Identification of the sorting signal motif within pro-opiomelanocortin for the regulated secretory pathway

D R Cool, M Fenger, C R Snell, Y P Loh

140 Citations (Scopus)

Abstract

The NH2-terminal region of pro-opiomelanocortin (POMC) is highly conserved across species, having two disulfide bridges that cause the formation of an amphipathic hairpin loop structure between the 2nd and 3rd cysteine residues (Cys8 to Cys20). The role that the NH2-terminal region of pro-opiomelanocortin plays in acting as a molecular sorting signal for the regulated secretory pathway was investigated by using site-directed mutagenesis either to disrupt one or more of the disulfide bridges or to delete the amphipathic loop entirely. When POMC was expressed in Neuro-2a cells, ACTH immunoreactive material was localized in punctate secretory granules in the cell body and along the neurites, with heavy labeling at the tips. ACTH was secreted from these POMC-transfected cells in a regulated manner. Disruption of both disulfide bridges or the second disulfide bridge or removal of the amphipathic hairpin loop resulted in constitutive secretion of the mutant POMC from the cells and a lack of punctate secretory granule immunostaining within the cells. We have modeled the NH2-terminal POMC Cys8 to Cys20 domain and have identified it as an amphipathic loop containing four highly conserved hydrophobic and acidic amino acid residues (Asp10-Leu11-Glu14-Leu1). Thus the sorting signal for POMC to the regulated secretory pathway appears to be encoded by a specific conformational motif comprised of a 13-amino acid amphipathic loop structure stabilized by a disulfide bridge, located at the NH2 terminus of the molecule.
Original languageEnglish
JournalJournal of Biological Chemistry
Volume270
Issue number15
Pages (from-to)8723-9
Number of pages6
ISSN0021-9258
Publication statusPublished - 1995

Keywords

  • Amino Acid Sequence
  • Animals
  • Arginine
  • Cattle
  • Cell Line
  • Disulfides
  • Humans
  • Lysine
  • Mice
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Pro-Opiomelanocortin
  • Protein Conformation
  • Protein Sorting Signals
  • Sequence Alignment

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