Discrimination of a novel type of rat brain delta opioid receptors by enkephalin analog containing structurally constrained cyclopropylphenylalanine (inverted delta Phe)

Four different stereoisomers of cyclopropylphenylalanine (inverted delta Phe) were incorporated into [D-Ala2,Leu5]enkephalin at the position 4. These conformationally restricted enkephalin analogs were evaluated for their binding characteristics to mu and delta opioid receptors in rat brain. A striking finding is that the E-(2R,3S)-isomer binds to a novel class of delta receptors and discriminates this receptor from the ordinary delta receptor. This new type of delta receptor suspected to be a receptor which suppresses the thermal analgesia mediated through mu receptor. The Z-(2R,3R)-isomer was very potent with several times more enhanced affinity to delta receptors than to mu receptors, but could not differentiate the delta receptors. The Z-(2S,3S)-isomer was weak, and E-(2S,3R)-isomer was almost inactive.

Micellar electrokinetic chromatographic study of the interaction between enkephalin peptide analogs and charged micelles

The relative hydrophobicity/hydrophilicity of the pentapeptides leucine enkephalin (LE), methionine enkephalin (ME) and five analogs, differing in their uncharged side chain and/or chirality, was investigated by micellar electrokinetic capillary chromatography (MEKC) employing anionic and cationic surfactants. The effect of sodium dodecyl sulfate (SDS) concentration on peptide mobility was studied at pH 8.8, a value that is well above the peptide isoelectric point, to minimize electrostatic interaction with the anionic micelles. Similarly, the effect of cetyltrimethylammonium bromide (CTAB) cationic micelles on peptide migration was studied at pH 4.1. The migration order from MEKC experiments was compared to the peptide hydrophobicity calculated from reversed-phase HPLC-derived hydrophobicity coefficients. Although relative peptide hydrophobicity was, in general, positively correlated with effective electrophoretic mobility, a tryptophan-containing analog showed only weak interaction with micelles compared to the less hydrophobic peptides. The enkephalins studied were zwitterionic in character from pH 3 to 8, and their migration as a function of pH under MEKC conditions demonstrated that electrostatic forces were at least as important as hydrophobic interactions in pentapeptide-micelle complexation.

Gly(247)-->Asp proenkephalin A mutation is rare in schizophrenia populations

Schizophrenia is a complex and severe disorder of unknown cause and pathophysiology. In previous work examining an opioid hypothesis for schizophrenia, we identified a missense mutation (Gly(247)-->Asp) in the proenkephalin A gene of one African-American patient. In the current study involving an extended set of African-American and other patients, we sought to identify additional mutant alleles and to determine the distribution of these alleles among several racial groups. However, the Gly(247)-->Asp allele was not detected in any of 116 African-American (67 cases, 49 controls), 659 Caucasian, 1 Hispanic, 4 Asian, and 7 Native American individuals. Therefore, it appears that this mutation is a rare event of unknown clinical significance.

The structure of synenkephalin (pro-enkephalin 1-73) is dictated by three disulfide bridges

Mass spectrometry of fragments produced by limited proteolytic digestion of pro-enkephalin was used to locate the disulfide bridges in synenkephalin (pro-enkephalin 1-73), a domain which contains sorting information for targeting the pro-neuropeptide to the granules of the regulated secretory pathway in neuroendocrine cells. Mass spectrometric analysis was optimized by using chemicals that gave low interference with the ionization and desorption processes, and computer software which simplified the identification of all possible disulfide-linked peptide fragments. Three disulfide bridges between Cys2-Cys24, Cys6-Cys28, and Cys9-Cys41 were identified. Protein conformational prediction of synenkephalin1-42 shows beta-turns which facilitate the formation of these disulfide bonds.

Neoglycopeptide synthesis and purification in multi-gram scale: preparation of O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-N alpha-fluoren-9-yl-methoxycarbonyl-hydroxyproline and its use in the pilot-scale synthesis of the potent analgesic glycopeptide O1.5-beta-D-galactopyranosyl [DMet2, Hyp5]enkephalinamide

The preparation of a beta-galactosylated hydroxyproline derivative and its use in the multi-gram solid-phase synthesis of the potent analgesic neoglycopeptide O1.5-beta-D-galactopyranosyl [D-Met2, Hyp5]enkephalinamide is described in this paper. The most closely related impurities have been identified, isolated and characterized. Significant aspects of the synthesis and purification affecting yields and purity of both the building block and the target neoglycopeptide are discussed.

cDNA sequence and expression of bovine prodynorphin

Prodynorphin (ProDYN) in the anterior pituitary gland appears to be processed differently from the brain, and the ProDYN-derived peptides may function differently in the anterior pituitary than in the brain. To further investigate the roles of ProDYN-derived peptides in the anterior pituitary, we have determined the nucleotide (nt) sequence of the cDNA encoding bovine ProDYN. This is the first time a complete cDNA sequence for ProDYN has been reported. The nt and deduced amino acid (aa) sequences were compared to the known ProDYN of other species. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) combined with Southern blot analysis demonstrated that the expression of ProDYN in both the anterior and posterior pituitary glands was much lower than that in the neural tissues of the striatum and hypothalamus.

Structure-activity relationship of biphalin. The synthesis and biological activities of new analogues with modifications in positions 3 and 4

New analogues of biphalin [(Tyr-D-Ala-Gly-Phe-NH-)2] with modifications of amino acid residues in positions 3,3' and 4,4' have been synthesized. The potency and selectivity of these analogues were evaluated by competitive radioreceptor binding assay in the rat brain using [3H]CTOP (mu ligand) and [3H][p-Cl-Phe4]DPDPE (delta ligand) as ligands, and by bioassay in the mouse vas deferens (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay). The symmetrical substitution of phenylalanine in positions 4 and 4' with p-fluorophenylalanine or p-nitrophenylalanine resulted in an enhancement of the affinity at both delta and mu receptors, with some increase of the selectivity for delta opioid receptors. The analogue containing p-chlorophenylalanine in positions 4 and 4' is the most selective to the delta receptors in this series, with a selectivity ratio about 5. The symmetrical substitution of the glycine-3 residue with phenylalanine resulted in a decrease of binding affinities and biological potencies at both mu & delta receptors.

Combined use of NMR, distance geometry and MD calculations for the conformational analysis of opioid peptides of the type [D(L)-Cys2, D(L)-Cys5]enkephalin

The solution structures of a series of conformationally restricted pentapeptides with a sequence H-Tyr1-Cys2-Gly3-Phe4-Cys5-OH cyclic (2-5) disulfide, where the cysteines possess either the D or L configuration, were examined by a combined approach including NMR measurements as well as MD calculations. It turned out that at least one low energy conformer of H-Tyr1-D-Cys2-Gly3-Phe4-D-Cys5-OH cyclic (2-5) disulfide (DCDCE), as well as one conformer out of the group of calculated conformers for H-Tyr1-D-Cys2-Gly3-Phe4-Cys5-OH cyclic (2-5) disulfide (DCLCE), satisfies the NMR data obtained in this study, whereas for the derivative H-Tyr1-Cys2-Gly3-Phe4-Cys5-OH cyclic (2-5) disulfide, which contains solely L-Cys (LCLCE), there is no single structure compatible with the NMR data.

Solution conformation of [D-Pen2, D-Pen5] enkephalin in water: a NMR and molecular dynamics study

The solution conformation of [D-Pen2, D-Pen5] enkephalin (DPDPE), a highly potent delta-selective opioid agonist, was examined by means of NMR, molecular mechanics and molecular dynamics methods. The structural information in the solvent water was obtained employing one- and two-dimensional methods of 1H and 13C-NMR spectroscopy. Based on the distance geometry technique using the ROE data as input, 400 conformers were obtained and considered in the structure analysis. Alternatively, about 2000 conformers were stochastically generated and related to the NMR data after energy minimization. The structure analysis provides one conformer in agreement with all NMR data, which belongs to the lowest energy conformation group. This structure may serve as a reference conformer for DPDPE analogues synthesized with the aim of activity increase.

