Examination of the conformational meaning of "delta-address" in the dermenkephalin sequence

Comprehensive energy calculations were applied to four opioid-related peptides with different receptor selectivities, namely the delta-selective dermenkephalin (Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, DRE), the mu-selective dermorphin (Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2, DRM) and their "hybrid" peptides DRM/DRE (Tyr-D-Ala-Phe-Gly-Leu-Met-Asp-NH2) and DRE/DRM (Tyr-D-Met-Phe-His-Tyr-Pro-Ser-NH2). It was shown that the N-terminal tripeptide "mu-messages" in the delta-selective ligands DRE and DRM/DRE can possess similar low energy space arrangements of their functionally important elements (the N-terminal alpha-amino group and the aromatic moieties of Tyr and Phe), but that these are different from the space arrangement of these moieties in mu-selective DRM and DRE/DRM. These results suggest that the C-terminal tripeptide "delta-address" in DRE may influence the conformation of the "mu-message" in DRM. A refined model for the delta-receptor-bound conformation of DRE is proposed based on these calculations which is similar to that previously suggested for the cyclic delta-selective peptide [D-Pen2, D-Pen5]enkephalin (DPDPE). This model also has partial correspondence with the structure of the delta-selective alkaloid naltrindole.