Structure-affinity studies of C-terminally modified analogs of neuropeptide Y led to a novel class of peptidic Y1 receptor antagonist

Receptor-specific recognition of NPY peptides revealed by structures of NPY receptors

In response to three highly conserved neuropeptides, neuropeptide Y (NPY), peptide YY, and pancreatic polypeptide (PP), four G protein-coupled receptors mediate multiple essential physiological processes, such as food intake, vasoconstriction, sedation, and memory retention. Here, we report the structures of the human Y₁, Y₂, and Y₄ receptors in complex with NPY or PP, and the G_i1 protein. These structures reveal distinct binding poses of the peptide upon coupling to different receptors, reflecting the importance of the conformational plasticity of the peptide in recognizing the NPY receptors. The N terminus of the peptide forms extensive interactions with the Y₁ receptor, but not with the Y₂ and Y₄ receptors. Supported by mutagenesis and functional studies, subtype-specific interactions between the receptors and peptides were further observed. These findings provide insight into key factors that govern NPY signal recognition and transduction, and would enable development of selective drugs.

N-Terminus to Arginine Side-Chain Cyclization of Linear Peptidic Neuropeptide Y Y4 Receptor Ligands Results in Picomolar Binding Constants

The family of neuropeptide Y (NPY) receptors comprises four subtypes (Y₁R, Y₂R, Y₄R, Y₅R), which are addressed by at least three endogenous peptides, i.e., NPY, peptide YY, and pancreatic polypeptide (PP), the latter showing a preference for Y₄R. A series of cyclic oligopeptidic Y₄R ligands were prepared by applying a novel approach, i.e., N-terminus to arginine side-chain cyclization. Most peptides acted as Y₄R partial agonists, showing up to 60-fold higher Y₄R affinity compared to the linear precursor peptides. Two cyclic hexapeptides (18, 24) showed higher Y₄R potency (Ca²⁺ aequorin assay) and, with pK_i values >10, also higher Y₄R affinity compared to human pancreatic polypeptide (hPP). Compounds such as 18 and 24, exhibiting considerably lower molecular weight and considerably more pronounced Y₄R selectivity than PP and previously described dimeric peptidic ligands with high Y₄R affinity, represent promising leads for the preparation of labeled tool compounds and might support the development of drug-like Y₄R ligands.

Structural Perspective on Ancient Neuropeptide Y-like System reveals Hallmark Features for Peptide Recognition and Receptor Activation

The neuropeptide Y (NPY) family is a peptide-activated G protein-coupled receptor system conserved across all bilaterians, and is involved in food intake, learning, and behavior. We hypothesized that comparing the NPY system in evolutionarily ancient organisms can reveal structural determinants of peptide recognition and receptor activation conserved in evolution. To test this hypothesis, we investigated the homologous FLP/NPR system of the protostome C.elegans. For three prototypic peptide-receptor complexes representing different ligand types, we integrate extensive functional data into structural models of the receptors. Common features include acidic patches in the extracellular loops (ECLs) of the receptors that cooperatively 'draw' the peptide into the binding pocket, which was functionally validated in vivo. A structurally conserved glutamate in the ECL2 anchors the peptides by a conserved salt bridge to the arginine of the RFamide motif. Beyond this conserved interaction, peptide binding show variability enabled by receptor-specific interactions. The family-conserved residue Q^3.32 is a key player for peptide binding and receptor activation. Altered interaction patterns at Q^3.32 may drastically increase the efficacy to activate the receptor.

Identification of a Suitable Peptidic Molecular Platform for the Development of NPY(Y1 )R-Specific Imaging Agents