Development of a model for the delta-opioid receptor pharmacophore. 4. Residue 3 dehydrophenylalanine analogues of Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13) confirm required gauche orientation of aromatic side chain

We have previously proposed a model for the delta-opioid receptor binding conformation of the high affinity tetrapeptide Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13) based on experimental and theoretical conformational analysis of this peptide and a correlation of conformational preferences of further conformationally restricted analogues of this tetrapeptide with their receptor binding affinities. A key element of this model is the requirement that the Phe3 side chain exist in the chi 1 = -60 degrees conformation. Conformational calculations on the residue 3 dehydrophenylalanine analogues of JOM-13 suggest that while the dehydro (Z) phenylalanine analogue can be superimposed easily with the proposed binding conformer of JOM-13, the dehydro(E)phenylalanine analogue cannot. These results lead to the prediction that the dehydro(Z)phenylalanine analogue should display similar delta-receptor binding affinity as JOM-13 while the dehydro(E)phenylalanine analogue is expected to bind less avidly. Synthesis and subsequent opioid receptor binding analysis of the dehydrophenylalanine analogues of JOM-13 confirm these predictions, lending support to the delta-pharmacophore model.

Reversible affinity labeling of opioid receptors via disulfide bonding: discriminative labeling of mu and delta subtypes by chemically activated thiol-containing enkephalin analogs

The 3-nitro-2-pyridinesulfenyl (Npys) group bound to a mercapto group is a highly activated electrophilic reagent, which only reacts with a free mercapto group to form a disulfide bond via the thiol-disulfide exchange reaction. We incorporated the Npys group into enkephalin analogs to affinity label mu and delta opioid receptors. When rat brain membranes were incubated with [D-Ala2,Leu(CH2SNpys)5]enkephalin, and assayed for the inhibition of binding of DAGO and DSLET enkephalin analogs to opioid receptors, the number of receptors decreased sharply, depending upon the concentration of this SNpys-containing enkephalin. It was found that this enkephalin analog occupies mu receptors highly specifically (EC50 = 51 nM) and almost 100 times more selectively than delta receptors. In contrast, [D-Ala2,Leu5]enkephalyl-Cys(Npys)6 attached covalently to delta receptors (EC50 = 34 nM) about 150 times more selectively than to mu receptors. Although N-ethylmaleimide also inhibited the binding of DAGO and DSLET, four to six orders of magnitude higher concentrations were required as compared to SNpys-containing enkephalins. When enkephalin-bound rat membranes were treated with dithiothreitol, the loss of receptors was reversed, depending upon the concentration of and incubation time with dithiothreitol. The recovery was much faster (about 1,000 times) for delta receptors than for mu receptors. The present results indicated that both mu and delta receptors in rat brain consist of a free mercapto group near the enkephalin binding site and that SNpys-containing enkephalins can label these mercapto groups discriminatively. The disulfide bond between [D-Ala2,Leu5]enkephalyl-Cys6 and delta receptors appears to be exposed, while that between [D-Ala2,Leu(CH2-SNpys)5] enkephalin and mu receptors is shielded.

Comparison of cyclic delta-opioid peptides with non-peptide delta-agonist spiroindanyloxymorphone (SIOM) using the message-address concept: a molecular modeling study

Based upon the message-address concept, this molecular modeling study used the delta-selective agonist spiroindanyloxymorphone (SIOM) as a molecular template for a conformational search and analysis of delta-selective opioid peptides. It was assumed that the tyramine moiety plays the same role for delta-opioid receptor recognition in both peptide and non-peptide ligands. Using 20 reported low-energy conformations of Tyr-cyclo[D-Cys-D-Pen]-OH (JOM-13) for comparison, the geometrical relationship of the two aromatic rings present in SIOM was used for the identification of potential active conformations of JOM-13, from which two delta-receptor-binding models (I and II) were constructed. Models I and II differ from each other in the arrangement of the peptide backbones. To evaluate the two models, a conformational search of two other known delta-selective ligands, [D-Pen2,D-Pen5]enkephalin (DPDPE) and [D-Pen2,L-Pen5]enkephalin (DPLPE) was performed, using the geometrical relationship of the two aromatic rings defined in the two receptor-binding models as a molecular template. Among the conformations generated from the molecular simulation, low-energy conformers of DPDPE and DPLPE conforming to models I and II were identified. Unlike model I, conformers of DPDPE and DPLPE that fit model II contain a cis amide bond in the Gly3 residue.

Multivalent ligand system carrying enkephalin and neurotensin coimmobilized on liposomes

A multivalent ligand system was constructed by coimmobilization of two kinds of peptide ligands, enkephalin and neurotensin derivatives having a dioctadecyl group, on dimyristoylphosphatidylcholine (DMPC) liposomes. The enkephalin derivatives are Tyr-D-Ala-Gly-Trp-Leu-(Sar-Sar-Pro)n-[N(C18H37)2] (Enk3nD, n = 0, 1, 2), where a dioctadecyl group was connected to the C-terminal side of enkephalin directly or through a hydrophilic and flexible spacer chain of different lengths. The neurotensin derivatives are Ac-Glu[N(C18H37)2l-(Sar-Sar-Pro)n-Arg-Arg-Pro-Tyr-Ile-Leu-OH (D3nNT, n = 0, 1, 2, 3). The derivatives were spontaneously immobilized on DMPC liposomes by overnight incubation. The receptor affinity of the enkephalin derivatives became significantly higher upon immobilization on liposomes. The highest affinity was obtained for the delta receptor by Enk6D immobilized on DMPC liposomes. This affinity is higher than that of enkephalinamide. Neurotensin derivatives coimmobilized with large amounts of Enk3D on the DMPC liposomes show higher affinity than the neurotensin derivatives immobilized alone. The effect of Enk3D on the receptor affinity of the coimmobilized neurotensin derivative disappeared by the addition of [Ala2, MePhe4, Glyol5]enkephalin (DAGO). Therefore, the receptor affinity of a peptide hormone is altered by immobilization on DMPC liposomes and by coimmobilization with other peptide hormones. It was confirmed by fluorescent microscopy that the multivalent ligand system binds to receptors without release of the bound ligands from DMPC liposomes.

Opioid receptor affinity of multivalent ligand system consisting of polymerized liposome

A multivalent ligand system, in which enkephalin/phospholipid conjugates were immobilized on a polymerized liposome, has been prepared. A hydrophilic spacer chain, -(Sar-Sar-Pro)2-, was placed between Tyr-D-Ala-Gly-Trp-Leu (an enkephalin part) and a phospholipid part to diminish steric hindrance of the liposome against receptor binding of the enkephalin unit. The affinity of the immobilized enkephalin conjugate for opioid receptor was dependent on the density of the enkephalin unit on the surface of polymerized liposome, indicating that more than two enkephalin units on a liposome simultaneously bind to receptors in the membrane. IC50 values for the delta- and mu-receptors were 15 and 26 nM, respectively, when the conjugate was immobilized at the molar ratio of [enkephalin]/[phospholipid] of 340. The latter affinity is better than that of Tyr-D-Ala-Gly-Trp-Leu (50 nM). The enkephalin part was located at the membrane surface, as indicated by fluorescence spectroscopy. When 12% cerebroside sulfate was mixed in the polymerized liposome, delta-receptor affinity of the immobilized enkephalin conjugate was improved to 7.4 nM. The environment around the enkephalin part became hydrophilic upon incorporation of cerebroside sulfate into the polymerized liposome, resulting in changes in the receptor affinities.

