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R Tomatis

Publications and source records attributed to R Tomatis.

At least 19 recordsLinked to original sources
PubMed1997

Synthesis and pharmacological activity of deltorphin and dermorphin-related glycopeptides.

The solid phase procedure, based on the Fmoc chemistry, was used to prepare some opioid deltorphin (H-Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2, DEL C) and dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2, DER) analogues in which a D-glucopyranosyl moiety is beta-O-glycosidically linked to a Thr4 or Thr7 side chain. Their activities were determined in binding studies based on displacement of mu- and delta-receptor selective radiolabels from rat brain membrane synaptosomes, in guinea pig ileum and rabbit jejenum bioassays, and, in vivo, by a mouse tail-flick test after intracerebroventricular (icv) and subcutaneous (sc) administrations. The glyco analogues modified at position 4 displayed low opioid properties, while Thr7-glycosylated peptides retained high delta- or mu-selectivity and remarkable activity in vivo. In particular, as systemic antinociceptive agents, the latter glucoside-bearing compounds were more potent than the parent unglycosylated peptide counterparts, showing a high blood to brain rate of influx which may be due to the glucose transporter GLUT-1.

Amino Acid Sequence↗
PubMed1997

Helix-inducing alpha-aminoisobutyric acid in opioid mimetic deltorphin C analogues.

The achiral symmetric alpha-aminoisobutyric acid (Aib) replaced the critical N-terminal residues of the amphibian skin opioid deltorphin C (H-Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2) without detriment to the physicochemical requirements for delta opioid receptor recognition. Substitutions by the alpha, alpha-dialkyl amino acid in place of D-Ala2 or Phe3, or both, exhibited high delta receptor affinity (Ki delta = 0.12-3.6 nM) and 5-9-fold greater selectivity (Ki mu/Ki delta = 5000-8500) than the parent compound. This is the first definitive demonstration that the D-chirality of alanine and the aromaticity of phenylalanine are replaceable by an achiral alpha, alpha-dialkylated residue without detrimental effects on ligand binding. Incorporation of the mono-alpha-alkyl amino acid L- or D-Ala at the third position also produced highly selective delta ligands (Ki mu/Ki delta = 2000-3500), albeit with reduced delta affinities (Ki delta = 6-15 nM). Replacement of the anionic residue Asp4 by Aib yielded an opioid peptide that fit two-site binding models for the delta receptor (eta = 0.763; P < 0.0001) and displayed dual high affinity for both delta and mu receptors, emphasizing the repulsive effect by a negative charge at mu receptor sites and the insignificance of Asp for delta affinity. Molecular dynamics conformation analyses suggested that Aib residues caused distinct changes in deltorphin C secondary structure when substituted for D-Ala2, Asp4, and simultaneously D-Ala2 and Phe3 but not when substituted for Phe3. These conformational changes might be critical factors for the proper orientation of reactive constituents of residues in the N-terminal region of deltorphin C. Disparities between binding data and functional bioassays of [Aib3] indicated that Phe3 was required for bioactivity in mouse vas deferens but not for interaction with delta opioid receptors in rat brain membranes.

Amino Acid Sequence↗
PubMed1997

HIV-1 protease inhibitors containing a novel C2 symmetrical hydroxyalkylgem-diamino core structure.

Two series of peptidomimetics containing a novel C2 symmetrical hydroxyalkylgem-diamino core structure were prepared, from amino acid starting materials, and evaluated as inhibitors of HIV-1 protease (HIV-1 Pr). 1,1-Diamino-3-hydroxypropane (gHse) derivatives showed weak inhibitory potency (IC50 > 10 microM). In the 1,1-diamino-2-hydroxyethane (gSer) series, a compound containing P1/P1' benzyl and P2/P2'Fmoc substituents, displayed a significant HIV-1 Pr inhibition (IC50 = 440 nM).

Amino Acid Sequence↗
PubMed1997

Opioid diketopiperazines: synthesis and activity of a prototypic class of opioid antagonists.

