
- Microscopy, Fluorescence
- Molecular Sequence Data
- Plakins
- Protein Binding
- Protein Isoforms
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/metabolism
- Recombinant Fusion Proteins/metabolism
- Sequence Homology, Amino Acid
- Tissue Distribution
- Transfection
- Two-Hybrid System Techniques
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125
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Chaipatikul V, Loh HH, Law PY. Ligand-selective activation of mu-oid receptor: demonstrated with deletion and single amino acid mutations of third intracellular loop domain. J Pharmacol Exp Ther 2003; 305:909-18. [PMID: 12626655 DOI: 10.1124/jpet.102.046219] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mechanism for the differential regulation of the mu-opioid receptor by agonists is investigated by identifying the receptor domains used to define the relative efficacies of three mu-opioid receptor-selective agonists: [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), morphine, and [N-MePhe3,D-Pro4]-morphiceptin (PL017) to inhibit forskolin-stimulated intracellular cAMP production in human embryonic kidney 293 cells. This was accomplished by systematically deleting four to five amino acids clusters within the third intracellular loop of rat mu-opioid receptor, Arg258 to Arg280, followed by Ala substitution and scanning studies of the 276RRITR280 sequence, the putative G protein-coupling motif. Deletion of the four to five amino acid clusters resulted in differential effects on the affinities of the agonists and antagonists, and also on the potencies and coupling efficiencies of the three opioid agonists. Ala scanning studies of the 276RRITR280 sequence revealed also the differences between [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), morphine, and PL017. Substitution of Arg276 or Ile278 with Ala reduced the potency of DAMGO but not that of morphine PL017. Meanwhile, mutation of Thr279 to Ala increased the potencies of morphine and PL017 but not that of DAMGO. The I278A mutation decreased the DAMGO coupling efficiency but increased the PL017 coupling efficiency. The R280A mutation resulted in the increase in PL017 potency and coupling efficiency without altering those of DAMGO and morphine. Thus, these mutation studies suggested that the activation of mu-opioid receptor and interaction between the critical domains such as RRITR within third intracellular loop and the G proteins are agonist-selective.
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MESH Headings
- Adenylyl Cyclases/metabolism
- Alanine/metabolism
- Analgesics, Opioid/pharmacology
- Cells, Cultured
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacology
- Enkephalins/pharmacology
- Gene Deletion
- Humans
- Membrane Proteins/chemistry
- Membrane Proteins/drug effects
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Morphine/pharmacology
- Narcotic Antagonists/pharmacology
- Pertussis Toxin/pharmacology
- Protein Structure, Tertiary
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/drug effects
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
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