Immunoaffinity-purified opiate receptor specifically binds the delta-class opiate receptor ligand, cis-(+)-3-methylfentanylisothiocyanate, SUPERFIT

Developmental expression of mu and delta opioid receptors in the rat brainstem: evidence for a postnatal switch in mu isoform expression

Opioid receptors are expressed in the brain during fetal and postnatal development, and the expression patterns vary with developmental age. To investigate the role of opioids in brain development, immunoblotting and immunohistochemical techniques were used to determine mu (MOR) and delta (DOR) opioid receptor expression levels and regional distributions in fetal, early postnatal and adult rat brainstem. Two immunoreactive bands were seen on Western blots of brainstem lysates for both MOR (50 and 70 kDa) and DOR (30 and 60 kDa). The expression levels of the isoforms changed dramatically between 6 and 15 days after birth. Total MOR protein was expressed at low levels in fetal and early postnatal animals with the 50-kDa band predominating. MOR expression then increased in the older animals and the 70-kDa isoform became dominant. Total DOR protein showed the opposite pattern, being high in the fetal and neonatal brainstem and low in the juvenile and adult. A postnatal switch in isoform expression for DOR was not evident in our study. In general, regional brainstem distributions in developing and adult animals were comparable to those reported in the literature, and both receptors were localized in the same areas where opioid receptor expression was high. It was concluded that MOR and DOR are developmentally regulated in the brainstem of the rat, that the isoform ratio switches postnatally from a fetal-neonatal pattern to a juvenile-adult pattern and that both receptors are generally expressed in the same brainstem regions from E16 to adult.

Conformational study of [Met5]enkephalin-Arg-Phe in the presence of phosphatidylserine vesicles

The interaction of [Met5]enkephalin-Arg.Phe with phosphatidylserine (PtdSer) was studied by circular dichroism (CD), two-dimensional nuclear magnetic resonance spectroscopy, hybrid distance geometry simulated annealing (DG-SA) and molecular dynamics (MD) calculations. The very low solubility of [Met5]enkephalin-Arg-Phe and the instability of the solution containing PtdSer vesicles at low pH values did not allow us to observe the amide proton resonances in the usual two-dimensional NMR work. NOESY cross-peaks of protons of side chains from two-dimensional NMR were converted into distances which were used as restraints for modelling with DG-SA and MD. Our results indicate that, in aqueous solutions at pH 7.68 [Met5]enkephalin-Arg-Phe exists in the absence of PtdSer as a random distribution of conformers, whereas in the presence of PtdSer it adopts conformations containing a common orientation of the bonds of C alpha 2, C alpha 3, C alpha 4, and C alpha 5, although different orientations of the peptide planes are consistent with the results. Two of the reported conformers from MD simulations are characterized by the presence of a 2<--4 gamma and inverse gamma turns centered on Gly3. A gradual decline of order was observed when moving from the central moiety of the peptide to both the N-terminus and C-terminus. Finally, the DG-SA and MD calculations resulted in a structure such that the orientation of the Phe4 and Met5 side chains favours hydrophobic interactions with the apolar portion of the PtdSer vesicle to form a hydrophobic cluster. These data support the hypothesis of a role of lipids to modify the conformation of [Met5]enkephalin-Arg-Phe to permit the interactions with the receptor site.

The antisense homology box: a new motif within proteins that encodes biologically active peptides

Amphiphilic peptides approximately fifteen amino acids in length and their corresponding antisense peptides exist within protein molecules. These regions (termed antisense homology boxes) are separated by approximately fifty amino acids. Because many sense-antisense peptide pairs have been reported to recognize and bind to each other, antisense homology boxes may be involved in folding, chaperoning and oligomer formation of proteins. The antisense homology box-derived peptide CALSVDRYRAVASW, a fragment of human endothelin A receptor, proved to be a specific inhibitor of endothelin peptide (ET-1) in a smooth muscle relaxation assay. The peptide was able to block endotoxin-induced shock in rats as well. Our finding of endothelin receptor inhibitor among antisense homology box-derived peptides indicates that searching proteins for this new motif may be useful in finding biologically active peptides.

Purification to homogeneity of an active opioid receptor from rat brain by affinity chromatography