Discovery of high affinity and ultraselective delta opioid dipeptide antagonists composed of 2',6'-dimethyl-L-tyrosyl (Dmt) and 1,2,3,4-tetrahydroisoquinoline-3-carboxylic (Tic) served as the basis for the conformationally restricted diketopiperazine cyclo(Dmt-Tic) and related open chain analogues. These peptides primarily bind to delta opioid receptors: c(Dmt-Tic) displayed 30- to 50-fold higher delta affinity (Ki delta) than its diastereo-isomeric analogues and more than 4000-fold greater than its Tyr cognate; all of the c(Tyr-Tic) analogues were essentially inactive; c[(N-methyl)Dmt-Tic] lost 5-fold in Ki delta, while Ki mu increased 10-fold to yield a nonselective peptide; and the c(Dmt-Phe) series exhibited considerably reduced binding which indicated a synergism between Dmt and Tic in the binding mechanism. Whereas acetyl-Dmt-Tic linear peptides weakly interacted with opioid receptors, Ac-Dmt-Tic-NH2, exhibited better delta antagonist activity than c(Dmt-Tic) and greater delta receptor selectivity (Ki mu/Ki delta = 570). A three point attachment hypothesis for the interaction between c(Dmt-Tic) and the delta receptor was proposed: hydrophobicity imparted by the aromatic rings and the methyl groups of Dmt, hydrogen bonding through the tyramine hydroxyl group, and cation-pi interactions were suggested as contributing factors in binding the diketopiperazine in the receptor pocket. Although c(Dmt-Tic) exhibited a weak antagonist activity with mouse vas deferens, this diketopiperazine may provide a scaffolding for the formation of more potent antagonists for potential therapeutic applications.

Animals↗
PubMed1997

Opioid diketopiperazines: refinement of the delta opioid antagonist pharmacophore.

Bioactive models for a delta opioid receptor antagonist are proposed based on the structurally rigid, diketopiperazine containing cyclo 2',6'-dimethyl-L-tyrosyl (Dmt)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). Monte Carlo conformational analysis of c(Dmt-Tic) generated three low energy clusters (I-III) of conformers. The lowest energy conformer representing cluster I superimposed best with the X-ray crystal structures of c(Tyr-Tic), an inactive diketopiperazine with similar framework as c(Dmt-Tic), with H-Tyr-Tic-NH2, a dipeptide of moderate delta opioid affinity and lacking bioactivity, and with H-Tyr-Tic-Phe-Phe-OH (TIPP), a selective and potent delta opioid receptor antagonist. Clusters I and II superimposed best with three different overlays of naltrindole, a potent delta opiate antagonist, and with two other H-Tyr-Tic-NH delta opioid antagonist pharmacophores proposed by Temussi et al. (1994) and Wilkes and Schiller (1995). The 3-dimensional topography of these two clusters of c(Dmt-Tic) conformations may represent bioactive models for interaction of an antagonist at delta opioid receptors. Cluster I conformers exhibited gauche- (- 64 degrees) and gauche+ (53 degrees) orientations of the side chains Dmt and Tic, respectively, while cluster II contained trans (179 degrees) and gauche+ (62 degrees) orientations of those side-chains. Aromatic ring distances were 5.4 A for cluster I conformations and 8.2 A for cluster II structures. Orientation about the peptide bond N-C' was cis (- 5 degrees and 3 degrees) for both clusters, respectively. These structural features may provide optimal alignment of the physicochemical moieties important for delta opioid receptor interaction, such as the hydrophobic methyl groups of Dmt, hydrogen bonding of the dimethyltyrosine hydroxyl group within the receptor pocket and cation-pi interactions involving the aromatic rings of Dmt and Tic, as profiled by the three point attachment hypothesis.

Diketopiperazines↗
PubMed1996

Polymorphonuclear neutrophils pulsed with synthetic peptides efficiently activate memory cytotoxic T lymphocytes.

Polymorphonuclear neutrophils (PMNs), traditionally considered effector cells in the inflammatory response, have recently been regarded as potential regulators of the immune response. In the present study we investigate whether PMNs are efficient antigen-presenting cells for reactivation of memory cytotoxic T lymphocytes (CTLs). PMNs were pulsed with synthetic peptides derived from Epstein-Barr virus (EBV) antigens. We have used the IVTDFSVIK (IVT) peptide derived from the Epstein-Barr virus-encoded nuclear antigen 4 protein, corresponding to the immunodominant epitope of HLA-AII-restricted CTL responses, and the CLGGLLTMV (CLG) peptide derived from the latent membrane protein 2 antigen, representing a subdominant epitope of HLA-A2-restricted CTL responses. The data indicate that peptide-pulsed PMNs selectively activate specific CTL responses to both immunodominant and subdominant epitopes. The efficiency of CTL induction by PMNs was comparable to that observed with the conventional method of EBV-specific CTL reactivation with the autologous lymphoblastoid cell line, as well as with peptide-pulsed monocyte-enriched adherent cells. On the contrary, unactivated peptide-pulsed lymphocytes failed to induce an epitope-specific CTL response. These results demonstrate that PMNs efficiently present antigens to memory virus-specific CTLs and suggest that they may have a role as antigen-presenting cells.

Amino Acid Sequence↗
PubMed1996

Activation of epitope-specific memory cytotoxic T lymphocyte responses by synthetic peptides.