NPY(Y1 )R (neuropeptide Y receptor subtype 1) is an important target structure for tumor-specific imaging and therapy as this receptor subtype is overexpressed in very high density and incidence especially in human breast cancer. Targeting this receptor with radiolabeled truncated analogues of the endogenous ligand NPY (neuropeptide Y) has, however, not yet resulted in satisfactory imaging results when using positron emission tomography (PET). This can be attributed to the limited stability of these PET imaging agents caused by their fast proteolytic degradation. Although highly promising NPY analogues were developed, their stability has only been investigated in very few cases. In this systematical work, we comparatively determined the stability of the five most promising truncated analogues of NPY that were developed over the last years, showing the highest receptor affinities and subtype selectivities. The stability of the peptides was assessed in human serum as well as in a human liver microsomal stability assay; these gave complementary results, thus demonstrating the necessity to perform both assays and not just conventional serum stability testing. Of the tested peptides, only [Lys(lauroyl)27 ,Pro30 ,Lys(DOTA)31 ,Bip32 ,Leu34 ]NPY27-36 showed high stability against peptidase degradation; thus this is the best-suited truncated NPY analogue for the development of NPY(Y1 )R-specific imaging agents.

Activation of NPY receptor subtype 1 by [D-His26]NPY is sufficient to prevent development of anxiety and depressive like effects in the single prolonged stress rodent model of PTSD

The neuropeptide Y (NPY) system plays an important role in mediating resilience to the harmful effect of stress in post-traumatic stress disorder (PTSD). It can mediate its effects via several G-protein coupled receptors: Y1R, Y2R, Y4R and Y5R. To investigate the role of individual NPY receptors in the resilience effects of NPY to traumatic stress, intranasal infusion of either Y1R agonists [D-His²⁶]NPY, [Leu³¹Pro³⁴]NPY, Y2R agonist NPY (3-36) or NPY were administered to male Sprague-Dawley rats immediately following the last stressor of the single prolonged stress (SPS) protocol, a widely used PTSD animal model. After 7 or 14 days, effects of the treatments were measured on the elevated plus maze (EPM) for anxiety, in forced swim test (FST) for development of depressive-like or re-experiencing behavior, in social interaction (SI) test for impaired social behavior, and acoustic startle response (ASR) for hyperarousal. [D-His²⁶]NPY, but not [Leu³¹Pro³⁴]NPY nor NPY (3-36) Y2R, was effective in preventing the SPS-elicited development of anxiety. Y1R, but not Y2R agonists prevented development of depressive- feature on FST, with [D-His²⁶]NPY superior to NPY. The results demonstrate that [D-His²⁶]NPY was sufficient to prevent development of anxiety, social impairment and depressive symptoms, and has promise as an early intervention therapy following traumatic stress.

Structural basis of ligand binding modes at the neuropeptide Y Y1 receptor

Neuropeptide Y (NPY) receptors belong to the G protein-coupled receptor (GPCR) superfamily and play important roles in food intake, anxiety and cancer regulation^1,2. The NPY/Y receptor system has emerged as one of the most complex networks with three peptide ligands (NPY, peptide YY and pancreatic polypeptide) binding to four receptors in mammals, namely Y₁, Y₂, Y₄ and Y₅ receptors, with different affinity and selectivity³. NPY is the most powerful stimulant of food intake and this effect is primarily mediated by Y₁ receptor (Y₁R)⁴. A number of peptides and small-molecule compounds have been characterized as Y₁R antagonists and have shown clinical potential in the treatment of obesity⁴, tumor¹ and bone loss⁵. However, their clinical usage has been hampered by low potency and selectivity, poor brain penetration ability or lack of oral bioavailability⁶. Here we report crystal structures of the human Y₁R bound to two selective antagonists UR-MK299 and BMS-193885 at 2.7 and 3.0 Å resolution, respectively. The structures combined with mutagenesis studies reveal binding modes of Y₁R to several structurally diverse antagonists and determinants of ligand selectivity. The Y₁R structure and molecular docking of the endogenous agonist NPY, together with nuclear magnetic resonance (NMR), photo-crosslinking and functional studies, provide insights into the binding behavior of the agonist and for the first time determine the interaction of its N terminus with the receptor. These insights into Y₁R can enable structure-based drug discovery targeting NPY receptors.