Lipid membrane permeability of modified c[D-Pen2, D-Pen5]enkephalin peptides

Permeability coefficients of a series of analogues of a potent opioid peptide, c[D-Pen2, D-Pen5]enkephalin, were measured in a model membrane system. The analogues included hydrophobic amino acid substitutions on position 3. Liposomes of a mixed composition consisting of zwitterionic lipids and cholesterol served as the model membranes. The obtained permeability coefficients range between 0.38 x 10(-12) and 2.9 x 10(-12) cm/s. These data were correlated with the hydrophobicity scale of Nozaki and Tanford (J. Biol. Chem. 246, 1971, 2211-2217) (correlation coefficient = 0.9933) and with determinations of lipid order perturbation by differential scanning calorimetry (correlation coefficient = -0.9779). The reasonably good correlation obtained within the family of analogues substituted on position 3 (Gly, Ala, Leu, Phe) indicates that changes in permeabilities are primarily related to increases in the partition coefficient of the peptide. However, Phe residue added on the N-terminal end of the peptide (position 0) does not appear to follow the observed trend, showing stronger lipid perturbation and lower permeability compared to the Phe3 analog. This observation demonstrates that each class of peptide modifications requires a new basis of permeability analysis and predictions.

Purification, sequence analysis, and cellular localization of a prodynorphin-derived peptide related to the alpha-neo-endorphin in the rhynchobdellid leech Theromyzon tessulatum

Cells immunoreactive to an antiserum specifically directed against vertebrate alpha-Neo-endorphin (alpha-NE) were detected in the internal wall of anterior and posterior suckers of the rhynchobdellid leech Theromyzon tessulatum. These cells have morphological and ultrastructural characteristics close to the "releasing gland cells" of adhesive organs. The epitope recognized by anti-alpha-NE was contained in granules having a diameter of 0.2-0.3 microm. Previous works involving the brain of this leech demonstrate the existence of approximately 14 neurons immunoreactive to the anti-alpha-NE. Following an extensive purification including high pressure gel permeation and reversed-phase high performance liquid chromatography, epitopes contained in both suckers and central nervous system were isolated. Purity of the isolated peptides was controlled by capillary electrophoresis. Their sequences were determined by a combination of automated Edman degradation, electrospray mass spectrometry measurement, and coelution experiments in reversed-phase high performance liquid chromatography with synthetic alpha-NE. The results demonstrate that epitopes recognized by the anti-alpha-NE in the suckers and the central nervous system are identical to vertebrate alpha-NE (YGGFLRKYPK). This finding constitutes the first biochemical characterization of a prodynorphin-derived peptide in invertebrates. Moreover the isolation of this peptide in the annelida establishes the very ancient phylogenetic origin of alpha-NE as well as its conservation in evolution.

Separation of biologically active peptides by capillary electrophoresis and high-performance liquid chromatography

HPLC and CE have been applied to the separation of some newly synthesized substances, including nonapeptides from the intrachinary region of insulin, insulin-like growth factors I and II (IGF I and II) and some penta- and hexapeptides. All the peptides are satisfactorily separated using a reversed-phase HPLC system with a C18 stationary phase and mobile phases of 20-40% acetonitrile (v/v) and 0.2% trifluoroacetic acid in water (v/v). The best CE separation of IGF I and II has been achieved in a 30 mM phosphate buffer (pH 4-5), whereas 150 mM phosphoric acid (pH 1.8) is optimal for the insulin nonapeptides. The latter electrolyte is also suitable for the CE separation of the hexapeptides, as is a micellar system containing 20 mM borate-50 mM sodium dodecyl sulfate (pH 9.0). Complete CE resolution of the D- and L-forms is possible in a 50 mM phosphate buffer (pH 2.5) containing 10 mM beta-cyclodextrin. UV spectrophotometric detection was used throughout, at wavelengths from 190 to 215 nm. The CE procedures are, in general, preferable to HPLC separations, as they exhibit better separation efficiencies, are faster and consume smaller amounts of analytes and reagents.

The PC12 rat pheochromocytoma cell line expresses the prodynorphin gene and secretes the 8 kDa dynorphin product

Most adrenal chromaffin cells synthesize opioids derived from proenkephalin but not from prodynorphin. However, human pheochromocytomas and the PC12 rat pheochromocytoma cell line synthesize dynorphins. The aim of this study was to confirm the presence of the authentic prodynorphin transcript and its dynorphin product in PC12 cells. We have found that the sequence of a 458 bp cDNA fragment derived from RT-PCR amplification of total PC12 RNA was in complete accordance with the published sequence of the equivalent region of the prodynorphin gene. It encodes the potent endogenous kappa opioid agonists alpha-neo-endorphin, dynorphin A and dynorphin B. Furthermore, immunoaffinity-purified PC12 cell extracts were subjected to RP-HPLC. Most of its IR-dynorphin eluted on a peak exhibiting the retention time of similarly treated rat anterior pituitary. The expression of the prodynorphin gene in pheochromocytomas can be explained as either the result of (a) the process of dedifferentiation of chromaffin cells to pheochromocytoma which may thus cause the expression of a previously unexpressed prodynorphin or that (b) those pheochromocytomas expressing the prodynorphin gene derive from the few, centrally located chromaffin cells, which express this gene even under normal conditions.

Phosphorylation of enkephalins enhances their proteolytic stability

Pharmacological action of enkephalins as opioid peptides is limited because of their rapid degradation by endoproteases. A novel approach is used in this study to prolong the life of those peptides. Phosphorylation of N-terminal tyrosine residue is found to have a profound influence in improving the stability of [Met]enkephalin and [Leu]enkephalin against the action of aminopeptidase M. Whereas, breakdown of [Met]enkephalin and [Leu]enkephalin is essentially complete in less than one min when incubated at 37 degree C with purified aminopeptidase M (EC3.4.11.2; substrate:enzyme = 1:0.1) in Tris buffer (pH 7.02), the corresponding phospho analogs are still detected 60 min after start of incubation. The rate of disappearance of phospho-[Met]enkephalin and phospho-[Leu]enkephalin follows first-order kinetics with half-lives of 7.3 and 8.3 min, respectively.

Development of a model for the delta-opioid receptor pharmacophore: 3. Comparison of the cyclic tetrapeptide, Tyr-c[D-Cys-Phe-D-Pen]OH with other conformationally constrained delta-receptor selective ligands

We have previously proposed a model of the delta-opioid receptor bound conformation for the cyclic tetrapeptide, Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13) based on its conformational analysis and from conformation-affinity relationships observed for its analogues with modified first and third residues. To further verify the model, it is compared here with results of conformational and structure-activity studies for other known conformationally constrained delta-selective ligands: the cyclic pentapeptide agonist, Tyr-c[D-Pen-Gly-Phe-D-Phe]OH (DPDPE): the peptide antagonist, Tyr-Tic-Phe-PheOH (TIPP); the alkaloid agonist, 7-spiroindanyloxymorphone (SIOM); and the related alkaloid antagonist, oxymorphindole (OMI). A candidate delta-bound conformer is identified for DPDPE that provides spatial overlap of the functionally important N-terminal NH3+ and C-terminal COO- groups and the aromatic rings of the Tyr and Phe residues in both cyclic peptides. It is shown that all delta-selective ligands considered have similar arrangements of their pharmacophoric elements, i.e., the tyramine moiety and a second aromatic ring (i.e., the rings of Phe3, Phe4, and Tic2 residues in JOM-13, DPDPE, and TIPP, respectively; the indole ring system in OMI, and the indanyl ring system in SIOM). The second aromatic rings, while occupying similar regions of space throughout the analogues considered, have different orientations in agonists and antagonists, but identical orientations in peptide and alkaloid ligands with the same agonistic or antagonistic properties. These results agree with the previously proposed binding model for JOM-13, are consistent with the view that delta-opioid agonists and antagonists share the same binding site, and support the hypothesis of a similar mode of binding for opioid peptides and alkaloids.

