Rahul Sharma (Editor)

Opioid peptide

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Symbol
  
Opiods_neuropep

InterPro
  
IPR006024

Pfam
  
structures

Pfam
  
PF01160

PROSITE
  
PDOC00964

PDB
  
RCSB PDB; PDBe; PDBj

Opioid peptide

Opioid peptides are peptides that bind to opioid receptors in the brain; opiates and opioids mimic the effect of these peptides. Such peptides may be produced by the body itself, for example endorphins. The effects of these peptides vary, but they all resemble those of opiates. Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, and the control of food intake.

Contents

Opioid-like peptides may also be absorbed from partially digested food (casomorphins, exorphins, and rubiscolins). The opioid food peptides have lengths of typically 4–8 amino acids. The body's own opioids are generally much longer.

Opioid peptides are released by post-translational proteolytic cleavage of precursor proteins. The precursors consist of the following components: a signal sequence that precedes a conserved region of about 50 residues; a variable-length region; and the sequence of the neuropeptides themselves. Sequence analysis reveals that the conserved N-terminal region of the precursors contains 6 cysteines, which are probably involved in disulfide bond formation. It is speculated that this region might be important for neuropeptide processing.

Endogenous opioids produced by the body

The human genome contains several homologous genes that are known to code for endogenous opioid peptides.

  • The nucleotide sequence of the human gene for proopiomelanocortin (POMC) was characterized in 1980. The POMC gene codes for endogenous opioids such as β-endorphin and gamma-endorphin. The peptides with opioid activity that are derived from proopiomelanocortin comprise the class of endogenous opioid peptides called "endorphins".
  • The human gene for the enkephalins was isolated and its sequence described in 1982.
  • The human gene for dynorphins (originally called the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983.
  • The PNOC gene encoding prepronociceptin, which is cleaved into nociceptin and potentially two additional neuropeptides.
  • Adrenorphin, amidorphin, and leumorphin were discovered in the 1980s.
  • The endomorphins were discovered in the 1990s.
  • Opiorphin and spinorphin, enkephalinase inhibitors (i.e., prevent the metabolism of enkephalins).
  • Hemorphins, hemoglobin-derived opioid peptides, including hemorphin-4, valorphin, and spinorphin, among others.
  • While not peptides, codeine and morphine are also produced in the human body.
  • Opioid food peptides

  • Casomorphin (from casein found in milk of mammals, including cows)
  • Gluten exorphin (from gluten found in wheat, rye, barley)
  • Gliadorphin/gluteomorphin (from gluten found in wheat, rye, barley)
  • Soymorphin-5 (from soybean)
  • Rubiscolin (from spinach)
  • Amphibian opioid peptides

  • Deltorphin I and II
  • Dermorphin
  • Synthetic opioid peptides

  • Zyklophin – semisynthetic KOR antagonist derived from dynorphin A
  • References

    Opioid peptide Wikipedia