Unwinding of the C-Terminal Residues of Neuropeptide Y is critical for Y₂ Receptor Binding and Activation

Despite recent breakthroughs in the structural characterization of G-protein-coupled receptors (GPCRs), there is only sparse data on how GPCRs recognize larger peptide ligands. NMR spectroscopy, molecular modeling, and double-cycle mutagenesis studies were integrated to obtain a structural model of the peptide hormone neuropeptide Y (NPY) bound to its human G-protein-coupled Y2 receptor (Y2R). Solid-state NMR measurements of specific isotope-labeled NPY in complex with in vitro folded Y2R reconstituted into phospholipid bicelles provided the bioactive structure of the peptide. Guided by solution NMR experiments, it could be shown that the ligand is tethered to the second extracellular loop by hydrophobic contacts. The C-terminal α-helix of NPY, which is formed in a membrane environment in the absence of the receptor, is unwound starting at T(32) to provide optimal contacts in a deep binding pocket within the transmembrane bundle of the Y2R.

Neuropeptide Y receptors: how to get subtype selectivity

The neuropeptide Y (NPY) system is a multireceptor/multiligand system consisting of four receptors in humans (hY(1), hY(2), hY(4), hY(5)) and three agonists (NPY, PYY, PP) that activate these receptors with different potency. The relevance of this system in diseases like obesity or cancer, and the different role that each receptor plays influencing different biological processes makes this system suitable for the design of subtype selectivity studies. In this review we focus on the latest findings within the NPY system, we summarize recent mutagenesis studies, structure activity relationship studies, receptor chimera, and selective ligands focusing also on the binding mode of the native agonists.

Analogs of pancreatic polypeptide and peptide YY with a locked PP-fold structure are biologically active

Pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY), members of the PP-fold family share a high degree of sequence homology. Nuclear magnetic resonance (NMR) and X-ray crystallography studies have shown these peptides can adopt a tightly organized tertiary structure called the PP-fold, which has long been assumed to be the active structure of this family of peptides. To date, however, no studies have been completed with PYY and PP which confirm if the PP-fold structure is important for their physiological actions. The aim of the study was to test if PYY and PP locked into the PP-fold maintained biological activity. Therefore, we designed and produced analogs of PP and PYY in a cyclic conformation with two cysteine amino acid substitutions at the N-terminus and at position 27. These were oxidized to form a cysteine disulfide bond locking the peptides into the PP-fold structure. Studies demonstrate that the cyclic analogs have both similar in vivo activity to their parent molecules, and affinity for the Y2 and Y4 receptors. Results suggest that the proposed PP and PYY-fold is likely to be their biologically active conformation.

Are Hormones from the Neuropeptide Y Family Recognized by Their Receptors from the Membrane-Bound State?

Hormones and many other neurotransmitters, growth factors, odorant molecules, and light all present stimuli for a class of membrane-anchored receptors called G protein-coupled receptors (GPCRs). The GPCRs are the largest family of cell-surface receptors involved in signal transduction. About 1% of all known genes of Drosophila and more than 5% of the genes of Caenorhabditis elegans encode GPCRs. In addition, more than 50% of current therapeutic agents on the market target these receptors. When the enormous biological and pharmaceutical importance of these receptors is considered, it is surprising how little is known about the mechanism with which these receptors recognize their natural ligands. In this review we present a structural approach, utilizing techniques of high-resolution NMR spectroscopy, to address the question of whether peptides from the neuropeptide Y family of neurohormones are recognized directly from solution or from the membrane-bound state. In our studies we discovered that the structures of the membrane-bound species are better correlated to the pharmacological properties of these peptides than the solution structures are. These findings are supported by the observation that many biophysical properties of these peptides seem to be optimized for membrane binding. We finally present a scenario of possible events during receptor recognition.

Ala31-Aib32: identification of the key motif for high affinity and selectivity of neuropeptide Y at the Y5-receptor