Cat proenkephalin-A does not contain the opioid octapeptide

The sequence of a large cDNA fragment of proenkephalin-A from the cat adrenal medulla was obtained using reverse transcription followed by polymerase chain reaction, and cloning. This cDNA encompasses the region normally containing all the opioid peptides, except the C-terminal heptapeptide. As with other species, cat proenkephalin-A contains four conserved copies of (Met5)-enkephalin, and one of (Leu5)-enkephalin, flanked by processing sites of paired basic amino acids. However, significant differences were found in the nucleotide and deduced amino acid sequences in the region of the octapeptide. In particular, the essential tyrosyl residue is substituted by a histidyl residue, making it unlikely that the cat equivalent would have opioid activity. Furthermore, the peptide is not flanked by paired basic residues, suggesting it is not processed.

The C-terminal bisphosphorylated proenkephalin-A-(209-237)-peptide from adrenal medullary chromaffin granules possesses antibacterial activity

The chromaffin granules have been shown to be an excellent model to study the processing of proenkephalin-A and chromogranins. Recently, we reported a study dealing with the processing of chromogranin B/secretogranin I and the occurrence of the C-terminal chromogranin B-derived peptide 614-626 which was shown to have antibacterial activity [Strub, J.M., Garcia-Sablone, P., Looning, K., Taupenot, L., Hubert, P., Van Dorsselaer, A., Aunis, D. & Metz-Boutigue, M.H. (1995) Eur. J. Biochem. 229, 356-368]. We also observed that this new antibacterial activity present in chromaffin granules was associated with other endogenous protein-derived fragments yet to be characterized. The present study reports the isolation and characterization of a peptide which possesses antibacterial activity and which corresponds to the C-terminal 209-237 sequence of proenkephalin-A. A detailed study using microsequencing and matrix-assisted-laser-desorption time-of-flight mass spectrometry (MALD-TOF MS) allowed us to correlate the antibacterial activity of this peptide named enkelytin (FAEPLPSEEEGESYSKEVPEMEKRYGGFM) with post-translational modifications. Endogenous bisphosphorylated proenkephalin-A-(209-237) was active on Micrococcus luteus and Bacillus megaterium killing bacteria in the 0.2 - 0.4 microM range but was inactive in similar conditions towards Escherichia coli. Enkelytin shares sequence and structural similarities with the antibacterial C-terminal domain of diazepam-binding inhibitor. According to this similarity, a prediction of secondary structure is proposed for enkelytin and discussed in relationship to its biological activity.

A comparative study of immunomodulation produced by in vitro exposure to delta opioid receptor agonist peptides

The present study assessed the direct immunomodulatory effect of a panel of synthetic peptides exhibiting delta-opioid receptor agonist activity. Murine splenic lymphocytes and peritoneal macrophages were cultured in vitro with peptides at concentrations of 0.00001-10 microM. Assessment was made of B-cell function by quantitating cellular proliferation, T-cell function by measuring cytokine production, natural immunity by quantitating basal and cytokine-augmented natural killer (NK) cell activity, and macrophage function by production of IL-6. These peptides had minimal effects on B-cell proliferation at any concentration examined. In comparison, enhancement of cytokine production by T-helper cells occurred following exposure to several of the compounds, to a significant extent with DPDPE, DPDPE-trifluoroacetate, or deltorphin-1 and most pronounced at concentrations between 0.00001 and 0.1 microM. Likewise, IL-6 production by macrophages was significantly augmented by exposure to these three peptides. NK cell function was significantly enhanced by in vitro exposure to several of the peptides, with enhancement generally noted at concentrations between 0.00001 and 0.01 microM. However, some of the peptides (most notably DADLE) greatly suppressed NK cell activity. These data suggest that delta opioid agonists are broadly immunomostimulatory.

Conformational restriction of Tyr and Phe side chains in opioid peptides: information about preferred and bioactive side-chain topology

The side chain of Tyr and Phe was fixed into the gauche(-) or gauche(+) conformation by using the Tic Htc structures, and into the trans conformation by using an aminobenzazepine-type (Aba) structure. When incorporated into dermorphin or deltorphin II, the Tic and Htc analogues all showed a large decrease in both mu and delta affinities and activities. Fixation of Phe(3) in the trans rotamer resulted in a large increase in delta affinity in the dermorphin analogue, whereas in the [Aba(3)-Gly(4)] deltorphin II analogue, good delta affinity is maintained despite the removal of the Glu side chain. Whereas several authors propose a gauche(-) preferred conformation for the Phe(3) side chain, these results suggest a trans conformation at the delta receptor. The use of these conformationally constrained residues for evaluating the preferred solution conformation in the flexible N-terminal tripeptide Tyr-D-Ala-Phe is illustrated. The (1)H-nmr parameters--chemical shift, temperature dependence, and nuclear Overhauser effects to the D-Ala(2) methyl protons in the different analogues--provide direct evidence to confirm the proposed sandwich conformation in the native peptides.

Chemiluminescent nitrogen detection as a new technique for purity assessment of synthetic peptides separated by reversed-phase HPLC

Reversed phase high-performance liquid chromatography with chemiluminescent nitrogen detection (HPLC-CLND) was used for the quantitative analysis of peptides manufactured by solid-phase peptide synthesis. CLND provided quantitative information regarding the nitrogen distribution of peptide samples following HPLC separation. This technique permits the universal quantitation of the "peptide content" of synthetic peptides in an on-line mode without pre- or post-column derivatization and free of interference from non-nitrogen-containing UV chromophores. This paper will show the utility of this novel technique in measuring the peptide content of crude synthetic proinsulin chain C peptide. A mixture of five reference peptides was analyzed to show the homogeneity of the CLND response and used to determine peptide content. Application for the purified product is also discussed. The detection profiles were acquired in parallel with a UV detector.

Mass spectrometry, high performance liquid chromatography, and brain peptides

This paper is a personal recollection of some of the events and research that surrounded the amino acid sequence determination of the hypothalamic releasing factor, TRF (now known as TRH), by mass spectrometry (MS), and the development of reverse phase high performance liquid chromatography (RP-HPLC) MS and tandem MS (MS/MS) methods for the qualitative and quantitative analysis of native opioid neuropeptides in human pituitary tissue extracts.

Quadrupole ion trap mass spectrometry

A number of other features of ITMS systems that will enhance their ability to analyze biological macromolecules are worth mentioning. As has already been demonstrated for ESI/quadrupole, ESI/magnetic sector, and ESI/FTICR systems, the capability of inducing fragmentation of the ESI-generated multiply charged ions of biological macromolecules in the capillary/skimmer region of the ESI source and subsequently selectively analyzing fragments can also be carried out with the QITMS, as we have demonstrated using bovine serum albumin (data not shown). The ability to carry out chemical reactions on biological macromolecules inside the QITMS has been demonstrated by McCluckey et al. by showing that the introduction of a pulse of volatile base, such as diethylamine, can result in proton removal from multiply charged protein ions, resulting in species with lower charge states. The application of the technique of deuterium exchange of active hydrogens on peptides to simplify the interpretation of MS/MS sequencing experiments can be implemented for ESI/QITMS. Carrying out such exchange inside the ITMS may also be possible, with resulting analytical advantages. Reports of a hybrid QITMS-TOF system, which was operated with either ESI or MALDI methodology, and which demonstrated low femtomolar sensitivity with higher resolution of the TOF analyzer because of ion injection of essentially monoenergetic ions from the QITMS into the TOF, illustrate additional uses of the QITMS. The reverse combination (e.g., ESI/TOF/QITMS or MALDI/TOF/QITMS) could afford preselection of ions for even higher performance in the QITMS, because space charging (loss of performance such as resolution because of too much charge in close proximity in the ion trap) would be minimized. Opportunities for the application of QITMS technology for the analysis of biological macromolecules abound, including ultrahigh-sensitivity protein sequencing using specifically derivatized amino acids released by Edman chemistry; rapid sequencing of MHC-associated antigenic peptides of variable length (approximately nonamers for the MHC I complexes to > dodecamers for the MHC II complexes), which are available in only very low amounts (femtomole/attomole) and in very complex mixtures (5000-10,000 species) of closely related peptide structures; ultrahigh-sensitivity analysis of peptides and proteins directly in vivo using microelectrospray; direct analysis of metal ion binding to peptides and proteins and analysis of noncovalent interactions, including conformation; and possible analysis of plasmid DNA, as has been suggested by ESI ionization of a 2-MDa DNA species. In summary, the ability of the QITMS to interface to key separations systems such as HPLC and HPCE through the critical ionization techniques of ESI and MALDI, coupled with the high mass range, high mass resolution, high sensitivity, high-efficiency CID, and MS capabilities of this device, will provide an astonishing array of cost-effective capabilities for the qualitative and quantitative analysis of biological macromolecules.

