title: Molecular interaction of Agouti protein and Agouti-related protein with human melanocortin receptors.
abstract: Agouti protein and the Agouti-related protein (AGRP) are antagonists of the melanocortin-3 receptor and melanocortin-4 receptor. Both proteins contain 10 cysteines in the C-terminal domain arranged in five disulfide bonds. One possible arrangement of the disulfide bonds predicts an octapeptide loop, and the chemical properties of four residues within this loop (residues 111-114 in human AGRP) bear striking resemblance to those of several melanocortin peptides, including alpha-MSH, MT-II, and SHU-9119. We showed that cyclic synthetic octapeptides based on the sequence of this loop from Agouti protein or human AGRP are functional antagonists of the human melanocortin-4 receptor. All peptides had a lower affinity for the melanocortin-3 receptor than for the melanocortin-4 receptor. Substitution of serines for cysteines resulted in linear peptides which had reduced binding affinities for both receptors. Mutational analysis of human AGRP indicated that its C-terminal domain is functionally equivalent to the intact human AGRP. The RFF111-113 triplet appears to be the most critical portion of AGRP in determining the binding affinity for both melanocortin-3 and melanocortin-4 receptors. These data strongly suggest that the loop defined by Cys-110 and Cys-117 is critical in determining the antagonist activity of human AGRP. Our data provide indirect evidence for the suggestion that the Cys-110 to Cys-117 octapeptide loop of human AGRP mimics the conformation of alpha-MSH, MT-II, and SHU-9119.
authors.affiliation: Department of Obesity Research, Merck Research Laboratories, Rahway, New Jersey 07065, USA. mike_tota@merck.com
authors.forename: M R
authors.initials: MR
authors.lastname: Tota
authors.forename: T S
authors.initials: TS
authors.lastname: Smith
authors.forename: C
authors.initials: C
authors.lastname: Mao
authors.forename: T
authors.initials: T
authors.lastname: MacNeil
authors.forename: R T
authors.initials: RT
authors.lastname: Mosley
authors.forename: L H
authors.initials: LH
authors.lastname: Van der Ploeg
authors.forename: T M
authors.initials: TM
authors.lastname: Fong
mesh_terms: D054366:Agouti Signaling Protein; D054369:Agouti-Related Protein; D000595:Amino Acid Sequence; D000818:Animals; D004252:DNA Mutational Analysis; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011506:Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D044105:Receptor, Melanocortin, Type 4; D018000:Receptors, Peptide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D000521:alpha-MSH / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: C515198:AGRP protein, human; C515182:ASIP protein, human; D054366:Agouti Signaling Protein; D054369:Agouti-Related Protein; C515199:Agrp protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D009842:Oligopeptides; D010456:Peptides, Cyclic; D011506:Proteins; D044105:Receptor, Melanocortin, Type 4; D018000:Receptors, Peptide; C515183:a protein, mouse; D000521:alpha-MSH; C027756:MSH, 4-Nle-7-Phe-alpha-