Design and synthesis of peptidic partial agonists of human neuromedin U receptor 1 with enhanced serum stability

Discovery of a Pentapeptide Antagonist to Human Neuromedin U Receptor 1

Neuromedin U (NMU) activates two types of receptors (NMUR1 and NMUR2), and the former is mainly expressed in the peripheral tissues, including the intestinal tract and lung tissues. Since NMUR1 contributes to the promotion of type 2 inflammation in these tissues, it is a potential target to suppress inflammatory responses. However, promising antagonist candidates for human NMUR1 have not yet been developed. Here we successfully identified pentapeptide antagonist 9a through a structure-activity relationship study based on hexapeptide lead 1. Its antagonistic activity against human NMUR1 was 10 times greater than that against NMUR2. This is a breakthrough in the development of NMUR1-selective antagonists. Although 9a was relatively stable in the plasma, the C-terminal amide was rapidly degraded to the carboxylic acid by the serum endopeptidase thrombin, which acted as an amidase. This basic information would aid in sample handling in future biological evaluations.

Peptide Tool-Driven Functional Elucidation of Biomolecules Related to Endocrine System and Metabolism

The enhancement of basic research based on biomolecule-derived peptides has the potential to elucidate their biological function and lead to the development of new drugs. In this review, two biomolecules, namely "neuromedin U (NMU)" and "myostatin," are discussed. NMU, a neuropeptide first isolated from the porcine spinal cord, non-selectively activates two types of receptors (NMUR1 and NMUR2) and displays a variety of physiological actions, including appetite suppression. The development of receptor-selective regulators helps elucidate each receptor's detailed biological roles. A structure-activity relationship (SAR) study was conducted to achieve this purpose using the amidated C-terminal core structure of NMU for receptor activation. Through obtaining receptor-selective hexapeptide agonists, molecular functions of the core structure were clarified. Myostatin is a negative regulator of skeletal muscle growth and has attracted attention as a target for treating atrophic muscle disorders. Although the protein inhibitors, such as antibodies and receptor-decoys have been developed, the inhibition by smaller molecules, including peptides, is less advanced. Focusing on the inactivation mechanism by prodomain proteins derived from myostatin-precursor, a first mid-sized α-helical myostatin-inhibitory peptide (23-mer) was identified from the mouse sequence. The detailed SAR study based on this peptide afforded the structural requirements for effective inhibition. The subsequent computer simulation proposed the docking mode at the activin type I receptor binding site of myostatin. The resulting development of potent inhibitors suggested the existence of a more appropriate binding mode linked to their β-sheet forming properties, suggesting that further investigations might be needed.

Structural insights into the peptide selectivity and activation of human neuromedin U receptors

Neuromedin U receptors (NMURs), including NMUR1 and NMUR2, are a group of G_q/11-coupled G protein-coupled receptors (GPCRs). NMUR1 and NMUR2 play distinct, pleiotropic physiological functions in peripheral tissues and in the central nervous system (CNS), respectively, according to their distinct tissue distributions. These receptors are stimulated by two endogenous neuropeptides, neuromedin U and S (NMU and NMS) with similar binding affinities. NMURs have gathered attention as potential drug targets for obesity and inflammatory disorders. Specifically, selective agonists for NMUR2 in peripheral tissue show promising long-term anti-obesity effects with fewer CNS-related side effects. However, the mechanisms of peptide binding specificity and receptor activation remain elusive. Here, we report four cryo-electron microscopy structures of G_q chimera-coupled NMUR1 and NMUR2 in complexes with NMU and NMS. These structures reveal the conserved overall peptide-binding mode and the mechanism of peptide selectivity for specific NMURs, as well as the common activation mechanism of the NMUR subfamily. Together, these findings provide insights into the molecular basis of the peptide recognition and offer an opportunity for the design of the selective drugs targeting NMURs.

Neuromedin U receptors (NMURs) are potential drug targets for obesity and inflammatory disorders. Here, the authors report structural basis for neuromedin recognition and activation mechanism of NMURs.