Conformational analysis of the endogenous μ‐opioid agonist endomorphin‐1 using NMR spectroscopy and molecular modeling

Abstract

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH P ) is a highly selective and potent agonist of the W W-opioid receptor. To identify structural attributes unique to this opioid peptide and potential sites of recognition, a conformational analysis has been performed using multidimensional NMR and molecular modeling techniques. The spectroscopic results, derived from experiments in both DMSO and water, indicate that endomorphin-1 exists in the cis-and trans-configuration with respect to the Pro-omega bond in approximately 25% and 75% populations, respectively. In DMSO, the cis-configuration adopts a compact sandwich conformation in which the Tyr and Trp aromatic rings pack against the proline ring, whereas the trans-configuration adopts an extended conformation. Although non-random structure was not observed in water, condensed phase molecular dynamics calculations indicate that trans-isomers dominate the population in this higher dielectric medium. Structural comparison of the cis-and trans-configurations with morphine and selective W Wpeptide ligands PL-017 and D-TIPP, as well as the N N-selective peptide ligands TIPP (N N-antagonist, W W-agonist) and DPDPE were also performed and suggest the trans-isomer is likely the bioactive form. A hypothesis is proposed to explain W W-and N Nselectivity based on the presence of spatially distinct selectivity pockets among these ligands.z 1998 Federation of European Biochemical Societies.

The Endomorphin System and Its Evolving Neurophysiological Role

“…The sequence of endomorphins also includes a spacer (Pro), which joins the pharmacophoric residues. Podlogar et al (1998) presented a Pro-opiomelanocortin…”

Conformational Similarities and Dissimilarities Between the Stereoisomeric Forms of Endomorphin‐2

“…Nevertheless, other earlier experimental and computational studies carried out on the EM1 and various EM derivatives provided also information about the rotamer states of the side chain of aromatic amino acids. In the case of the trans-isomer of EM1, the data derived from NMR measurements indicated that the side chain of Tyr 1 residue could adopt the trans rotamer; however, based on the results obtained from MD simulations, this side chain was found to be characterized by the g ()) rotamer state (23 4 ]EM2 derivatives pointed out that the side chain of Tyr 1 residue showed a preference for the trans rotamer in the case of cis-isomers, while the g ()) rotamer was detected as the preferred conformation of the side chain of Phe 3 amino acid in the case of both cis-and trans-isomers (13). Moreover, the results of this NMR study indicated that the g(+) rotamer was favored for the side chain of the bMePhe 4 …”

“…Other earlier experimental and computational studies also pointed out that various intramolecular H-bonds could be observed for the conformational states of EMs and their derivatives. In the case of the trans-isomer of EM1, during the MD simulation, the Tyr 1 -CO ‹ Phe 4 -NH H-bond appeared, playing a role in the structural stabilization of type III b-turn; furthermore, an additional H-bond evolved between the Pro 2 -CO and C-terminal NH 2 groups was detected (23). Based on the results of NMR measurement combined with SA calculation, the rS-type open conformer of the trans-isomer of EM2 was found to be stabilized by two intramolecular H-bonds, such as the Tyr Aromatic-aromatic and proline-aromatic interactions In the case of peptides, not only the intramolecular H-bonds but other interactions (e.g., aromatic-aromatic and proline-aromatic interplays) also play a relevant role in the determination and stabilization of their 3D structure.…”

Design, synthesis and pharmacological evaluation of novel endomorphin analogues with multiple structural modifications

“…Hence endomorphins contain Pro in position 2, they exist as an equilibrium mixture of cis-and trans-conformations [48] Consequently, the bioactive conformations of endomorphins remained an unanswered question. However, a slightly bent backbone structure was proposed for receptor-bound ligands, more recently four structural parameters were confirmed for high µ-opioid activity.…”