Chemical disulfide mapping identifies an inhibitor cystine knot in the agouti signaling protein

FEBS Lett. 2007 Dec 11;581(29):5561-5. doi: 10.1016/j.febslet.2007.10.062. Epub 2007 Nov 13.


The agouti signaling protein (ASIP) and its homolog, the agouti-related protein (AgRP), act as inverse agonists that control, respectively, pigmentation and metabolic function in mammals. NMR investigations find that the C-terminal domains of these proteins adopt a fold consistent with an inhibitor cystine knot (ICK), previously identified in invertebrate toxins. Although these structural studies suggest that ASIP and AgRP define a new mammalian protein fold class, the results with ASIP are inconclusive. Here, we apply direct chemical mapping to determine the complete set of disulfide linkages in ASIP. The results demonstrate unequivocally that ASIP adopts the ICK fold and thereby supports a recent evolution structure function analysis, which proposes that ASIP and AgRP arose from a common antagonist ligand.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Agouti Signaling Protein / chemistry*
  • Agouti Signaling Protein / metabolism
  • Agouti-Related Protein / chemistry
  • Agouti-Related Protein / metabolism
  • Amino Acid Sequence
  • Cystine / chemistry*
  • Cystine / metabolism
  • Disulfides / chemistry*
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Folding
  • Protein Structure, Tertiary
  • Tandem Mass Spectrometry
  • Trypsin / metabolism


  • Agouti Signaling Protein
  • Agouti-Related Protein
  • Disulfides
  • Cystine
  • Trypsin