Active opioid binding proteins were solubilized from rat brain membranes in high yield with sodium deoxycholate in the presence of NaCl. Purification of opioid binding proteins was accomplished by opioid antagonist affinity chromatography. Chromatography using the delta-opioid antagonist N,N-diallyl-Tyr-D-Leu-Gly-Tyr-Leu attached to omega-aminododecyl-agarose (Affi-G) (procedure A) yielded a partially purified protein that binds selectively the delta-opioid agonist [3H]Tyr-D-Ser-Gly-Phe-Leu-Thr ([3H]DSLET), with a Kd of 19 +/- 3 nM and a Bmax of 5.1 +/- 0.4 nmol/mg of protein. Subsequently, Lens culinaris agglutinin-Sepharose 4B chromatography of the Affi-G eluate resulted in isolation of an electrophoretically homogeneous protein of 58 kDa that binds selectively [3H]DSLET with a Kd of 21 +/- 3 nM and a Bmax of 16.5 +/- 1.0 nmol/mg of protein. Chromatography using the nonselective antagonist 6-aminonaloxone coupled to 6-aminohexanoic acid-Sepharose 4B (Affi-NAL) (procedure B) resulted in isolation of a protein that binds selectively [3H]DSLET with a Kd of 32 +/- 2 nM and a Bmax of 12.4 +/- 0.5 nmol/mg of protein, and NaDodSO4/PAGE revealed a major band of apparent molecular mass 58 kDa. Polyclonal antibodies (Anti-R IgG) raised against the Affi-NAL protein inhibit the specific [3H]DSLET binding to the Affi-NAL eluate and to the solubilized membranes. Moreover, the Anti-R IgG inhibits the specific binding of radiolabeled Tyr-D-Ala-Gly-N-methyl-Phe-Gly-ol (DAMGO; mu-agonist), DSLET (delta-agonist), and naloxone to homogenates of rat brain membranes with equal potency. Furthermore, immunoaffinity chromatography of solubilized membranes resulted in the retention of a major protein of apparent molecular mass 58 kDa. In addition, immunoblotting of solubilized membranes and purified proteins from the Affi-G and Affi-NAL matrices revealed that the Anti-R IgG interacts with a protein of 58 kDa.

Technical aspects of opioid receptor localization: detection of opioid receptor proteins by immunocytochemistry or with a biotinylated dynorphin analog

Opioid receptors were localized at the cellular level, using either anti-opioid receptor antibodies or a biotinylated opioid ligand. In addition, a simple method was developed for selection of second antisera on their potencies to detect particular monoclonal antibodies (mAbs). Most anti-opioid receptor antibodies tested were not able to recognize the opioid receptor in frozen or fixed tissue sections, which was in contrast with their ability to recognize opioid receptors in isolated membrane fractions. However, one batch of anti-idiotypic mAbs gave a good immunocytochemical staining. Distribution of immunoreactivity suggested that these antibodies recognized more than one opioid receptor subtype. After very short fixation times, staining with a biotinylated kappa-selective ligand (DAKLIB) could be observed in the neural and intermediate lobe of pituitary. This binding could be displaced by non-biotinylated DAKLI. The pattern of DAKLIB staining in the neural lobe had the appearance of binding to both nerve fibres and astrocytes. The present results show successful staining of tissue sections with anti-idiotypic antibodies and with a biotinylated ligand. The specificity is discussed in the light of control experiments, pharmacological data and previous studies.

Affinity cross-linked delta-opioid receptor in NG108-15 cells is low molecular weight (25 kDa) and coupled to GTP-binding proteins

The affinity cross-linking of the delta-opioid receptor in neuroblastoma x glioma NG108-15 cells was undertaken using (3-[125I]iodotyrosyl27)human-beta-endorphin ([125I]beta-endorphin) and disuccinimidyl suberate (DSS) or bis(sulfosuccinimidyl) suberate (BS3) in order to estimate molecular size. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, two radioactive bands were observed. Labeling of a major band of 29 kDa diminished in the presence of unlabeled selective delta-opioid agonist, [D-Pen2,D-Pen5]enkephalin (DPDPE), in a concentration-dependent manner, while labeling of a minor band of 58 kDa was hardly affected. The labeling intensity of the 29 kDa band decreased by addition of guanosine 5'-(3-o-thio)triphosphate (GTP gamma S) or by pretreatment of cells with pertussis toxin. These results, taking the molecular weight of covalently bound beta-endorphin (3.6 kDa) into consideration, suggest that the delta-opioid receptor in NG108-15 cell membrane is a 25 kDa protein which is coupled to pertussis toxin-sensitive guanosine triphosphate-binding proteins (G-proteins).

Complementary peptide to the carboxyl-terminal tetrapeptide of gastrin

Codons of noncoding DNA strands for peptides have been found to code for amino acids with hydropathic properties opposite to those of the native peptides. Synthetic peptides, designated as complementary peptides, with amino acid sequences coded by noncoding DNA strands of several peptide hormones have been shown to bind the native peptides. In some instances, antibodies to these complementary peptides have shown agonist or antagonist properties of the native hormones. In this study a peptide was synthesized based on codons complementary to messenger RNA for the carboxyl-terminal gastrin tetrapeptide. This complementary peptide bound radiolabeled human gastrin (G17). Antibodies to the complementary peptide competitively inhibited the binding of 125I-gastrin by canine fundic mucosal membrane preparations. These antibodies also showed gastrin agonist properties in that they stimulated canine gastric mucosal parietal cell [14C]aminopyrine uptake, used as an index of stimulation of gastric acid secretion. Competitive inhibition of 125I-gastrin binding by membrane receptors for gastrin and stimulation of [14C]-aminopyrine uptake by antibodies to the complementary peptide for the gastrin tetrapeptide are consistent with their recognition, binding, and occupancy of gastrin receptors.

