Opioid peptide

Vertebrate endogenous opioids neuropeptide
Identifiers
Symbol	Opiods_neuropep
Pfam	PF01160
InterPro	IPR006024
PROSITE	PDOC00964
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Structural correlation between met-enkephalin, an opioid peptide, (left) and morphine, an opiate drug, (right)

Opioid peptides are short sequences of amino acids 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.

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.^[1]

Opioid peptides 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.^[2] The POMC gene codes for endogenous opioids such as β-endorphin and gamma-endorphin.^[3] 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.^[4]
• 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.^[5]
• The PNOC gene encoding prepronociceptin, which is cleaved into nociceptin and potentially two additional neuropeptides.^[1]
• 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.

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

1. Mollereau C, Simons MJ, Soularue P, Liners F, Vassart G, Meunier JC, Parmentier M (August 1996). "Structure, tissue distribution, and chromosomal localization of the prepronociceptin gene". Proc. Natl. Acad. Sci. U.S.A. 93 (16): 8666–70. doi:10.1073/pnas.93.16.8666. PMC 38730. PMID 8710928.
2. Chang AC, Cochet M, Cohen SN (August 1980). "Structural organization of human genomic DNA encoding the pro-opiomelanocortin peptide". Proc. Natl. Acad. Sci. U.S.A. 77 (8): 4890–4. doi:10.1073/pnas.77.8.4890. PMC 349954. PMID 6254047.
3. Ling N, Burgus R, Guillemin R (November 1976). "Isolation, primary structure, and synthesis of alpha-endorphin and gamma-endorphin, two peptides of hypothalamic-hypophysial origin with morphinomimetic activity". Proc. Natl. Acad. Sci. U.S.A. 73 (11): 3942–6. doi:10.1073/pnas.73.11.3942. PMC 431275. PMID 1069261.
4. Noda M, Teranishi Y, Takahashi H, Toyosato M, Notake M, Nakanishi S, Numa S (June 1982). "Isolation and structural organization of the human preproenkephalin gene". Nature 297 (5865): 431–4. doi:10.1038/297431a0. PMID 6281660.
5. Horikawa S, Takai T, Toyosato M, Takahashi H, Noda M, Kakidani H, et al. (Dec 1983). "Isolation and structural organization of the human preproenkephalin B gene". Nature 306 (5943): 611–4. doi:10.1038/306611a0. PMID 6316163.

External links

• Opioid Peptides at the US National Library of Medicine Medical Subject Headings (MeSH)

This article incorporates text from the public domain Pfam and InterPro IPR006024