Characterization of Melanocortin NDP-MSH Agonist Peptide Fragments at the Mouse Central and Peripheral Melanocortin Receptors

Abstract

The central melanocortin receptors, melanocortin-4 (MC4R) and melanocortin-3 (MC3R), are involved in the regulation of satiety and energy homeostasis. The MC4R in particular has become a pharmaceutical industry drug target due to its direct involvement in the regulation of food intake and its potential therapeutic application for the treatment of obesity-related diseases. The melanocortin receptors are stimulated by the native ligand, alpha-melanocyte stimulating hormone (alpha-MSH). The potent and enzymatically stable analogue NDP-MSH (Ac-Ser-Tyr-Ser-Nle-Glu-His-DPhe-Arg-Trp-Gly-Lys-Pro-Val-NH(2)) is a lead peptide for the identification of melanocortin amino acids important for receptor molecular recognition and stimulation. We have synthesized nine peptide fragments of NDP-MSH, deleting N- and C-terminal amino acids to determine the "minimally active" sequence of NDP-MSH. Additionally, five peptides were synthesized to study stereochemical inversion at the Phe 7 and Trp 9 positions in attempts to increase tetra- and tripeptide potencies. These peptide analogues were pharmacologically characterized at the mouse melanocortin MC1, MC3, MC4, and MC5 receptors. This study has identified the Ac-His-DPhe-Arg-Trp-NH(2) tetrapeptide as possessing 10 nM agonist activity at the brain MC4R. The tripeptide Ac-DPhe-Arg-Trp-NH(2) possessed micromolar agonist activities at the MC1R, MC4R, and MC5R but only slight stimulatory activity was observed at the MC3R (at up to 100 microM concentration). This study has also examined to importance of both N- and C-terminal NDP-MSH amino acids at the different melanocortin receptors, providing information for drug design and identification of putative ligand-receptor interactions.

Synthesis and Pharmacology of α/β3-Peptides Based on the Melanocortin Agonist Ac-His-dPhe-Arg-Trp-NH2 Sequence

“…2−4 The conserved tetrapeptide sequence has been determined to be important for the ligand binding/molecular recognition and stimulation of melanocortin receptors (MCRs). 5,6 The MCRs are G protein-coupled receptors (GPCRs) that activate the cyclic adenosine monophosphate (cAMP) signal transduction pathway and generate a cascade of intracellular events, which result in physiological responses. Five melanocortin receptors (MC1−5R) have been cloned and characterized.…”

“…6 The melanocortin agonist core peptide Ac-His-Phe-Arg-Trp-NH 2 (2), possessed 130-, 25-, 200-, and 18-fold decreased potency compared to 1 at the mMC1R and mMC3−5Rs, respectively. The tripeptide AcDPhe-Arg-Trp-NH 2 (3) possessed 550-fold decreased activity at the mMC1R compared to 1 and was only able to stimulate the mMC3R, mMC4R, and mMC5R at 40%, 70%, and 70% of the maximum cAMP response, respectively, at 100 μM concentrations.…”

Design, Synthesis, Structural and Functional Characterization of Novel Melanocortin Agonists Based on the Cyclotide Kalata B1

“…Substitution of Met 4 with norleucine (Nle) and modifying the conformation of Phe 7 to D-Phe in ␣-MSH (see Table 1) yielded a stable subnanomolar agonist named NDP-␣-MSH (20). Additionally, it has been shown that the His-D-Phe-Arg-Trp tetrapeptide alone has nanomolar activity on the MC4R (21). In another study, a truncated analogue of the inverse agonist agouti-related protein was turned into a full agonist by exchanging the binding sequence with His-D-Phe-ArgTrp (22).…”

β-Turn secondary structure and melanocortin ligands

“…Both α-MSH and ACTH, as well as the other endogenous melanocortin ligands, contain a core His-Phe-Arg-Trp sequence that has been postulated to be important for molecular recognition and receptor stimulation. [35][36][37][38][39] Molecular recognition of peptides by their cognate receptors has been attributed to the ligand pharmacophore, secondary structure, and chemical functionality of the amino acid side chains. One of the most common and important secondary structures found in peptide hormones that stimulate GPCRs is a reverse turn, specifically a β-turn.…”