1H-NMR studies of receptor-selective substance P analogues reveal distinct predominant conformations in DMSO-d6

Analgesic Properties of Opioid/NK1 Multitarget Ligands with Distinct in Vitro Profiles in Naive and Chronic Constriction Injury Mice

The lower efficacy of opioids in neuropathic pain may be due to the increased activity of pronociceptive systems such as substance P. We present evidence to support this hypothesis in this work from the spinal cord in a neuropathic pain model in mice. Biochemical analysis confirmed the elevated mRNA and protein level of pronociceptive substance P, the major endogenous ligand of the neurokinin-1 (NK1) receptor, in the lumbar spinal cord of chronic constriction injury (CCI)-mice. To improve opioid efficacy in neuropathic pain, novel compounds containing opioid agonist and neurokinin 1 (NK1) receptor antagonist pharmacophores were designed. Structure-activity studies were performed on opioid agonist/NK1 receptor antagonist hybrid peptides by modification of the C-terminal amide substituents. All compounds were evaluated for their affinity and in vitro activity at the mu opioid (MOP) and delta opioid (DOP) receptors, and for their affinity and antagonist activity at the NK1 receptor. On the basis of their in vitro profiles, the analgesic properties of two new bifunctional hybrids were evaluated in naive and CCI-mice, representing models for acute and neuropathic pain, respectively. The compounds were administered to the spinal cord by lumbar puncture. In naive mice, the single pharmacophore opioid parent compounds provided better analgesic results, as compared to the hybrids (max 70% MPE), raising the acute pain threshold close to 100% MPE. On the other hand, the opioid parents gave poor analgesic effects under neuropathic pain conditions, while the best hybrid delivered robust (close to 100% MPE) and long lasting alleviation of both tactile and thermal hypersensitivity. The results presented emphasize the potential of opioid/NK1 hybrids in view of analgesia under nerve injury conditions.

Membrane-induced structure of the mammalian tachykinin neuropeptide gamma

Neuropeptide gamma (NPgamma) is a neurokinin-2 (NK-2) receptor selective agonist, which plays an important role in mediation of asthma and elicits a wide range of biological responses like bronchoconstriction, vasodepression and regulation of endocrine functions. The structure determination of this peptide agonist is important in understanding the molecular basis of peptide ligand recognition by the receptor and for rational drug design. In the present study we report the solution structure of NPgamma characterized by circular dichroism (CD) spectropolarimetry and 2D (1)H NMR spectroscopy in both aqueous and membrane mimetic solvents. Effect of calcium ions on the conformation of NPgamma was also studied using CD spectropolarimetry. Sequence-specific resonance assignments of protons have been made with the aid of correlation spectroscopy experiments and nuclear Overhauser effect spectroscopy experiments. The distance constraints obtained from the NMR data have been utilized to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that in water NPgamma prefers to be in an extended chain conformation whereas a helical conformation is induced in the central core and the C-terminal region of the peptide (K13-M21) in the presence of perdeuterated dodecylphosphocholine micelles, a membrane model system. A type II' beta turn from H9 to R11 precedes the helical core in the C-terminus of NPgamma. N-terminus of NPgamma also displays some degree of order and a possible turn structure. Conformation adopted by NPgamma in presence of lipid micelles represents a structural motif typical of NK-2 selective agonists and is similar to that observed for Neurokinin A in hydrophobic environment. The observed conformational features have been correlated to the binding ability and biological activity of NPgamma.

Three-dimensional structure of the mammalian tachykinin peptide neurokinin A bound to lipid micelles

The solution structure of NKA, a decapeptide of mammalian origin, has been characterized by CD spectropolarimetry and 2D proton nuclear magnetic resonance (2D 1H-NMR) spectroscopy in both aqueous and membrane mimetic solvents. Unambiguous NMR assignments of protons have been made with the aid of correlation spectroscopy (DQF-COSY and TOCSY) experiments and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The distance constraints obtained from the NMR data have been utilized to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that in water NKA prefers to be in an extended chain conformation whereas a helical conformation is induced in the central core and the C-terminal region (D4-M10) of the peptide in the presence of perdeuterated dodecylphosphocholine (DPC) micelles, a membrane model system. Though less defined the N-terminus also displays some degree of order and a possible turn structure. The conformation adopted by NKA in the presence of DPC micelles represents a structural motif typical of neurokinin-2 selective agonists and is similar to that reported for eledoisin in hydrophobic environment.