A proenkephalin A-derived peptide analogous to bovine adrenal peptide E from frog brain: purification, synthesis, and behavioral effects

A peptide derived from the posttranslational processing of proenkephalin A was isolated from an extract of the brain of the European green frog Rana ridibunda and its primary structure established as: Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-Gly-Arg10- Pro-Glu-Trp-Trp-Gln-Asp-Tyr-Gln-Lys-Arg20-Tyr-Gly-Gly-Phe-Met. The structure was confirmed by chemical synthesis. The peptide represents an amphibian equivalent of bovine adrenal peptide E [preproenkephalin A (206-230)-peptide] but the sequence contains two amino acid substitutions (Met15-->Gln and Leu25-->Met) compared with the mammalian peptide. The data support previous hypotheses that the Leu-enkephalin sequence is not present in preproenkephalin A of amphibians. Intracerebroventricular injections of frog peptide E (10 and 100 ng) in mice had no significant effect on horizontal locomotor activity. The peptide, in doses up to 1 microgram, had no effect on latency of escape jumping in the hot plate test and the peptide (100 ng) did not modify responses (paw licking, rearing, and escape jumping) in morphine-treated mice.

B-lymphoma cells are activated by peptide ligands of the antigen binding receptor or by anti-idiotypic antibody to induce extracellular acidification

Synthetic peptide ligands specific for the surface immunoglobulin receptor of the human Burkitt's lymphoma cell line SUP-B8, previously identified using phage display libraries, induced apoptosis of the SUP-B8 cells in vitro when administered as dimers or tetramers. The use of synthetic peptide ligands is being explored for immunotherapy of B-cell lymphoma. It will be critical to identify which of the peptide ligands identified are the most active functionally. Using the Cytosensor microphysiometer, SUP-B8 cells and B-lymphoma cells obtained from patients were found to acidify their extracellular environment within minutes of specific activation by surrogate peptide ligands or by anti-idiotype antibodies. This signal was blocked by pretreatment of the lymphoma cells with the tyrosine kinase inhibitor genistein. Treatment of SUP-B8 cells with dimeric and tetrameric specific peptide ligands caused a rapid increase in extracellular acidification rate, which peaked after 10 min at approximately 15 and 20% above basal rates, respectively. These responses were blocked by excess monomeric peptide. To evaluate the ability of different peptide ligands to induce a signal directly on lymphoma cells, thereby establishing their relative affinity to the surface immunoglobulin receptor, acidification rate changes were measured at varying peptide concentrations. The microphysiometer signal correlated with the known relative affinities and antiproliferative potencies of the peptides. This approach is particularly useful for primary tumor cells that cannot be cultured. The signal may be predictive of the efficacy of treatment with synthetic peptide ligands and may be useful in the evaluation of ligands for other cell surface receptors with biological effects on B-lymphoma cells.

The in vitro and in vivo resistance of synthetic enkephalin analogs to three enkephalin-hydrolyzing enzymes

The magnitude of the in vitro and in vivo resistance of 3 synthetic enkephalin analogs, [D-Ala2,Met5]-enkephalin (DAME), [D-Ala2,Met5]-enkephalinamide (DAME-NH2) and [D-Ala2,D-Met5]enkephalin (DADME), to 3 enkephalin-hydrolyzing enzymes, amastatin-sensitive aminopeptidase (AsA), phosphoramidon-sensitive endopeptidase-24.11 (PsE) and captopril-sensitive dipeptidyl carboxypeptidase I (CsD), was estimated by comparing the potency of enkephalins in the absence of the peptidase inhibitor (PI) with that in the presence of the PI. The enhancement of the potency of enkephalins in the isolated mouse vas deferens preparation by 3 PIs, amastatin, phosphoramidon, and captopril, indicated that the resistance of enkephalins to AsA, PsE, or CsD was DADME [symbol: see text] DAME-NH2 [symbol: see text] DAME > [Met5]-enkephalin (ME), DADME > DAME-NH2 > DAME [symbol: see text] ME, or DADME [symbol: see text] DAME-NH2 > DAME > ME, respectively. Additionally, the data obtained by the s.c. administration of enkephalin analogs to 10-day-old rats with or without PI, showed that PsE played the most important role in the inactivation of both DAME and DAME-NH2. In addition to PsE, both AsA and CsD, or AsA alone, played the significant role in the inactivation of DAME, or DAME-NH2, respectively. In the inactivation of DADME, AsA alone played the significant role. These results showed that the 3 peptidases all played important roles in the inactivation of enkephalins, and therefore only an analog like DADME, which was quite resistant to the 3 enzymes, was able to produce the effect without PIs after its systemic administration. Since even DADME was not completely resistant to the 3 enzymes; however, its potency was further increased by pretreatment of infant rats with the PIs.

Synthesis and bioactivity studies of 1-adamantanamine derivatives of peptides

Small enkephalin-related peptides containing a 1-adamantanamine moiety coupled through an amide linkage at the C-terminus were synthesized. Several of the compounds showed high mu opioid activity and mu receptor selectivity. The new adamantanamine derivatives were also examined for antiviral activity against HIV-1 in a cell culture system. Some of them inhibited syncytia formation even when the antigen assay gave evidence for viral replication.

Antibodies against the amino-terminal portion of pro-enkephalin inhibit DNA synthesis in human peripheral mononuclear cells

Pro-enkephalin (PENK) mRNA and PENK-derived peptides have been reported in lymphocytes, monocytes, and macrophages. Met-enkephalin (ME) and/or synenkephalin (SYN)-containing peptides are produced and released by human peripheral blood lymphocytes (HPBL) activated with phytohemagglutinin (PHA). Furthermore, SYN (PENK 1-70) was cleaved to low-molecular-mass peptides in HPBL. In this work we studied the effect of a mouse monoclonal antibody (mAb) and a rabbit antiserum (pAb) against the C-terminal portion of SYN on DNA synthesis in PHA-activated HPBL. [3H]Thymidine incorporation into HPBL incubated with 0.1 microgram/ml of PHA was tested in the presence of different concentrations of mAb immunoglobulin (Ig) G or different dilutions of pAb. mAb induced a concentration-dependent decrease of [3H]thymidine incorporation into HPBL: 7%, 19%, 28%, and 35% of inhibition was observed with 0.1, 1, 1.5, and 2 micrograms IgG, respectively, reaching values of 65% with 10 micrograms IgG. Similarly, pAb dilutions of 1/500, 1/1000, 1/2000 and 1/4000 inhibited DNA synthesis by 63%, 61%, 43%, and 30%, respectively. The inhibitory effect of mAb and pAb was specific since it was not produced by non-immune mouse IgG or several non-immune rabbit sera and was completely reversed by 1 microM of the synthetic peptide [Tyr63](syn 63-70) synenkephalin. These results suggest that low-molecular-mass SYN-derived peptides released by PHA-activated HPBL may participate in the proliferative response of these cells. This is further evidence that the non-opioid portion of PENK--that is, SYN-derived peptides--may be involved in tissue development.

