Evidence for diversity in the activation of the melanocortin 2 receptor: A study on gar, elephant shark and stingray MC2Rs

• Published in: Peptides (New York, N.Y. : 1980) Vol. 124; p. 170209
• Main Authors: Hoglin, Brianne E., Ferguson, Amanda, Pahlavan, Sheila, Dores, Robert M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2020
• Subjects: Adrenocorticotropic Hormone - metabolism; Adrenocorticotropic Hormone - pharmacology; Alanine - genetics; Amino Acid Substitution; Animals; Binding Sites; CHO Cells; Cricetulus; Elephant shark; Evolution; Evolution, Molecular; Fish Proteins - genetics; Fish Proteins - metabolism; Fishes; Melanocortin receptors; MRAP1; MRAP2; Peptide Fragments - metabolism; Peptide Fragments - pharmacology; Protein Interaction Domains and Motifs; Receptor, Melanocortin, Type 2 - genetics; Receptor, Melanocortin, Type 2 - metabolism; Red stingray; Sharks; Skates, Fish; Species Specificity; Spotted gar; Spotted gar; Melanocortin receptors; Evolution; Elephant shark; Red stingray; MRAP2; MRAP1
• ISSN: 0196-9781; 1873-5169
• DOI: 10.1016/j.peptides.2019.170209

•MC2R is unique among the MCR family with its ligand selectivity for ACTH alone.•For bony vertebrate MC2Rs, two motifs in ACTH are required for activation.•Cartilaginous fish MC2R orthologs defy the expected ligand selectivity.•This study suggests a one-step activation mechanism for elephant shark MC2R.•A two-step activation mechanism is predicted for stingray and gar MC2R. The melanocortin-2 receptor (MC2R) is a critical component of the HPI and HPA axes of cartilaginous fishes, teleosts and tetrapods. Studies on teleost and tetrapod orthologs suggest two contact sites between ACTH and the receptor involving the following motifs on ACTH: H6F7R8W9 and K15K16R17R18P19. Using spotted gar (g) MC2R as a representative bony fish MC2R ortholog, we found that activation of gMC2R in Chinese Hamster Ovary (CHO) cells was diminished following stimulation of the transfected cells with hACTH(1–24) analogs substituted with alanine at either the H6F7R8W9 or K15K16R17R18P19 motifs compared to stimulation with hACTH(1–24). This observation suggests two ligand contact sites necessary for activation of the gMC2R. The same experiments were done with elephant shark (es) MC2R, however only the H6F7R8W9 analogs blocked activation, pointing to a single contact on esMC2R. Conversely, the red stingray (sr) MC2R activation was blocked by both the H6F7R8W9 and K15K16R17R18P19 alanine-substituted analogs. Together these results build a picture of the evolution of the ligand and receptor interaction between ACTH and MC2R orthologs of different taxa. These results will be discussed in light of the parallel evolution of MC2R orthologs in cartilaginous fishes and bony vertebrates.