Novel consecutive beta- and gamma-turn mimetics composed of alpha-aminooxy tripeptides

[structure: see text] To develop novel consecutive beta- and gamma-turn mimetics, we designed and characterized alpha-aminooxy tripeptides (trimers) consisting of oxanipecotic acid dimer and alpha-aminooxy acid. According to FT-IR and NMR data, as well as ab initio quantum calculations, the trimers adopted unusual folded structures with consecutive beta- and gamma-turnlike conformations.

Solution structure of the tachykinin peptide eledoisin

Both the aqueous and the lipid-induced structure of eledoisin, an undecapeptide of mollusk origin, have been studied by two-dimensional proton nuclear magnetic resonance spectroscopy and distance geometry calculations. Unambiguous nuclear magnetic resonance assignments of protons have been made with the aid of correlation spectroscopy experiments and nuclear Overhauser effect spectroscopy experiments. The distance constraints obtained from the nuclear magnetic resonance data have been utilized in a distance geometry algorithm to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that, while in water and dimethyl sulfoxide, eledoisin prefers to be in an extended chain conformation, whereas in the presence of perdeuterated dodecylphosphocholine micelles, a membrane model system, helical conformation is induced in the central core and C-terminal region (K4-M11) of the peptide. N terminus, though less defined, also displays some degree of order and a possible turn structure. The conformation adopted by eledoisin in the presence of dodecylphosphocholine micelles is similar to the structural motif typical of neurokinin-2 selective agonists and with that reported for kassinin in hydrophobic environment.

Lipid induced conformation of the tachykinin peptide Kassinin

Both the aqueous and lipid-induced structure of Kassinin, a dodecapeptide of amphibian origin, has been studied by two-dimensional proton nuclear magnetic resonance (2D 1H-NMR) spectroscopy and distance geometry calculations. Unambiguous NMR assignments of protons have been made with the aid of correlation spectroscopy (DQF-COSY and TOCSY) experiments and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The distance constraints obtained from the NMR data have been utilized in a distance geometry algorithm to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that, while in water Kassinin prefers to be in an extended chain conformation, in the presence of perdeuterated dodecylphosphocholine (DPC) micelles, a membrane model system, helical conformation is induced in the central core and C-terminal region (K4-M12) of the peptide. N-terminus though less defined also displays some degree of order and a possible turn structure. The conformation adopted by Kassinin in the presence of DPC micelles is consistent with the structural motif typical of neurokinin-1 selective agonists and with that reported for Eledoisin in hydrophobic environment.

Characterization of substance P-membrane interaction by transferred nuclear Overhauser effect

Substance P, one of the mammalian tachykinins, is known to interact strongly with lipid bilayers and this interaction may play a role in the receptor-peptide recognition process. The conformation of substance P bound to vesicles consisting of perdeuterated phosphatidylcholine has been investigated by means of two-dimensional transferred nuclear Overhauser (trNOE) spectroscopy. Nuclear magnetic resonance data analysis resulted in a unique conformational family characterized by a well-defined conformation of the last seven C-terminal amino acids, which consists of a sequence of nonstandard turns following each other in a helix-like manner. The absence of short- or medium-range trNOE in the N-terminal part indicates its structural flexibility.

NMR and molecular dynamics studies of tachykinins: conformation of substance P fragment 4-11

The conformation of the C-terminal octapeptide fragment of Substance P (SP4-11, Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2) has been investigated by 2D-NMR and MD methods. The octapeptide exists in a blend of conformations. The molecule seems to shuttle between conformations with gamma-bends either at Phe5 or Gly6 or Gln3 or Leu7 and between a nearly extended structure.

Membrane-induced secondary structures of neuropeptides: a comparison of the solution conformations adopted by agonists and antagonists of the mammalian tachykinin NK1 receptor

