The Melanocortin System: Structure Activity Relationships of Alpha-N-Methylated MT-II Analogues and Mutation Studies of Human Melanocortin Receptor Subtypes 1 and 4
AuthorDedek, Matthew Milan
Keywordsstructure activity relationship
melanocortin 1 receptor
melanocortin 4 receptor
AdvisorHruby, Victor J.
Committee ChairHruby, Victor J.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe melanocortin system regulates various physiological processes including feeding behavior, sexual function, skin pigmentation and photoprotection via five G-protein coupled receptors and several endogenous ligands. There is a need for selective and potent ligands to the human melanocortin receptors (hMCRs) that can chemically resolve these various functions. This thesis presents three studies aimed at refining the understanding of the structural differences between binding pockets of the hMCR subtypes. In the first study α-N-methylated analogues of the non-selective agonist, MT-II, are evaluated for their in vitro function. This study produced the most potent hMC1R selective agonist to date. The following two studies examine the effects of mutations on the biological activity of melanocortin receptor subtypes 1 and 4. Much of the mutation study data is preliminary and requires a demonstration of reproducibility.
Degree ProgramMedical Pharmacology
Degree GrantorUniversity of Arizona
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Synthesis of Novel Amino Acids and Use of Peptides & Peptidomimetics Containing Unnatural Amino Acids for the Development of Selective Melanocortin Peptide Antagonists and for the Study of Melanocortin Receptor SignalingHruby, Victor J; Qu, Hongchang; Mash, Eugene A.; Pyun, Jeffrey; Walker, F. Ann (The University of Arizona., 2007)Unnatural amino acids are indispensible tools, not only for the elucidation of molecular mechanisms during the study of the complicated biological system, but also for the development of novel peptide and protein drugs with better efficacy and lower toxicity. Beta-substituted gamma,delta-unsaturated amino acids have been shown to be an important type of novel amino acid because of the terminal double bond which can be converted to many other functionalities. The methodology for the synthesis of syn-beta-substituted gamma,delta-unsaturated amino acids has been developed. However, there is no satisfactory general method for the synthesis of anti-beta-substituted gamma,delta-unsaturated amino acids. Therefore, a general methodology was developed by using the Eschenmoser-Claisen rearrangement for the synthesis of both racemic and optically active anti-beta-substituted gamma,delta-unsaturated amino acids. This rearrangement is highly diastereoselective and good asymmetric induction was obtained with a relatively small C2-symmetric chiral auxiliary (2R,5R)-dimethylpyrrolidine. In an effort to design peptide antagonists that are selective for human melanocortin 4 receptor, highly constrained trans and cis 4-guanidinium proline derivatives were synthesized and incorporated in various melanotropin analogues designed to mimic the endogenous hMC1,4R selective antagonist hASIP (Agouti Signaling Protein) central loop. Biological assays show that some of these analogues are highly selective for hMC1R and/or hMC4R with partial agonist or antagonist activities due to a new beta-turn structure induced by the presence of the constrained amino acids. According to molecular modeling studies, the lowest energy conformations of these selective analogues resemble the NMR solution structure of the hASIP central loop. Therefore, a new template was developed for the rational design of novel selective melanotropin analogues that may have therapeutic potential. To further understand the molecular mechanisms of hMC4R signaling upon agonist activation, an hMC4R selective nonpeptide agonist THIQ and its fluorescent dye labeled derivatives were needed to compare to peptide agonist MTII with regard to receptor phosphorylation, internalization, etc. An improved synthetic method was developed for the efficient synthesis of THIQ. A method for the synthesis of TRITC labeled THIQ derivatives was also developed.
Developing Melanocortin 3 Selective Ligands through C-Terminal Modification of Melanocortin PeptidesHruby, Victor J.; Nyberg, Joel Benjamin; Ghosh, Indraneel; Jewett, John; Mash, Eugene; Brown, Michael; Hruby, Victor J. (The University of Arizona., 2013)The melanocortin 3 and 4 receptors share 58% overall amino acid identity and 76% similarity. This high level of similarity between the MC3R and the MC4R underscores the difficulties associated with developing MC3R selective ligands, and as a consequence little is known of the physiological functions of the melanocortin 3 receptor. Previous research showing the differences between endogenous non-selective ligands and melanocortin 3 receptor selective ligands are mainly within the C-terminus of the melanocortin peptide. These findings have been exploited in this research using known melanocortin 3 and 4 selective ligands modified at their respective C-termini to develop some very promising melancortin 3 selective antagonists and agonists, analog 5 ([CO(CH₂)₂CO-DNal(2')-Arg-Trp-Lys]-Gly-Lys-Pro-Val-NH₂) and analog 20 ((H-DNal(2')-c[Asp-Pr6-DPhe-Arg-Trp-Lys]-Ala-Gly-Pro-Val-NH₂) respectively. Additional studies using molecular modeling have produced further insights into the structural basis for selectivity. Finally, we have been developing a new scaffold for the melanocortin receptor using cyclic dipeptide derivatives.
Theoretical Study of Selective Human Melanocortin Receptors Agonists and AntagonistsSchwartz, Steven; Ng, Yvonne (The University of Arizona., 2015)G-Protein Couple Receptors represent possibly the most important target class of proteins for drug discovery. GPCRs include many subcategories and this study focuses on melanocortin receptors. The experimentally determined NMR structures of two cyclic peptides analogues: SHU9119 (Ac-Nle-c[Asp-His-D-Nal(2')-Arg-Trp-Lys]-NH₂), and MT-II (Ac-Nle-c[Asp- His-Phe-Arg-Trp-Lys]-NH₂) have been determined. We found that MTII is a potent and selective agonist for hMC4R and hMC3R but antagonist for hMC1R and hMCR5, whereas SHU-9119 is a better agonist for hMC1R and hMC5R but antagonist for hMC4R and hMC3R. These results are consistent with the experimental data. Another part of the study describes the interactions between each ligand and receptor. Arg⁶ of the ligands was found to have the most interactions with every receptor which suggests that is critical important for binding. The active site residues D121 and D117 of hMCR1 had the most interactions with both ligands. In hMC3R, D121 and D117 interacted the most with MT-II and SHU9119. In hMC4R, residue D122 had more interaction with MT-II than SHU9119, In hMC5R, the residue D119 interacted the most with either MT-II or SHU9119, whereas. Residue W251 interacted with SHU9119 only. Also, residues F254 interacted more with MT-II than in SHU9119.