Cytotoxic T lymphocytes (CTL) recognize antigens as short peptides selected for presentation by their ability to bind to MHC class I molecules. Polyclonal Epstein-Barr virus (EBV)-specific memory CTL responses, reactivated from blood lymphocytes of HLA-A11-positive individuals by stimulation with the autologous EBV-transformed lymphoblastoid cell line (LCL), are often dominated by reactivites directed to the peptide epitope IVTDFSVIK (IVT), corresponding to amino acids 416-424 of EBV nuclear antigen-4 (EBNA4). We now report the selective activation of IVT-specific CTL by stimulation of lymphocytes with the corresponding synthetic peptide. A more than 10-fold increase in frequency of CTL clones with this specificity (from 8% to 96%) was obtained when the peptide was presented by HLA-A11-transfected T2 cells (T2/A11). Titration of synthetic peptide in cytotoxic assay demonstrated that clones activated under these conditions are as efficient as clones activated by conventional LCL stimulations. Induction of memory CTL responses required low surface density of MHC: peptide complexes, since reactivation was achieved by stimulation with T2/A11 cells pulsed with concentrations of peptide that are suboptimal for induction of target cell lysis. This protocol of activation revealed the presence of IVT-specific CTL precursors in a donor that failed to mount an IVT-specific response upon stimulation with the autologous B95.8 virus-transformed LCL. The results suggest that stimulation with synthetic peptide epitopes can be efficiently used for induction of memory CTL responses, and may be particularly helpful for the selective expansion of subdominant CTL specificities.

Amino Acid Sequence↗
PubMed1995

Calmodulin binding sites of the skeletal, cardiac, and brain ryanodine receptor Ca2+ channels: modulation by the catalytic subunit of cAMP-dependent protein kinase?

In this study, we define calmodulin binding sites of skeletal, cardiac, and brain ryanodine receptor (RYR) Ca2+ channels. Cardiac and brain RYR peptides corresponding to the calmodulin binding sites present in the skeletal RYR [Menegazzi, P., et al. (1994) Biochemistry 33, 9078-9084] were synthesized, and their interaction with calmodulin was monitored by fluorescent techniques. The central portions of the skeletal, cardiac, and brain RYR protomers display one high (CaM1; Kd ranging between 2.7 and 10.2 nM) and one low affinity (CaM2; Kd ranging between 116 and 142 nM) calmodulin binding site. Depending on the RYR model having 4 or 12 transmembrane segments, a third calmodulin binding site (CaM3) was identified a few residues upstream from the putative transmembrane segment M1 or M5. Its affinity for calmodulin varied between the RYR isoforms: the cardiac RYR CaM3 displays a high affinity (9.09 +/- 1.0 nM, n = 5), while the skeletal and brain RYR CaM3 have low affinity, the lowest affinity being displayed by the brain isoform (234 +/- 39 nM, n = 3). The RYRs calmodulin binding site CaM1 encompasses the sequence Arg-His-Arg-Val(Ile)-Ser-Leu, which is phosphorylated in vitro by the catalytic subunit of the cAMP-dependent protein kinase. Phosphorylation of RYR PM1 peptides occurs on the Ser, corresponding to amino acid number 2919, 3020, and 3055 of the brain, cardiac, and skeletal RYR protomers, respectively. We found that phosphorylation of the RYR PM1 peptides was inhibited by calmodulin binding and that the formation of the PM1 peptide-calmodulin complex was inhibited by peptide phosphorylation. These data indicate that the effect of calmodulin binding to RYR CaM1 may be regulated by the phosphorylation state of the Ser residue localized within the sequence Arg-His-Arg-Val(Ile)-Ser-Leu.

Amino Acid Sequence↗
PubMed1995

Effect of anchor residue modifications on the stability of HLA-A11/peptide complexes.

MHC class I antigens bind peptides derived from endogenous proteins and present them to cytotoxic T lymphocytes. This binding is selective and shows high allele specificity. Peptides binding to HLA-A11 contain a hydrophobic or a small polar amino acid at position 2 and a lysine at the carboxy terminus. Peptide analogues, derived from previously identified high affinity peptides and carrying amino acid substitutions in position 2, were used to determine the requirements for formation of stable HLA-A11/peptide complexes. By kinetic analysis we were able to discriminate among apparent and true binders. Only analogues carrying in position 2 the amino acids valine, threonine and isoleucine formed stable complexes with HLA-A11 with a half life > or = 72 hours.

Amino Acid Sequence↗
PubMed1995

Effects of peptide T derivatives on the proliferation of cultured human keratinocytes.

