A fragment of the Escherichia coli ClpB heat-shock protein is a micromolar melanocortin 1 receptor agonist

Abstract

The melanocortin system consists of five receptor subtypes (MC1-5R), endogenous agonists derived from the proopiomelanocortin gene transcript, and the antagonists agouti and agouti-related protein. The Escherichia coli heat shock protein ClpB has previously been described as an antigen mimetic to the endogenous melanocortin agonist α-MSH. Herein, we investigated if a fragment of the ClpB protein could directly signal through the melanocortin receptors. We synthesized a complementary fragment of the ClpB protein that partially aligned with α-MSH. Pharmacological assessment of this fragment resulted in no antagonist activity at the MC3R or the MC4R and no agonist activity at the MC4R. Partial receptor activation was observed for the MC3R and MC5R at 100 μM concentrations. This fragment was shown to be a full micromolar MC1R agonist and may serve as a template for future research into selective MC1R ligands.

Structure–Activity Relationship Studies on a Macrocyclic Agouti-Related Protein (AGRP) Scaffold Reveal Agouti Signaling Protein (ASP) Residue Substitutions Maintain Melanocortin-4 Receptor Antagonist Potency and Result in Inverse Agonist Pharmacology at the Melanocortin-5 Receptor

“…58–60 The MC2R is only stimulated by ACTH and was therefore excluded from this study. Compounds were first assayed for agonist activity at the MCRs; ligands that did not possess full agonist activity at the MC3R and MC4R were then assayed for antagonist activity using a Schild paradigm 61 and NDP-MSH as the agonist.…”

“…Since the AlphaScreen assay is a competition assay (higher concentrations of ligand result in lower signal), concentration-activity curves were normalized to baseline and maximal NDP-MSH signal for illustrative purposes as previously described. 58,59 Due to the inherent error associated with the assay in our laboratory, compounds that were within a 3-fold potency range were considered equipotent.…”

A Direct in Vivo Comparison of the Melanocortin Monovalent Agonist Ac-His-DPhe-Arg-Trp-NH2 versus the Bivalent Agonist Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH2: A Bivalent Advantage

“…The EC 50 values for ligands NDP-MSH, α-MSH, MTII, CJL-1-87, and CJL-1-14 at the singly expressed mMC3R and mMC4R were consistent with the field. 21, 114, 115 …”

A Macrocyclic Agouti-Related Protein/[Nle4,DPhe7]α-Melanocyte Stimulating Hormone Chimeric Scaffold Produces Subnanomolar Melanocortin Receptor Ligands

“…42–44 The MC2R is only stimulated by ACTH and was therefore excluded from this study. The potent, nonselective melanocortin ligand NDP-MSH was used as a positive control; 45 the nonselective melanocortin agonists MTII and HfRW are included for reference.…”