Structure-based search for peptide ligands that cross-react with melanocortin receptors

Area of Science:

• Biochemistry
• Pharmacology
• Molecular Biology

Background:

• Melanocortin receptors (MCRs) are G-protein coupled receptors involved in various physiological processes.
• Identifying specific peptide ligands for MCRs is crucial for understanding their function and developing therapeutics.
• Previous research identified small peptide structures antagonizing amphibian MCRs.

Purpose of the Study:

• To define sequence motifs that can accurately identify peptide ligands targeting melanocortin receptors (MCRs).
• To investigate the potential of identified motifs in distinguishing MCR antagonists from ligands of other receptors.

Main Methods:

• Screening of combinatorial peptide libraries to identify initial MCR antagonists.
• Examining peptide-ligands containing identified motifs (e.g., D-Trp-AAx) for MCR antagonist activity.
• Testing compounds against amphibian and recombinant human MCRs, including analogs of known peptide families.

Main Results:

• Six of seven tested compounds with the D-Trp-AAx motif exhibited antagonist activity at the amphibian MCR.
• The anticancer peptide [Arg8, D-Trp7.9, N-methyl-Phe8]-substance P showed potent amphibian MCR antagonism (Kd 31 nM).
• Mu-opioid antagonist CTAP blocked the amphibian MCR, while its analog CTOP agonized it; CTAP also interacted with human MC1 receptor.

Conclusions:

• Dipeptide motifs, specifically D-Trp-AAx, were identified that distinguish amphibian MCR antagonist ligands.
• This motif-based identification approach may be applicable to other receptors and their subtypes.
• Cross-reactivity of opioid receptor analogs (CTAP, CTOP) with MCRs necessitates careful consideration in drug development.