ASIP is an endogenous antagonist of melanocortin receptors (MCRs) and plays crucial roles in the regulation of pigmentation. ASIP acts normally as a competitive antagonist of melanocortin peptides at MC1R to block cAMP synthesis, leading to a downregulation of eumelanogenesis and upregulation of pheomelanogenesis. Beyond competitive antagonism, in vitro assays show that this protein can act as an inverse agonist to decrease basal receptor activity in the absence of melanocortin peptides. ASIP also has a role in regulating lipid metabolism in adipocytes in humans, bovines, and chickens. The ASIP gene encodes a protein with a putative signal peptide sequence and a cysteine-rich C-terminal domain which is sufficient for potent antagonist function. The Arg–Phe–Phe triplet in the C-terminal domains is essential for binding and antagonist function at melanocortin receptors. The N-terminal domain of ASIP acts as a ligand for an accessory receptor, Attractin.

Original languageEnglish
Title of host publicationHandbook of Hormones
Subtitle of host publicationComparative Endocrinology for Basic and Clinical Research
Number of pages2
ISBN (Electronic)9780128010280
ISBN (Print)9780128010679
Publication statusPublished - Jan 1 2015


  • antagonist
  • inhibitor cysteine knot (ICK) protein
  • inverse agonist
  • knottin
  • melanocortin receptor

ASJC Scopus subject areas

  • General Medicine


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