"Prohormone thiol protease" (PTP) processing of recombinant proenkephalin

The "prohormone thiol protease" (PTP) from adrenal medullary chromaffin granules has been demonstrated as a novel cysteine protease that converts the model enkephalin precursor, ([35S]Met)-preproenkephalin, to appropriate enkephalin related peptide products [Krieger, T. J., & Hook, V. Y. H. (1991) J. Biol. Chem. 266, 8376-8383; Kreiger, T. J., Mende-Mueller, L., & Hook, V. Y. H. (1992) J. Neurochem. 59, 26-31; Azaryan, A. V., & Hook, V. Y. H. (1994) FEBS Lett. 341, 197-202]. In this report, PTP processing of authentic proenkephalin (PE) was examined with respect to production of appropriate intermediate products, and kinetics of PE processing were assessed. Recombinant PE was obtained by high level expression in Escherichia coli, with the pET3c expression vector; PE was then purified from E. coli by DEAE-Sepharose chromatography, preparative gel electrophoresis, and reverse-phase HPLC. Authentic purified PE was confirmed by amino acid composition analyses and peptide microsequencing. In time course studies, PTP converted PE (12 microM) to intermediates of 22.5, 21.7, 12.5, and 11.0 kDa that represented NH2-terminal fragments of PE, as assessed by peptide microsequencing. Differences in molecular masses of the 22.5, 21.7, 12.5, and 11.0 kDa products reflect PTP processing of PE within the COOH-terminal region of PE, which resembles PE processing in vivo [Liston, D. L., Patey, G., Rossier, J., Verbanck, P., & Vanderhaeghen, J. (1983) Science 225, 734-737; Udenfriend, S., & Kilpatrick, D. L. (1983) Arch. Biochem. Biophys. 221, 309-314]. Products of 12.5, 11.0, and 8.5 kDa were generated by PTP cleavage between Lys-Arg at the COOH-terminus of (Met)enkephalin-Arg6-Gly7-Leu8.(ABSTRACT TRUNCATED AT 250 WORDS)

Capillary electroseparations of enkephalin-related peptides and protein kinase A peptide substrates

The separations of enkephalin-related peptides and protein kinase A peptide substrates, with the common structural feature -Arg-Arg-X-Ser-Val-, were studied in micellar electrokinetic chromatography (MEKC) systems and compared with the capillary zone electrophoresis (CZE) mode. The influence of the magnitude and the direction of the electroosmotic flow on the selectivity was studied. Reversed electroosmosis was obtained by adding a hydrophobic amine, dimethyldodecylamine, to the background electrolyte; the amine forms cationic micelles with a low critical micelle concentration (0.3 mM). The neutral micellar agent, Brij 35, competes with the amine for adsorption sites on the capillary surface decreasing the reversed electroosmosis. In such a system, mixed cationic micelles are formed to which the peptides were not distributed at low pH, but an improved resolution was obtained due to the effects on electroosmosis. In systems containing the less hydrophobic amine dimethyloctylamine, in which probably no mixed micelles are formed, an improved separation of protein kinase A peptide substrates was obtained due to distribution to Brij 35 micelles. In separations of enkephalins, a high pH gave very low efficiencies due to surface-analyte interactions, and the best CZE separations were obtained at low pH. Changes in migration order were observed in the pH range 2-3, possibly due to differences in peptide pKa values or conformation changes of the peptides. The enkephalins were only to a small extent distributed to the Brij 35 micelles, but this improved the separation at pH 2 compared to the CZE mode.

Performance of amino-silylated fused-silica capillaries for the separation of enkephalin-related peptides by capillary zone electrophoresis and micellar electrokinetic chromatography

Enkephalin-related peptides were separated at low pH in a capillary with covalently bonded aminopropyl groups. The peptides are electrostatically repelled from the capillary surface and much higher efficiencies and faster separations were achieved compared to separations using uncoated capillaries. At low pH the amino groups are protonated, which results in reversed electroosmosis. The influence of voltage and ionic strength on the mobility and the separation efficiency was studied. The repeatability of migration times within one day was very good with relative standard deviations of 0.3-0.7%. Increasing the pH decreased the electroosmosis, eventually turning towards the cathode in the pH range 5-6; the separation performance, however, was lower at higher pH. Neutral and anionic micellar agents were added to the background electrolyte at different concentrations; the enkephalins had weak association with the neutral micellar agents but were distributed to the anionic taurodeoxycholic acid (TDC) micelles, giving rise to changes in separation selectivities. Very high efficiencies were obtained for peptides with a low distribution to the TDC micelles, while the efficiencies were impaired for those with a strong association with the micelles, which may indicate a slow mass transfer in the association process.

Mouse insulinoma beta TC3 cells express prodynorphin messenger ribonucleic acid and derived peptides: a unique cellular model for the study of prodynorphin biosynthesis and processing

The tumor cell line beta TC3 has been established from insulinomas derived from transgenic mice carrying a hybrid insulin promoter-simian virus-40 tumor antigen gene. The beta TC3 cells express high steady state levels of proinsulin messenger RNA (mRNA). In this same cell line, we describe in the present study high expression levels of prodynorphin (pro-Dyn) mRNA and its derived peptides. By Northern blot analysis, the screening of 23 cell lines of endocrine (n = 10) and of nonendocrine (n = 13) origin revealed the presence of high levels of the 2.6-kilobase pro-Dyn transcript only in beta TC3 cells. The beta TC3 cells expressed levels of pro-Dyn mRNA comparable to those in rat tissues expressing pro-Dyn. Chromatographic and radioimmunological studies showed that pro-Dyn mRNA was translated and fully processed into opioid peptides with leucine-enkephalin (Leu-Enk)-extended sequences [dynorphin-A-(1-8), dynorphin-B-(1-13), and alpha-neo-endorphin]. The expression of the prohormone convertases was also examined in beta TC3 cells by Northern blot analysis. In addition to the ubiquitously expressed furin, beta TC3 cells have abundant levels of prohormone convertase-1 (PC1) and PC2 mRNAs, but undetectable levels of PACE4 or PC5 mRNAs. Incubation of beta TC3 cells with 8-bromo-cAMP for 24 h stimulated 3-fold both the pro-Dyn mRNA levels and the secretion of opioid peptides. In contrast to pro-Dyn mRNA, furin, PC1, and PC2 mRNA levels were not affected by 8-bromo-cAMP. The beta TC3 cells constitute a unique model to elucidate the biosynthetic pathway of pro-Dyn processing, to identify the proteolytic enzymes responsible for the production of pro-Dyn end products, and to assess the potential role of opioid peptides in the regulation of pancreatic function.

The three-dimensional solution structure of a constrained peptidomimetic in water and in chloroform. Observation of solvent induced hydrophobic cluster

A large number of protein-protein interactions involved turn or loop regions. The excised linear peptides from these regions reveal complex conformational averaging. To circumvent this motional averaging and to stabilize the beta-turn conformation, extensive effort has been devoted to the design of constrained peptidomimetics. Here, we report the three-dimensional solution structure of a 12-membered cyclic peptidomimetic. The structures were calculated from NMR studies performed in chloroform and in water at 263 and 278K, respectively. This 12-membered cyclic scaffolding is part of a program to design and to construct conformationally stable beta-turn peptidomimetics. The impact of the surrounding environment on the conformation of this constrained peptidomimetic is discussed. The general structural features of the cyclic mimetic are retained in both environments; however, the formation of a hydrophobic patch in the aqueous solvent is evident.