The turn-inducing sequence Ala-Aib introduced into positions 31 and 32 of neuropeptide Y (NPY) and its analogues has been identified as the key structure for Y(5)-receptor selectivity. Analogues of NPY and PP/NPY chimera containing the motif Ala-Aib were prepared; these peptides turned out to be selective for the Y(5)-receptor. The affinity of the NPY-based peptides was in the range of 6-150 nM, while the affinity of three (Ala-Aib)-containing PP/NPY chimera was in the range of 0.2-0.9 nM. The circular dichroism spectra of the Aib analogues in aqueous solution were all characteristic of an alpha helix; however, they had different intensities of the two negative bands at 220 and 208 nm. Affinity and selectivity for the Y(5)-receptor were correlated with the ratio of the ellipticity at 220 nm versus the one at 208 nm (R), which indicates the presence of a pronounced helix (R > 1) versus a less stabile one (R < 1). When R was in the range 0.74-0.96, the affinity at the Y(5)-receptor was in the range >5 nM, while there was complete loss of affinity at the Y(4)-receptor. R > 1.15 was associated with very high affinity at the Y(5)-receptor and weak affinity at the Y(4)-receptor. These results suggest that the selectivity of the Ala(31)-Aib(32) motif for the Y(5)-receptor derives from a specific conformation that must be correlated with the bioactive conformation of NPY at this subtype.

Novel analogues of neuropeptide Y with a preference for the Y1-receptor

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian brain and acts in humans via at least three receptor subtypes: Y1, Y2, and Y5. Whereas selective agonists and antagonists are known for the Y2- and Y5-receptors, the Y1-receptor still lacks a highly selective agonist. This work presents the first NPY-based analogues with Y1-receptor preference and agonistic properties. Furthermore, the importance of specific amino acids of NPY for binding to the Y-receptor subtypes is presented. Amongst the analogues tested, [Phe7,Pro34]pNPY (where pNPY is porcine neuropeptide Y) showed the most significant Y1-receptor preference (> 1 : 3000-fold), with subnanomolar affinity to the Y1-receptor, and Ki values of approximately 30 nM for the Y2- and Y5-subtype, respectively. Variations of position 6, especially [Arg6,Pro34]pNPY and variations within positions 20-23 of NPY were found to result in further analogues with significant Y1-receptor preference (1 : 400-1 : 2000). In contrast, cyclo S-S [Cys20,Cys24]pNPY was found to be a highly selective ligand at the Y2-receptor, binding only threefold less efficiently than NPY. Analogues containing variations of positions 31 and 32 showed highly reduced affinity to the Y1-receptor, while binding to the Y5-receptor was affected less. Inhibition of cAMP-accumulation of selected peptides with replacements within position 20-23 of NPY showed preserved agonistic properties. The NPY analogues tested give insights into ligand-receptor interaction of NPY at the Y1-, Y2- and Y5-receptor and contribute to our understanding of subtype selectivity. Furthermore, the Y1-receptor-preferring peptides are novel tools that will provide insight into the physiological role of the Y1-receptor.

Structure and dynamics of micelle-bound neuropeptide Y: comparison with unligated NPY and implications for receptor selection

The biological importance of the neuropeptide Y (NPY) has steered a number of investigations about its solution structure over the last 20 years. Here, we focus on the comparison of the structure and dynamics of NPY free in solution to when bound to a membrane mimetic, dodecylphosphocholine (DPC) micelles, as studied by 2D (1)H NMR spectroscopy. Both, free in solution and in the micelle-bound form, the N-terminal segment (Tyr1-Glu15) is shown to extend like a flexible tail in solution. This is not compatible with the PP-fold model for NPY that postulates backfolding of the flexible N terminus onto the C-terminal helix. The correlation time (tau(c)) of NPY in aqueous solution, 5.5 (+/-1.0) ns at 32 degrees C, is only consistent with its existence in a dimeric form. Exchange contributions especially enhancing transverse relaxation rates (R(2)) of residues located on one side of the C-terminal helix of the molecule are supposed to originate from dimerization of the NPY molecule. The dimerization interface was directly probed by looking at (15)N-labeled NPY/spin-labeled [TOAC34]-[(14)N]-NPY heterodimers and revealed both parallel and anti-parallel alignment of the helices. The NMR-derived three-dimensional structure of micelle-bound NPY at 37 degrees C and pH 6.0 is similar but not identical to that free in solution. The final set of 17 lowest-energy DYANA structures is particularly well defined in the region of residues 21-31, with a mean pairwise RMSD of 0.23 A for the backbone heavy atoms and 0.85 A for all heavy atoms. The combination of NMR relaxation data and CD measurements clearly demonstrates that the alpha-helical region Ala18-Thr32 is more stable, and the C-terminal tetrapeptide becomes structured only in the presence of the phosphocholine micelles. The position of NPY relative to the DPC micelle surface was probed by adding micelle integrating spin labels. Together with information from (1)H,(2)H exchange rates, we conclude that the interaction of NPY with the micelle is promoted by the amphiphilic alpha-helical segment of residues Tyr21-Thr32. NPY is located at the lipid-water interface with its C-terminal helix parallel to the membrane surface and penetrates the hydrophobic interior only via insertions of a few long aliphatic or aromatic side-chains. From these data we can demonstrate that the dimer interface of neuropeptide Y is similar to the interface of the monomer binding to DPC-micelles. We speculate that binding of the NPY monomer to the membrane is an essential key step preceeding receptor binding, thereby pre-orientating the C-terminal tetrapeptide and possibly inducing the bio-active conformation.

