Specific receptor for the opioid peptide dynorphin: structure--activity relationships

Area of Science:

• Pharmacology
• Neuroscience
• Molecular Biology

Background:

• Opioid peptides, such as dynorphin, play significant roles in pain modulation and other physiological processes.
• Understanding the structure-activity relationships of dynorphin is crucial for developing targeted therapeutics.
• The guinea pig ileum myenteric plexus is a well-established model for studying opioid receptor interactions.

Purpose of the Study:

• To investigate the specific structural features of dynorphin responsible for its high potency and selectivity for opioid receptors.
• To identify critical amino acid residues and modifications influencing dynorphin's biological activity and receptor binding.

Main Methods:

• Systematic deletion of COOH-terminal amino acids from dynorphin-(1--13).
• Modification of specific amino acid residues, including N-terminal and internal substitutions.
• Assessment of biological activity and potency through functional assays in the guinea pig ileum myenteric plexus.

Main Results:

• Removal of COOH-terminal lysine-13, lysine-11, and arginine-7 significantly impacted dynorphin's potency.
• Abolition of biological activity was observed upon removal of the NH2-terminal tyrosine.
• Substitution of D-alanine for glycine-2 reduced potency, while COOH-terminal methyl esterification enhanced potency for several dynorphin fragments.
• Lysine-11 and arginine-7 were identified as critical for dynorphin receptor selectivity, distinguishing it from the mu receptor.

Conclusions:

• Specific amino acid residues within the dynorphin sequence are essential for its potent interaction with opioid receptors.
• Dynorphin exhibits receptor selectivity, with distinct structural requirements for binding to the dynorphin receptor versus the mu receptor.
• These findings provide valuable insights into the molecular mechanisms underlying dynorphin's pharmacological effects and receptor interactions.