Isolation and structural characterization of enkephalins in the brain of the rhynchobdellid leech Theromyzon tessulatum

This paper reports the purification of four peptides related to enkephalins from the brain of the leech Theromyzon tessulatum. After reverse-phase HPLC purification, the sequence of the enkephalins (YGGFM, YGGFL, FM, FL) was established by a combination of automated Edman degradation, electrospray mass spectrometry measurement, and co-elution experiments in reverse-phase HPLC with synthetic peptides. ELISA titrations performed on each purified peptide indicated that the major amount was borne by the leucine-enkephalin. The ratio of leucine-enkephalin and methionine-enkephalin of 2:1 is in line with previous immunocytochemical data obtained on T. tessulatum brains. The presence of enkephalins in T. tessulatum, an animal belonging to the oldest group of coelomate metazoans (the Annelida) establishes the very ancient phylogenetic origin of opioids and their conservation in the course of evolution.

Thermal decomposition kinetics of protonated peptides and peptide dimers, and comparison with surface-induced dissociation

Rate constants for the unimolecular decomposition of peptide monomer and dimer ions by thermal and surface-induced dissociation (SID) are measured and compared. Rate constants for thermal dissociation are measured in a heated wide-bore capillary flow reactor attached in front of the capillary leading into the mass spectrometer. Thermal decomposition of the leucine enkephalin ion (YGGFL)H+ is observed between 600 and 680 K with rate constants of 20-200 s-1, and yields many of the same fragments as SID at 35 eV, although with different relative intensities. The thermal decomposition yields the Arrhenius parameters Ea = 38.3 kcal/mol, log A = 15.7. The decomposition of the monomer and dimer ions are also observed by using SID on C18 and fluorinated hydrocarbon surfaces, with rate constants of 2 x 10(4) to 40 x 10(4) s-1. The SID activated monomer ions are assigned equivalent temperatures of 710-840 K by extrapolation of the thermal activation parameters. The protonated dimer ion (YGGFL)2 H+ decomposes thermally at 500-540 K to yield the monomer ion. The dimer also decomposes by SID at low collision energies 10-20 eV on both surfaces to yield the monomer ion, and at much higher energies of 60-80 eV to yield fragments identical to the decomposition of the monomer. The large energy requirement for fragmentation from the dimer is due to energy deposition into more degrees of freedom plus the additional energy required for dissociation of the dimer to the monomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Nasal mucosal metabolism and absorption of pentapeptide enkephalin analogs having varying N-terminal amino acids

A series of enkephalin analogs with varying amino acids on the N-terminus were synthesized and evaluated in rats in situ for their hydrolytic stability and absorption when administered nasally. The amino acids on the N-terminus were tyrosine (Y), alanine (A), serine (S), lysine (K), and aspartic acid (D). These amino acids represent different charges and sizes. Among these peptides, only the peptide carrying aspartic acid on the N-terminus was stable. The rank order of degradation rates was YGGFL > AGGFL > SGGFL, KGGFL > DGGFL. These results suggest that there are relatively high activities of aminopeptidases N and B and relatively low activity of aminopeptidase A in the rat nasal mucosa. Absorption studies were performed to determine the absorption rate of DGGFL, by measuring percentage recovery of nasal doses vs time. After a 50 microL dose of a 3 mg/mL solution, this peptide exhibited an absorption half-life of 21 min, which is similar to the nasal absorption rate of YGGFL.

In search of the 'bio-active conformation'--is it induced by the target cell membrane?

Conformations of regulatory peptides interacting with artificial lipid membranes were compared with those of chemically constrained molecules that react selectively with different receptor classes. Striking similarities in the topochemistry of molecules with similar activity were observed. The membrane-induced topomers were almost congruent with the artificial topomers that are selectively recognized by the same receptors. Finally, the ideas developed in the membrane compartments theory which allow a quantitative prediction of receptor preference are compatible with our present knowledge of receptor structure.

Amino acid sequence determination of phosphoenkephalins using liquid secondary ionization mass spectrometry

Liquid secondary ionization mass spectrometry (LSIMS) operating in the positive- and negative-ion modes was used to study fragmentation profiles and to obtain the amino acid sequences of a set of seven phosphoenkephalin peptides. The use of glycerol as the liquid matrix led to increase in fragmentation of phosphopeptides. The prominent amino acid sequence-determining ions in the positive-ion mode are y-type C-terminal ions; the N-terminal sequence-specific ions are observed sporadically. The most dominant ions in those mass spectra, however, are the immonium ions and a few low-mass side-chain cleavage products. The mass spectra in the negative-ion mode are more information-rich, and provide data complementary to that from the positive-ion mode. The phosphate group marker ions, m/z 79 (PO-3) and 97 (H2PO-4), are prominent and both N- and C-termini sequence ions are formed with equal facility in this mode of analysis. Both positive- and negative-ion mass spectral data are useful in determining the amino acid sequence of all the seven phosphoenkephalins. Thus, LSIMS alone can be a viable option to the tandem mass spectrometry approach when sufficient quantities (> 50 nmol) of phosphopeptides are available.

Opioid peptide receptor studies. 3. Interaction of opioid peptides and other drugs with four subtypes of the kappa 2 receptor in guinea pig brain

Using guinea pig, rat, and human brain membranes depleted of mu and delta receptors by pretreatment with the site-directed acylating agents BIT (mu selective) and FIT (delta selective), previous studies from our laboratory resolved two subtypes of the kappa 2 binding site, termed kappa 2a and kappa 2b. In more recent studies, we used 6 beta-[125Iodo]-3,14-dihydroxy-17-cyclopropylmethyl-4,5 alpha-epoxymorphinan ([125I]IOXY) to characterize multiple kappa 2 binding sites in rat brain. The results indicated that [125I]IOXY, like [3H]bremazocine, selectively labels kappa 2 binding sites in rat brain membranes pretreated with BIT and FIT. In the rat brain, using 100 nM [D-Ala2-MePhe4,Gly-ol5]enkephalin to block [125I]IOXY binding to the kappa 2b site, we resolved two subtypes of the kappa 2a binding site. In the present study we examined the binding of [125I]IOXY to the kappa 2 receptors of guinea pig brain. As observed in rat brain, [125I]IOXY, under appropriate assay conditions, selectively labels kappa 2 binding sites. Quantitative binding studies readily demonstrated the presence of kappa 2a and kappa 2b binding sites. The kappa 2a binding sites were selectively assayed using 5 microM [Leu5]enkephalin to block [125I]IOXY binding to the kappa 2b sites, and kappa 2b sites were selectively assayed using 5 microM (-)-(1S,2S)-U50,488 to block [125I]IOXY binding to the kappa 2a sites. Under these conditions, two subtypes of the kappa 2a site were resolved with high (kappa 2a-1) and low (kappa 2a-2) affinity for nor-BNI (Ki values = 0.88 and 476 nM) and CI977 (Ki values = 17.5 and 95,098 nM). Similarly, two subtypes of the kappa 2b site were observed with high (kappa 2b-1) and low (kappa 2b-2) affinity for [D-Ala2-MePhe4,Gly-ol5]enkephalin (DAMGO) (Ki values = 97 and 12,321 nM) and alpha-neoendorphin (Ki values = 33 and 5308 nM). Two-site models were also resolved in the presence of 100 microM 5'-guanylyimidodiphosphate (GppNHp). We carried out detailed ligand selectivity analysis of the multiple kappa 2 binding sites. Most test agents were either nonselective or selective for the kappa 2a-1 site. Nalbuphine was moderately selective for the kappa 2a-2 site. Similarly, although most test agents were either nonselective or selective for the kappa 2b-1 site, butorphanol, and the delta antagonists naltrindole, naltriben, and 7-benzylidene-7-dehydronaltrexone were moderately selective for the kappa 2b-2 site.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of a model for the delta opioid receptor pharmacophore. 2. Conformationally restricted Phe3 replacements in the cyclic delta receptor selective tetrapeptide Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13)