Molecular characterization of the ligand-receptor interaction of the neuropeptide Y family

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) belong to the NPY hormone family and activate a class of receptors called the Y-receptors, and also belong to the large superfamily of the G-protein coupled receptors. Structure-affinity and structure-activity relationship studies of peptide analogs, combined with studies based on site-directed mutagenesis and anti-receptor antibodies, have given insight into the individual characterization of each receptor subtype relative to its interaction with the ligand, as well as to its biological function. A number of selective antagonists at the Y1-receptor are available whose structures resemble that of the C-terminus of NPY. Some of these compounds, like BIBP3226, BIBO3304 and GW1229, have recently been used for in vivo investigations of the NPY-induced increase in food intake. Y2-receptor selective agonists are the analog cyclo-(28/32)-Ac-[Lys28-Glu32]-(25-36)-pNPY and the TASP molecule containing two units of the NPY segment 21-36. Now the first antagonist with nanomolar affinity for the Y2-receptor is also known, BIIE0246. So far, the native peptide PP has been shown to be the most potent ligand at the Y4-receptor. However, by the design of PP/NPY chimera, some analogs have been found that bind not only to the Y4-, but also to the Y5-receptor with subnanomolar affinities, and are as potent as NPY at the Y1-receptor. For the characterization of the Y5-receptor in vitro and in vivo, a new class of highly selective agonists is now available. This consists of analogs of NPY and of PP/NPY chimera which all contain the motif Ala31-Aib32. This motif has been shown to induce a 3(10)-helical turn in the region 28-31 of NPY and is suggested to be the key motif for high Y5-receptor selectivity. The results of feeding experiments in rats treated with the first highly specific Y5-receptor agonists support the hypothesis that this receptor plays a role in the NPY-induced stimulation of food intake. In conclusion, the selective compounds for the different Y receptor subtypes known so far are promising tools for a better understanding of the physiological properties of the hormones of the NPY family and related receptors.

BIBP 3226, the first selective neuropeptide Y1 receptor antagonist: a review of its pharmacological properties

Based on the assumption that the pharmacophoric groups interacting with the Y1 receptor are located in the C-terminal part of neuropeptide Y, low molecular weight compounds with high affinity and selectivity for the Y1 receptor were designed and synthesized. The prototype BIBP 3226 possesses affinity for the Y1 receptor in the nanomolar range. In addition, this compound is selective displaying rather low affinity for Y2, Y3, Y4 and a set of 60 other receptors. Both biochemical and pharmacological studies showed that BIBP 3226 behaves as a competitive antagonist. Using BIBP 3226 it was possible to investigate the role of NPY and/or Y1 receptors in blood pressure regulation. The interesting observation was that antagonism to Y1 receptors had no major influence on the basal blood pressure but attenuated stress induced hypertension. This strongly supports the hypothesis that NPY is mainly released during stress involving intense sympathetic nervous system activation. Moreover, BIBP 3226 can be used to characterize NPY receptor subtypes. For instance, we were able to show that presynaptic NPY receptors mediating catecholamine release do not solely belong to the Y2 subtype, but that presynaptic Y1 receptors also exist. In conclusion, BIBP 3226 has been shown to be an important tool for the elucidation of the physiological role of Y1 receptors in the cardiovascular system.