Conformational analysis of endomorphin-1 by molecular dynamics methods.

Area of Science:

• Biochemistry
• Computational Chemistry
• Pharmacology

Background:

• Endomorphin-1 (EM1) is a selective agonist for the mu-opioid receptor, a key target in pain management.
• Understanding the conformational dynamics of EM1 is crucial for elucidating its receptor binding and activity.
• Previous studies have suggested the importance of peptide conformation in biological activity.

Purpose of the Study:

• To perform a detailed conformational analysis of Endomorphin-1 (EM1).
• To investigate the influence of N-terminal charge states (neutral and cationic) and peptide bond isomers (cis/trans) on EM1 conformation.
• To identify preferred secondary structures and stabilizing interactions within EM1.

Main Methods:

• Simulated annealing and molecular dynamics simulations were employed for conformational analysis.
• NMR data were used to restrain simulations, focusing on Tyr1-Pro2 peptide bond configurations (cis and trans).
• Analysis included Ramachandran plots, side-chain rotamer populations, and distance measurements between key atoms and aromatic rings.

Main Results:

• Preferred conformational regions were identified using Ramachandran plots for EM1.
• Side-chain rotamer populations for Tyr1, Trp3, and Phe4 residues were determined.
• Distinct secondary structures, including beta-turns and gamma-turns, were identified. An N-terminal inverse gamma-turn was observed in trans-EM1 but absent in cis-EM1. Both isomers featured C-terminal gamma-turns stabilized by hydrogen bonds.

Conclusions:

• EM1 adopts preferred conformations characterized by beta- and gamma-turns, stabilized by intramolecular hydrogen bonds.
• The conformation of EM1, particularly the presence of an N-terminal inverse gamma-turn, is influenced by the cis/trans isomerism of the Tyr1-Pro2 peptide bond.
• These conformational findings provide insights into the structure-activity relationship of EM1 at the mu-opioid receptor.