We present what we believe to be the first documented example of an inducement of distinctly different secondary structure types onto agonists and antagonists selective for the same G-coupled protein receptor using the same membrane-model matrix wherein the induced structures are consistent with those suggested to be biologically active by extensive analogue studies and conventional binding assays. 1H NMR chemical shift assignments for the mammalian NK1 receptor-selective agonists alpha-neurokinin (NKA) and beta-neurokinin (NKB) as well as the mammalian NK1 receptor-selective antagonists [d-Pro2,d-Phe7,d-Trp9]SP and [d-Arg1, d-Pro2,d-Phe7,d-His9]SP have been determined at 600 MHz in sodium dodecyl sulfate (SDS) micelles. The SDS micelle system simulates the membrane-interface environment the peptide experiences when in the proximity of the membrane-embedded receptor, allowing for conformational studies that are a rough approximation of in vivo conditions. Two-dimensional NMR techniques were used to assign proton resonances, and interproton distances were estimated from the observed nuclear Overhauser effects (NOEs). The experimental distances were used as constraints in a molecular dynamics and simulated annealing protocol using the modeling package DISCOVER to generate three-dimensional structures of the two agonists and two antagonists when present in a membrane-model environment to determine possible prebinding ligand conformations. It was determined that (1) NKA is helical from residues 6 to 9, with an extended N-terminus; (2) NKB is helical from residues 4 to 10, with an extended N-terminus; (3) [d-Pro2,d-Phe7,d-Trp9]SP has poorly defined helical properties in the midregion and a beta-turn structure in the C-terminus (residues 6-9); and (4) [d-Arg1,d-Pro2, d-Phe7,d-His9]SP has a helical structure in the midregion (residues 4-6) and a well-defined beta-turn structure in the C-terminus (residues 6-10). Attempts have been made to correlate the observed conformational differences between the agonists and antagonists to their binding potencies and biological activity.

Lipid-induced conformation of substance P

Both the aqueous and the lipid-induced structure of a representative and widely studied tachykinin, substance P, has been investigated by two-dimensional proton nuclear magnetic resonance (2D 1H-NMR) spectroscopy and distance geometry calculations. Unambiguous NMR assignments of protons have been made with the aid of correlation spectroscopy (COSY and TOCSY) experiments and Overhauser enhancement spectroscopy (ROESY and NOESY; experiments. The NMR data obtained were utilized in a distance geometry algorithm to generate a family of structures which were further refined using restrained energy minimization. These data show that, while in water substance P appears to favour an extended chain conformation, in the presence of perdeuterated dodecylphosphocholine (DPC) micelles as membrane model system an amphiphilic helical conformation is induced in the mid-region (Q5-Q8) of substance P. The conformation adopted by substance P in the presence of DPC micelles yields a structural motif typical of neurokinin-1 selective ligands, as proposed by Convert and coworkers (O. Convert et al., Neuropeptides 19, 259-270 (1991)).

Synthesis and biological activity of NK-1 selective, N-backbone cyclic analogs of the C-terminal hexapeptide of substance P

The application of the concept of backbone cyclization to linear substance P (SP) analogs is presented. We describe the synthesis, characterization, and biological activity of a series of backbone-to-amino-terminus cyclic analogs of the C-terminal hexapeptide of SP. These analogs were designed on the basis of NMR data and molecular modeling of the selective NK-1 analog WS-septide (Ac[Arg6,Pro9]SP6-11). A series of peptides with the general formula: cyclo[-CH2)m-NH-CO-(CH2)n-CO-Arg-Phe-Phe-N-]-CH2-CO-Leu-Met-NH2 (n = 2, 3, 6 and m = 2, 3, 4) was synthesized by solid phase methodology using Fmoc chemistry for the main chain and Boc chemistry for the building units [Na-(omega-aminoalkyl)Gly] side chains. Cyclization was performed on the resin after removal of the Boc protecting group from the omega-aminoalkyl chain. Cyclic and precyclic analogs were compared. They were purified by HPLC and characterized by mass spectroscopy and NMR. Biological activity and selectivity to the NK-1 neurokinin receptor were found to depend on cyclization and the ring size: The most active and selective analog had a ring of 20 atoms. This analog was found to have enhanced metabolic stability in various tissue preparation compared to WS-septide.

NMR and molecular modeling investigations of the neuropeptide substance P in the presence of 15 mM sodium dodecyl sulfate micelles

To better understand the structural basis of the biological activity of the neuropeptide substance P SP; (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2), two-dimensional nmr spectroscopy experiments and simulated annealing calculations were used to investigate the conformation adopted in the presence of the membrane model system sodium dodecyl sulfate. It was determined that SP in the presence of SDS micelles undergoes a conformational equilibrium between an alpha- and a 3(10)-helix involving the midregion (Pro4-Gln5-Gln6-Phe7-Phe8) of the peptide. The C-terminus adopts an extended conformation while the N-terminus remains quite flexible. The conformation adopted by SP in the presence of SDS micelles yields a structure that is consistent with the model of a neurokinin-1 selective ligand proposed by Convert.

