The activity of prolactin releasing peptide correlates with its helicity

Search for lipidized PrRP analogs with strong anorexigenic effect: In vitro and in vivo studies

Prolactin-releasing peptide (PrRP) is an anorexigenic neuropeptide that attenuates food intake and increases energy expenditure. We designed three series of new lipidized PrRP31 analogs of different lengths of fatty acids attached at amino acids 1 or 11 directly or via linkers, part of them acetylated at the N-terminus and/or modified with dichlorophenylalanine (PheCl₂) at the C-terminus. We tested their affinity for and activation of signaling pathways relevant to receptors GPR10, NPFF-R2, and NPFF-R1, effect on food intake in fasted or freely fed mice and rats, and stability in rat plasma. We aimed to select a strong dual GPR10/NPFF-R2 agonist whose affinity for NPFF-1 was not enhanced. The selected potent analog was then tested for body weight-lowering potency after chronic administration in mice with diet-induced obesity. PrRP31 analogs lipidized by monocarboxylic fatty acids showed strong dual affinity for both GPR10 and NPFF-R2 and activated MAPK/ERK1/2, Akt and CREB in cells overexpressing GPR10 and NPFF-R2. The selected analog stabilized at N- and C-termini and palmitoylated through the TTDS linker to Lys¹¹ is a powerful dual agonist GPR10/NPFF-R2 at not enhanced affinity for NPFF-R1. It showed strong anti-obesity properties in mice with diet-induced obesity and became a potential compound for further studies.

The Structural Basis of Peptide Binding at Class A G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) represent the largest membrane protein family and a significant target class for therapeutics. Receptors from GPCRs’ largest class, class A, influence virtually every aspect of human physiology. About 45% of the members of this family endogenously bind flexible peptides or peptides segments within larger protein ligands. While many of these peptides have been structurally characterized in their solution state, the few studies of peptides in their receptor-bound state suggest that these peptides interact with a shared set of residues and undergo significant conformational changes. For the purpose of understanding binding dynamics and the development of peptidomimetic drug compounds, further studies should investigate the peptide ligands that are complexed to their cognate receptor.

Prolactin-Releasing Peptide: Physiological and Pharmacological Properties

Prolactin-releasing peptide (PrRP) belongs to the large RF-amide neuropeptide family with a conserved Arg-Phe-amide motif at the C-terminus. PrRP plays a main role in the regulation of food intake and energy expenditure. This review focuses not only on the physiological functions of PrRP, but also on its pharmacological properties and the actions of its G-protein coupled receptor, GPR10. Special attention is paid to structure-activity relationship studies on PrRP and its analogs as well as to their effect on different physiological functions, mainly their anorexigenic and neuroprotective features and the regulation of the cardiovascular system, pain, and stress. Additionally, the therapeutic potential of this peptide and its analogs is explored.

Design of a Long-Acting and Selective MEG-Fatty Acid Stapled Prolactin-Releasing Peptide Analog

Anorexigenic peptides offer promise as potential therapies targeting the escalating global obesity epidemic. Prolactin-releasing peptide (PrRP), a novel member of the RFamide family secreted by the hypothalamus, shows therapeutic potential by decreasing food intake and body weight in rodent models via GPR10 activation. Here we describe the design of a long-acting PrRP using our recently developed novel multiple ethylene glycol-fatty acid (MEG-FA) stapling platform. By incorporating serum albumin binding fatty acids onto a covalent side chain staple, we have generated a series of MEG-FA stapled PrRP analogs with enhanced serum stability and in vivo half-life. Our lead compound 18-S4 exhibits good in vitro potency and selectivity against GPR10, improved serum stability, and extended in vivo half-life (7.8 h) in mouse. Furthermore, 18-S4 demonstrates a potent body weight reduction effect in a diet-induced obesity (DIO) mouse model, representing a promising long-acting PrRP analog for further evaluation in the chronic obesity setting.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Integrating solid-state NMR and computational modeling to investigate the structure and dynamics of membrane-associated ghrelin

The peptide hormone ghrelin activates the growth hormone secretagogue receptor 1a, also known as the ghrelin receptor. This 28-residue peptide is acylated at Ser3 and is the only peptide hormone in the human body that is lipid-modified by an octanoyl group. Little is known about the structure and dynamics of membrane-associated ghrelin. We carried out solid-state NMR studies of ghrelin in lipid vesicles, followed by computational modeling of the peptide using Rosetta. Isotropic chemical shift data of isotopically labeled ghrelin provide information about the peptide’s secondary structure. Spin diffusion experiments indicate that ghrelin binds to membranes via its lipidated Ser3. Further, Phe4, as well as electrostatics involving the peptide’s positively charged residues and lipid polar headgroups, contribute to the binding energy. Other than the lipid anchor, ghrelin is highly flexible and mobile at the membrane surface. This observation is supported by our predicted model ensemble, which is in good agreement with experimentally determined chemical shifts. In the final ensemble of models, residues 8–17 form an α-helix, while residues 21–23 and 26–27 often adopt a polyproline II helical conformation. These helices appear to assist the peptide in forming an amphipathic conformation so that it can bind to the membrane.

In vitro modification of substituted cysteines as tool to study receptor functionality and structure-activity relationships

Mutagenic investigations of expressed membrane proteins are routine, but the variety of modifications is limited by the twenty canonical amino acids. We describe an easy and effective cysteine substitution mutagenesis method to modify and investigate distinct amino acids in vitro. The approach combines the substituted cysteine accessibility method (SCAM) with a functional signal transduction readout system using different thiol-specific reagents. We applied this approach to the prolactin-releasing peptide receptor (PrRPR) to facilitate biochemical structure-activity relationship studies of eight crucial positions. Especially for D(6.59)C, the treatment with the positively charged methanethiosulfonate (MTS) ethylammonium led to an induced basal activity, whereas the coupling of the negatively charged MTS ethylsulfonate nearly reconstituted full activity, obviously by mimicking the wild-type charged side chain. At E(5.26)C, W(5.28)C, Y(5.38)C, and Q(7.35)C, accessibility was observed but hindered transfer into the active receptor conformation. Accordingly, the combination of SCAM and signaling assay is feasible and can be adapted to other G-protein-coupled receptors (GPCRs). This method circumvents the laborious way of inserting non-proteinogenic amino acids to investigate activity and ligand binding, with rising numbers of MTS reagents allowing selective side chain modification. This method pinpoints to residues being accessible but also presents potential molecular positions to investigate the global conformation.