The in vitro pharmacological properties and conformational features of analogs of the delta opioid receptor selective tetrapeptide Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13) in which the Phe3 residue was replaced by each of the four stereoisomers of beta-methylphenylalanine (beta-MePhe) were investigated. Both analogs in which the alpha carbon of the Phe3 replacement has L-stereochemistry display high affinity for delta receptors with the (2S,3S)-MePhe3 analog exhibiting approximately 8-fold higher affinity than the (2S,3R)-MePhe3 diastereomer. Surprisingly, one analog with D-stereochemistry in residue 3, the (2R,3R)-MePhe3 analog, also displays high affinity for the delta receptor and is extraordinarily selective for this receptor. All analogs were agonists in the mouse vas deferens (MVD) and guinea pig ileum (GPI) smooth muscle bioassays, displaying MVD and GPI potencies consistent with their delta and mu opioid receptor affinities, respectively. The use of beta-MePhe as a replacement for Phe3 was based upon the desire to reduce the conformational flexibility of the Phe3 side chain by imposing a steric rotational constraint in the form of the beta-methyl substituent and to thus deduce the residue 3 side chain orientation in the delta receptor-bound conformation from the correlation between delta receptor binding affinities and conformational preferences. Molecular mechanics computations revealed, however, that the conformational constraints imposed by the beta-methyl group in the (2S,3S)-MePhe3 and (2S,3R)-MePhe3 analogs were too modest to allow unequivocal determination of delta receptor-bound residue 3 side chain conformation. However, analysis of the high-affinity (2R,3R)-MePhe3 analog revealed a strong preference for a single side chain conformer (chi 1 approximately 60 degrees). Low-energy conformers of this analog could only be effectively superimposed with low-energy conformers of the parent peptide in which the Phe3 side chain conformation was limited to chi 1 approximately -60 degrees. This observation eliminates the last remaining uncertainty regarding conformational features of the pharmacophore elements in the delta receptor-bound state, allowing the proposal of a complete model.

Development of a model for the delta opioid receptor pharmacophore. 1. Conformationally restricted Tyr1 replacements in the cyclic delta receptor selective tetrapeptide Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13)

A series of analogues of the conformationally restricted delta opioid receptor selective tetrapeptide Tyr-c[D-Cys-Phe-D-Pen]OH (JOM 13) was prepared in which the conformationally labile Tyr residue was replaced with several less flexible tyrosine analogues. Among these tyrosine analogues were the bicyclic structures 1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid (HO-Tic), 2-amino-6-hydroxytetralin-2-carboxylic acid (Hat), and 2-amino-5-hydroxyindan-2-carboxylic acid (Hai) in which rotations about the C alpha-C beta and C beta-C gamma bonds are restricted due to cyclization of the side chain to the backbone. Also examined were analogues in which tyrosine was replaced with either trans-3-(4'-hydroxyphenyl)proline (t-Hpp) or cis-3-(4'-hydroxyphenyl)proline (c-Hpp), residues in which rotations about C alpha-C beta, but not C beta-C gamma, are restricted. Both the t-Hpp1 and c-Hpp1 analogues displayed delta receptor binding affinity similar to the parent Tyr1-containing peptide, while the D-Hat1, L-Hat1, and L-Hai1 analogues exhibited somewhat lower affinity. The results observed for the t-Hpp1 and c-Hpp1 analogues are particularly significant since these two residues have little accessible conformational space in common. Since the binding conformation of residue 1 must be included in this limited conformational intersection, its elucidation is facilitated. Bioassay results from guinea pig ileum and mouse vas deferens preparations are in general agreement with the binding results; however some potency discrepancies are observed. These discrepancies may reflect different selectivities among delta receptor subtypes for the analogues or may represent differing efficacies among these conformationally restricted peptides. The conformational properties of the parent tetrapeptide and the residue 1-modified analogues were studied by molecular mechanics computations. All these peptides share a common rigid tripeptide cycle with a single energetically preferred backbone conformation and three different conformers of the D-Cys, D-Pen disulfide bridge, two of which are observed in the solid state and in aqueous solution, as previously determined from X-ray crystallography and 1H NMR spectroscopy data (Lomize, A; et al. J. Am. Chem. Soc. 1994, 116, 429-436). All the peptides have similar sets of low-energy conformations of their common flexible elements, the Phe3 side chain and the peptide group between the first residue and the rigid tripeptide cycle. However, possible conformations of the first residue differ and depend on the covalent constraints incorporated into the side chain.(ABSTRACT TRUNCATED AT 400 WORDS)

Fragmentation characteristics of neuropeptides related to chromogranin B and proenkephalin B using fast atom bombardment and collision-induced dissociation

This study deals with the mass spectral characterization of selected neuropeptides related to chromogranin B and proenkephalin B precursor proteins using fast atom bombardment (FAB) ionization in combination with low- and high-energy collision-induced dissociation. Fragmentation pathways were investigated using linked scan and tandem mass spectrometric techniques. First-order FAB mass spectra and product ion spectra of [M+H]+ ions are discussed and analysed for structure-specific information. In the high-energy product ion spectra, abundant y and c ions are found to be indicative of the presence of proline and threonine residues, respectively. With regard to side chain specific ions, diagnostic d and w ions are found, which support the presence of leucine, glutamic acid and glutamine at specific positions in the amino acid sequence.

Molecular cloning and characterization of the hamster preproenkephalin A cDNA

The cDNA for hamster preproenkephalin A (ENK) was cloned from an adrenal gland cDNA library constructed in the lambda ZapII vector. A nearly full-length cDNA was obtained and its 5' end region was completed using the technique of rapid amplification of cDNA ends (RACE). The coding and 3' untranslated regions of the hamster ENK cDNA share a high sequence identity with the rat, human, and bovine cDNAs, whereas the sequence identity is lower for the 5' untranslated region. Southern blot analysis of genomic DNA digests showed that a single copy of the ENK gene is present in the hamster haploid genome. Northern blot analysis of poly(A)+RNA from various hamster tissues indicated the following rank order for ENK messenger RNA abundance: adrenal glands > right atrium > brain > left atrium > right ventricle > ventricular septum > left ventricle, whereas primer extension analysis showed a single, identical transcriptional initiation site for the ENK mRNA in all these tissues. The sequence of the 5' untranslated region of the heart ENK cDNA was found to be identical to that from adrenal glands. This rules out the possibility that structural divergences in the 5' untranslated region of the heart ENK mRNA could decrease its translation efficiency and contribute to the very low level of enkephalin-containing peptides in the heart, compared to the adrenal glands.

Conversion of enkephalin and dermorphin into delta-selective opioid antagonists by single-residue substitution

The properties of di- and tri-peptides containing 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) in second position suggest that the message domain of opioid peptides can be composed of only two residues [Temussi, P. A., Salvadori, S., Amodeo, P., Guerrini, R., Tomatis, R., Lazarus, L. H., Picone, D. & Tancredi, T. (1994) Biochem. Biophys. Res. Commun. 198, 933-939]. As a crucial test of the possibility that the Tyr-Tic segment be a message domain in longer peptide sequences, we have inserted it in the sequences of two typical opioid peptides: [Leu]enkephalin, a non-selective agonist, and dermorphin, a selective mu agonist. Here we report the synthesis and biological activity of [L-Tic2]enkephalin, [L-Tic2]dermorphin, [L-Tic2]dermorphin carboxylic acid and [D-Tic2]dermorphin: all [L-Tic2]peptides were converted from agonists to delta-selective antagonists. The NMR conformational study in a dimethylsulfoxide/water cryoprotective mixture at low temperature shows diagnostic side-chain--side-chain NOEs in the spectra of all [L-Tic2]peptides and hints that the 90 degrees arrangement of the the two aromatic rings found in the cis-Tyr-L-Tic moiety, typical of N-methyl naltrindole and other delta-selective opiate antagonists, is responsible for the antagonist activity of all these peptides.