Solution conformation of a cyclic neurokinin antagonist: a NMR and molecular dynamics study

The solution structure of a hexapeptide, cyclo (Gln-Trp-Phe-Gly-Leu-Met), which is a selective NK-2 antagonist, has been studied by a combination of two-dimensional nmr and molecular dynamics (MD) techniques. The simulation based on nmr and MD data resulted in the convergence to a family of structures. Free molecular dynamics for 50 ps in the presence of DMSO solvent molecules shows that the structure is energetically stable. One intramolecular hydrogen bond between the amide proton of Gln and the carbonyl oxygen of Gly was revealed. This result is consistent with the results from the measurement of the temperature coefficient of the amide protons. The extent of intermolecular hydrogen bonding between the amide protons of the peptide and DMSO was also revealed by the free MD simulation. The resulting structure of the cyclic peptide contains a variation type I' beta-turn in the Gly-Leu-Met-Gln segment. Comparison of the structure of this peptide with that of other NK-2 antagonist cyclic hexapeptides was made, and the activity of cyclic antagonists appears to be inversely related to the conformational rigidity of the cyclic peptides.

Solution conformation study of substance P methyl ester and [Nle10]-neurokinin A (4-10) by NMR spectroscopy

High-resolution proton spectra at 500 MHz of two tachykinin peptides, substance P methyl ester (SPOMe) and [Nle10]-neurokinin A (4-10), have been obtained in dimethylsulfoxide (DMSO), and for SPOMe, also in 2,2,2-trifluoroethanol (TFE)/water mixtures. Complete chemical shift assignments for these peptides were made based on two-dimensional (2D) nmr techniques, correlated spectroscopy and total COSY. J coupling measurement and nuclear Overhauser effect spectroscopy (NOESY) were then used to determine the conformation of these peptides in the various solvents. Based on the J coupling, NOE correlations, and temperature coefficients of the NH resonances, it is concluded that these two peptides exist in DMSO at room temperature as a mixture of conformers that are primarily extended. For SPOMe in TFE/water with high TFE content, however, helical structures are found to be present, and they become quite clear at temperatures between 270 and 280 K. The variation of the 13C chemical shifts of the C alpha (the secondary shift) with TFE contents corroborates this conclusion. The NOE and C alpha shifts show that the main helical region for SPOMe lies between 4P and 9G. The C-terminus segment L-M-NH2 is found to be quite flexible, which appears to be quite common for neurokinin-1 selective peptides.

Determination of the solution structure of neuropeptide K by high-resolution nuclear magnetic resonance spectroscopy

1H NMR chemical shift assignments for neuropeptide K (NPK) and neurokinin A (NKA) have been determined at 600 MHz in 28% trifluoroethanol/water solution. Two-dimensional NMR techniques were used to assign proton resonances, and interproton distances were estimated from the observed nuclear Overhauser effects (NOEs). These distances were used as constraints in a simulated annealing protocol within the program XPLOR to generate structures consistent with experimental data. NPK forms a regular amphipathic alpha-helical structure from Asp 3, terminating at Gly 18. Slowly exchanging amide protons identified in this region are likely to be involved in hydrogen bonds to stabilize the helix. The remainder of the molecule displays many sequential NOEs, with some i-(i + 2) contacts, but little further evidence of defined secondary conformation. NKA displays strong sequential connectivities between amide protons from Thr 3 to Met 10, and some i-(i + 2) connectivities suggestive of a series of dynamic turns in equilibrium. A comparison of the tail region of NPK with the related peptide homologue, neurokinin A, in the same solvent system, indicates that both show increasing order when trifluoroethanol is titrated into water solution, with the appearance of sequential NOEs between backbone amide protons. Differences between the corresponding spans of primary sequence appear to be minimal. The clear finding that NPK adopts a well-defined helix in its N-terminal half and is relatively disordered in the C-terminal half, which includes the entire NKA sequence, may have important implications for understanding the increased selectivity of NPK over NKA for one class of neurokinin receptor.