[D-Ala1]peptideT-amide, the linear hexapeptide H-Thr-Hse-Asn-Tyr-Thr-Asp-OH (LPT) and its cyclic analog, cyclo(-Thr-Hse-Asn-Tyr-Thr-Asp-) (CPT), were tested for their effects on the proliferation of cultured normal human keratinocytes (KTs) in comparison with vasoactive intestinal peptide (VIP). [D-Ala1]PT-NH2, LPT and VIP (all 0.1 mumol/l) increased the cell number in KT cultures, whereas CPT was ineffective. The VIP antagonist [N-Ac-Tyr1,D-Phe2]GRF (1-29)-NH2 significantly inhibited the VIP effects on KTs. On the other hand this antagonist did not affect the peptide T (PT) compounds-induced stimulation of KTs, providing indirect evidence that the mitogenic effects of VIP and PT peptides are probably mediated via different receptors.

Adenosine↗
PubMed1994

A bioactive fullerene peptide.

The highly hydrophobic C60 (buckminsterfullerene) was water solubilized by covalently linking the synthon 1,2-dihydro-1,2-methanofullerene [60]-61-carboxylic acid to the alpha-amino group of the hydrophilic 4-8 sequence of peptide T, known to display potent human monocyte chemotaxis. The resulting compound, characterized by a variety of analytical techniques, including a UV spectrum in aqueous solution, exhibits remarkable chemotactic potency, comparable to that of the parent pentapeptide. Furthermore, this fullerene-peptide conjugate inhibits, albeit weakly, HIV-1 protease.

Amino Acid Sequence↗
PubMed1994

Selective opioid dipeptides.

The surprising change of selectivity induced by the change of chirality in peptides containing the tetrahydro-3-isoquinoline carboxylic acid (Tic) in second position, interpreted as a conformational preference induced on the Tyr-Xaa-Phe domain, can instead be attributed to the Tyr-Tic message domain. The relative spatial disposition of the aromatic ring of delta-selective non peptidic opiates is compatible with a message domain, in opioid peptides, of only two residues. This hypothesis was tested through the synthesis of Tyr-L-Tic-NH2, Tyr-D-Tic-NH2, Tyr-L-Tic-Ala-NH2, Tyr-L-Tic-Ala-OH and Tyr-D-Tic-Ala-NH2. Peptides containing Tyr-L-Tic- behave as very selective delta antagonists and those containing Tyr-DTic- as non selective agonists. This is the first case of opioid peptides containing a two-residue message domain and of opioid dipeptides with substantial opioid activity.

Amino Acid Sequence↗
PubMed1994

Synthesis and biological activity of D-glucopyranosyl peptide T derivatives.

The solid phase procedure, based on the Fmoc (9-fluorenylmethyloxycarbonyl) chemistry, was used to prepare some peptide T analogues in which D-glucopyranosyl units are beta-O-glycosidically linked to Thr4 and/or Thr5 side chains. All glycopeptides showed significant human monocyte chemotaxis and high resistance to degradation by plasma or brain enzymes.

Amino Acid Sequence↗
PubMed1993

Relationship between receptor affinity and topography of N-terminally extended and bridged [Tyr1-->Asp4]deltorphin C analogues: novel probes for the delta-opioid receptor.

Receptor binding of N-terminally extended Tyr1 deltorphin C analogues diminished delta and mu affinities, but with only a moderate loss in delta selectivity. Pseudopeptide bridged [Tyr1-->Aps4]deltorphin C analogues drastically decreased delta affinity to yield peptides with poor delta selectivity. Low energy conformers of the peptides revealed that the bridge modifies the spatial orientation of the backbone of the N- and C-terminal sequences with respect to deltorphin C. The data indicate that the delta receptor site can accommodate an opioid peptide containing an N-terminal aliphatic extension on amino-Tyr1, but not a heptapeptide conformationally constrained between residues 1 and 4.

Amino Acid Sequence↗
PubMed1993

Structure-activity relationships of cyclic and linear peptide T analogues.

Using the potent cyclic peptide T analog [formula: see text] as parent compound, a series of analogues were synthesized and their potencies in a monocyte chemotaxis assay were compared with those of correspondingly modified linear peptides. Structure-activity relationships observed with cyclic compounds did not always parallel those determined with linear analogues. [formula: see text] showed the highest affinity to CD4 receptor of monocytes of any peptide thus far studied. It also proved to be highly resistant to degradation by plasma or brain enzymes.

Amino Acid Sequence↗
PubMed1993

Studies on the anti-phospholipase A2 and anti-inflammatory activities of a uteroglobin fragment and related peptides.

The nonapeptide antiflammin P1 (H-Met-Gln-Met-Lys-Lys-Val-Leu-Asp-Ser-OH), its isoAsp8 analogue and the corresponding aminosuccinyl peptide were prepared, characterized and tested for inhibition of phospholipase A2 (PLA2) in vitro and for anti-inflammatory activity in vivo under assay conditions recently recommended. All peptides are devoid of PLA2 inhibitory and anti-inflammatory activity.

Amino Acid Sequence↗