Photoaffinity labelling of the mu-opioid receptor is dependent on the nature of the photosensitive group of carfentanil derivatives

Arylazido and aryldiazonium derivatives of carfentanil, bearing their photoactivatable function at the same position on the molecule, were synthesized. In the dark both of them exhibited similar binding affinity profiles and behaved as mu-selective and reversible ligands of the opioid receptor sites. Following irradiation, only the azido analog displayed the properties of an efficient, irreversible and selective label of the mu-opioid receptor, allowing physicochemical requirements for alkylation of this receptor subtype to be examined. Evidence is presented to consider this azido compound a promising tool for characterizing the mu-opioid receptor protein.

Bidirectional communication between the neuroendocrine and immune systems. Common hormones and hormone receptors

The results reviewed here support a molecular basis for bidirectional communication between the immune and neuroendocrine systems. The main findings can be summarized as follows: First, cells of the immune system can synthesize biologically active neuroendocrine peptide hormones. Second immune cells also possess receptors for many of these peptides. Third, these same neuroendocrine hormones can influence immune function; and fourth, lymphokines can influence neuroendocrine tissues. The interesting conceptual advance is the idea that the immune system may serve as a sensory organ. Thus, the immune system may sense stimuli that are not recognized by the central or peripheral nervous system. These stimuli are termed noncognitive and include bacteria, viruses, tumors and antigens. The recognition of such stimuli is converted into information in the form of lymphokines, monokines, and hormones and a message received by neuroendocrine tissues. On the other hand, nervous system recognition of stimuli can also be converted into chemical signals that can be relayed to immune cells resulting in physiological changes. On this basis, we predict that the pathophysiology associated with infectious agents may be related to the types and amounts of hormones produced by the immune system.

Monoclonal antibody against a peptide specified by [Met]-enkephalin complementary RNA recognizes the delta-class opioid receptor

Monoclonal antibodies (MAB) were developed which recognize a peptide, His-Glu-Ala-Pro-Ile (HEAPI), encoded by the RNA complementary to the mRNA specifying [Met]-enkephalin. One such MAB (designated 6193) exhibited a high degree of reactivity to the peptide sequence. Other characteristics of 6193 MAB include: the ability to block opioid ligand binding in a radioreceptor assay; agonist activity similar to opioid peptides in suppressing cAMP production; and the recognition of a 58 kDa protein on the surface of the neuroblastoma x glioma cell line, NG108-15. These results are consistent with a reactivity of 6193 MAB with the delta-class opioid receptor.

Complementary peptides as interactive sites for protein binding

The observation that pairs of peptides encoded from complementary strands of nucleic acids can bind one another suggested to us that proteins might use similar "complementary peptide" sequences to facilitate their interactions with other proteins or peptides. Here we review evidence to support this hypothesis. Investigations by us and by others showed that receptors and their ligands may use complementary peptide sequences or their analogs to facilitate binding. In addition, antibodies made against pairs of complementary peptides bind one another in an idiotypic/anti-idiotypic fashion. Taken together, these findings suggest that complementary peptide sequences may be used as recognition units by pairs of proteins which interact.

Evidence for a delta-class opioid receptor on cells of the immune system

Opioid receptors have been reported to be present on cells of the immune system. Both opioid receptor-ligand interactions which are reversible by naloxone (classical) and those interactions which are irreversible by naloxone (nonclassical) appear to alter various immunologic parameters through the ligand-receptor interactions. In an effort to characterize opioid receptors (which operate with classical interactions) on cells of the immune system, we employed the delta-class opioid receptor-specific ligand, cis-(+)-3-methylfentanylisothiocyanate (SUPERFIT). We herein report the specific labeling of a protein with a molecular weight of 70,000 Da under reducing conditions (58,000 Da under nonreducing conditions) from both B and T cell-enriched murine splenocytes and peripheral blood lymphocytes. Similar results are demonstrated by human peripheral blood lymphocytes and plastic-adherent (monocyte-enriched) leukocytes.

The production of antibodies which recognize opiate receptors on murine leukocytes

An antibody has been developed which recognizes opiate receptors on cells of the immune system. This antibody blocks specific binding of the radiolabeled opiate receptor ligand, 3H-dihydromorphine, to receptors on murine splenocytes. Additionally, the anti-receptor antibody competes with beta-endorphin, met-enkephalin, and naloxone for the same binding site on the leukocytes. Moreover, the anti-receptor antibody possesses agonist activity similar to beta-endorphin in suppressing cAMP production by lymphocytes. These results suggest the development of an antibody which recognizes classical opiate receptors on cells of the immune system.