Synthesis, biological activity, and conformational analysis of [pGlu6,N-MePhe8,Aib9] substance P (6-11): a selective agonist for the NK-3 receptor

A highly potent and selective agonist to the tachykinin NK-3 receptor, [pGlu6,N-MePhe8,Aib9] substance P (6-11) (I), was synthesized via the solid phase method. The ED50 of I was 4 nM in the guinea pig ileum in the absence of atropine (NK-1+NK-3 receptors) and this agonist was 5000-fold less potent in the presence of atropine (NK-1 receptor). The analogue was virtually inactive in the rat vas deferens (NK-2 receptor). A detailed analysis of the solution conformation of this analogue in DMSO-d6 and in a DMSO-d6/H2O cryomixture was carried out by a combination of 1H-nmr 2D techniques (DQF-COSY, TOCSY, NOESY and ROESY) and model building based on empirical energy calculations. Peptide I exists as a mixture of isomers containing cis and trans Phe-N-MePhe peptide bonds. The main isomer, containing a cis Phe-N-MePhe peptide bond, shows a preferred folded conformation characterized by a type VI beta-turn with Phe and N-MePhe in the i + 1 and i + 2 positions. The turn is followed by a helical segment extending to the C-terminal. This conformation is compared to previously reported conformations of other selective tachykinin agonists and may be a promising lead for the design of novel NK-3 agonists with additional conformational constraints.

Design, synthesis and conformational analysis of gamma-turn peptide mimetics of bradykinin

Gamma-turns are regular secondary structure elements, found with some frequency in small peptides, that have been implicated in the biologically active conformations of several systems. This report describes the design, synthesis and conformational analysis of a non-peptide gamma-turn mimetic. Low energy conformations of the mimetic system exhibit good conformational agreement with an experimentally observed peptide gamma-turn. The mimetics were incorporated into the nonapeptide bradykinin, for which a gamma-turn, formed by residues Ser 6 to Phe 8, has been hypothesized to be a bioactive conformation. The results indicate that a bioactive conformation of bradykinin may include a reverse turn at this position.

Conformation-activity relationship of tachykinin neurokinin A (4-10) and of some [Xaa8] analogues

NKA (4-10), the C-terminal heptapeptide fragment (Asp-Ser-Phe-Val-Gly-Leu-Met-NH2) of tachykinin NKA, is more active than the parent native compound in the interaction with the NK-2 receptor. Substitution of Gly8 with the more flexible residue beta-Ala8 increases its selectivity with respect to other two known receptors (NK-1 and NK-3), whereas substitution with either D-Ala8 or GABA8 deprives the peptide of its biological activity. These findings can be interpreted by a conformational analysis based on NMR studies in DMSO-d6 and in a DMSO-d6/H2O cryoprotective mixture combined with internal energy calculations. NKA(4-10) is characterized by a structure containing a type I beta-turn extending from Ser5 to Gly8, followed by a gamma-turn centered on Gly8, whereas for [beta-Ala8]NKA(4-10) is possible to suggest a type I beta-turn extending from Ser5 to beta-Ala8, followed by a C8 turn comprising beta-Ala8 and Leu9 and by another beta-turn extending from beta-Ala8 to the terminal NH2. The preferred conformation of [beta-Ala8]NKA(4-10) is not compatible with models for NK-1 and NK-3 agonists proposed on the basis of rigid peptide agonists [Levian-Teitelbaum et al. (1989) Biopolymers 28, 51-64; Sumner & Ferretti (1989) FEBS Lett. 253, 117-120]. The preferred solution conformation of [beta-Ala8]NKA(4-10) may thus be considered as a likely bioactive conformation for NK-2 selective peptides.

Backbone cyclization: A new method for conferring conformational constraint on peptides

This article describes a new concept of medium- and long-range cyclization of peptides through "backbone cyclization." In this approach, conformational constraints are conferred on a peptide by linking omega-substituted alkylidene chains replacing N(alpha) or C(alpha) hydrogens in a peptidic backbone. Backbone cyclization, which is divided into N-backbone and C-backbone cyclizations, allow for new modes of cyclization in addition to the classical ones that are limited to cyclization through the side chains and/or the amino or carboxyl terminal groups. The article also describes the application of the N-backbone cyclization to the active region of substance P. Conformational constraints of this peptide by the classical cyclization modes led to inactive analogues whereas N-backbone cyclization provided an active, selective, and metabolically stable analogue.

Synthesis and purification of two SP (6-11) analogues with enhanced selectivity for the NK-1 receptor

Two hexapeptide analogues of Substance P (6-11) have been synthesized. Replacement of Gly9 by proline provides a peptide with tenfold enhanced selectivity for the NK-1 receptor. The corresponding proline-containing glycopeptide incorporating a beta-D-glucopyranosyl residue linked to the side-chain of Glu6 was 100 times more selective than Substance P for the same receptor.