Two-dimensional 1H NMR study of a tetradecapeptide with the consensus sequence Arg5-Asp-Val-Arg-Gly9: structural effects of the outside substitution Ser12 by Ala12

The mu-selective heptapeptide opioid dermorphin has two conformations around Phe3 psi with no head-to-tail interaction. A quantitative 2-D NMR and molecular modeling analysis

The mu opioid heptapeptide Dermorphin (DRM) is under 70 % of trans forms for the Tyr(5)-Pro(6) peptide bond in solution (CDCl(3)/DMSO-d(6) 1/1 vol/vol). Variations of NOE integrals at 5 temperatures show apparent correlation times of 0.8 to 0.9 ns (at 280 K) in that mixed solvent. Four NOE between non-adjacent residues reveal a large population of folded structures. However, in trans DRM, 4 adjacent NOE Phe(3)/Gly(4) can only be explained by an equilibrium between folded (psi(3) > 0) and extended (psi(3) > 0) conformations. Simulated annealing modeling gave about 60% (psi(3) > 0) and 40% (psi(3) > 0) of these conformer populations. Trans DRM study and previous studies on the heptapeptide opioids, dermenkephalin (DREK) and deltorphin-I (delta selective), and DREK(1-4)-DRM(5-7) hybrid (mu selective), show in folded structures more backbone bending of the first 4 residues in the mu opioids than in the delta peptides. Also, the main difference between mu- and delta-opioid peptides is a large fraction of extended conformations in mu heptapeptides. Either bending of the N-terminus, or extension of the C-terminal part in mu-opioid heptapeptides prevent the head-to-tail interactions which allow delta-opioid peptides to bind selectively to the delta-opioid receptor.

The delta-selective opioid peptide dermenkephalin and the mu-selective hybrid peptide dermenkephalin-[1-4]-dermophin-[5-7] display strikingly different conformations despite identical tetrapeptide N-termini. A quantitative 2-D NMR and molecular modeling analysis

The selective recognition of the aminoterminal binding pharmacophore Tyr-D-Xaa-Phe of the opioid heptapeptide dermorphin, Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2 (DRM)1, and of dermenkephalin, Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2 (DREK), by the mu-opioid receptor and delta-opioid receptor, respectively, depends upon the constitution / conformation of the C-terminal tripeptide. The hybrid peptide DREK-[1-4]-DRM-[5-7] is very potent at, and exquisitely selective for the mu-opioid receptor, and differs only from dermenkephalin by its C-terminal tripeptide. Comparison of the structural features of DREK-[1-4]-DRM-[5-7] and dermenkephalin by nmr analysis and molecular modeling revealed striking differences, as well in the trans (Tyr5 - Pro6) isomer (population 75%) than in the cis isomer.. Whereas the folded C-terminal tail of dermenkephalin influenced the tertiary structure of the N-terminal tetrapeptide and placed the Tyr1 and Phe3 aromatic rings in definite orientations that are best suited for the delta-receptor, there were only weak contacts, as shown by NOE data, between the aminoterminal and carboxyterminal parts of the hybrid peptide. This promoted increased flexibility of the whole backbone and relaxed orientations for the side-chains of Tyr1 and Phe3 that are compatible with the mu-receptor but unsuitable for the delta-receptor. The steric hindrance introduced by Pro6 in DREK-[1-4]-DRM-[5-7], plus the absence of large hydrophobic side-chains in positions 5 and 6 may prevent close contacts between the N-terminal and C-terminal domains and reorientation of the main pharmacophoric elements Tyr1 and Phe3.

Solution conformations of deltorphin-I obtained from combined use of quantitative 2D-NMR and energy calculations: a comparison with dermenkephalin

Deltorphin-I, Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2 and dermenkephalin, Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, two highly related opioid peptides from frog skin, display very similar N-termini but strikingly different C-terminal tails. Nevertheless, both peptides are highly potent at, and exquisitely selective for the delta-opioid receptor. To identify common determinants concuring to the remarkably efficient targeting of deltorphin-I and dermenkephalin, combined use of quantitative two-dimensional nuclear magnetic resonance (53 dipolar interactions studied at four temperatures) and energy calculations using simulated annealing generated five groups of deltorphin-I conformers. These groups were pooled into two families whose overall conformation could be described either by a left-handed helix (Family I) or by a big loop (Family II), both stabilized by H-bonds. Proximity of D-Ala2-Phe3-Asp4 and Val5-Val6-Gly7 triads is an obvious structural similarity between almost all groups in both families of structures. Whereas differences between the two families originated mostly from a transition at psi Asp4 backbone dihedral angle, the backbone structures at segment 1-4 are similar and spatial arrangements of Tyr1 (t) and Phe3 (g-) are identical in one group of each family. Moreover, these two groups have a N-terminal tetrapeptide whose conformation most closely resembles that of a well-defined group of structures for dermenkephalin. Altogether, these results suggest that conformational attributes that are common to dermenkephalin and deltorphin-I, i.e., the backbone conformation of the N-terminal tetrapeptide and preferential orientations in the side-chain of Tyr1 (t) and Phe3 (g-) underlie their ability to bind with high selectivity to the delta-opioid receptor.

Conformational study based on simulated annealing and 1H NMR of peptides comprising the consensus sequence Arg5-Asp-Val-Arg-Gly9: effects of the substitution Ser 12 by Ala 12 or of 3 residues deletion at the N-terminus

A conformational search by simulated annealing has been performed on two peptides derivated from the tetradecapeptide used to isolate the Xenopus laevis skin maturation RXVRG-endoprotease. The Ala 12 derivative, obtained by substitution in the hydrophobic C terminal fragment and the undecapeptide 4-14, obtained by deletion of an acidic rich tripeptide, were studied. No unique structure has been found for the tetradecapeptide Ala 12. This structural disorganization could explain the loss of activity of the endoprotease towards the substituted peptide. For the undecapeptide, two different models in accordance with the NMR data were found. The conformational differences between these two models are located in the consensus sequence and in each case an hairpin-like conformation is observed. These results could be related to the enhanced cleavage activity of the maturation enzyme. The obtained structures are also compared with those of the original tetradecapeptide.