dermorphin and deltakephalin

Dermorphin (Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2), dermenkephalin (Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2) and deltorphin I (Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2) are the first naturally occurring peptides highly potent for and almost specific to the mu- and delta-opioid receptors, respectively. The amino-terminal domains Tyr-D-X-Phe (where X is either Ala or Met) of these peptides behave as selective and potent mu-receptor ligands. Routing of Tyr-D-X-Phe to the delta- or the mu- receptor is associated with the presence or the absence at the C-terminus of an additional hydrophobic and negatively charged tetrapeptide by-passing the mu-addressing ability of the amino-terminal moiety. A study of 20 Tyr-D-X-Phe-Y-NH2 analogs with substitution of X and Y by neutral, hydrophobic, aromatic amino acids as well as by charged amino acid residues shows that tetrapeptides maintain high binding affinity and selectivity for the mu-opioid receptor. Although residue in position 4 serves a delta-address function, the tripeptide motif at the C-terminus of dermenkephalin and deltorphin I are critical components for high selectivity at delta-opioid receptor. Results demonstrate that mu- and delta-opioid receptors share topologically equivalent ligand-binding domains, or ligand-binding sequences similarities, that recognized Tyr-D-X-Phe as a consensus message-binding sequence. The delta-receptor additionally contains a unique address subsite at or near the conserved binding domain that accommodates the C-terminal tetrapeptide motif of dermenkephalin and deltorphin I.

Topics: Amino Acid Sequence; Animals; Binding Sites; Brain; Cell Membrane; Molecular Sequence Data; Oligopeptides; Opioid Peptides; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu

Processing of the polyprotein precursor pro-dermorphin generates two distantly related D-amino acid-containing peptides, dermorphin and dermenkephalin, which are among the most selective high affinity agonists described, respectively, for the mu- and delta-opioid receptors. Dermenkephalin, Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, is a linear, potentially flexible peptide devoid of structural homology with either enkephalins, endorphins, or dynorphins and, as such, represents a useful tool for identifying determinants of high affinity and selective binding of opioids to the delta-receptor. A series of selected dermenkephalin analogs and homologs was investigated for affinity at the mu- and delta-sites in the brain. Whereas dermenkephalin has high affinity and specificity for the delta-opioid receptors, its tetrapeptide amino end, dermenkephalin-[1-4]-NH2 binds almost exclusively at the mu-receptors. Dermorphin, Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2, is only marginally more selective for the u-sites than is dermenkephalin-[1-4]-NH2. Using dermorphin-dermenkephalin peptide hybrids and C-terminal deletion analogs of dermenkephalin, we showed the critical role that the C-terminal residues Met6 and Asp7 play in specifying correct addressing of dermenkephalin toward delta-receptors. The potent mu-deteminant located within the amino end of dermenkephalin is over-whelmed by the powerful delta-directing ability of the carboxy end. The negatively charged side chain of Asp7 makes a significant contribution to the delta-addressing ability of the C-terminal region, a finding consistent with Schwyzer's membrane selection model (Schwyzer, R. (1986) Biochemistry 25, 6335-6342). The Leu residue in position 5 and D-configuration about the alpha-carbon of Met2 were found to be of crucial importance for high affinity binding to delta-receptors. Whereas the Met residue in position 6 in dermenkephalin could safely be oxidized or replaced with D-Met, oxidation of Met2 led to deleterious effects, this analog being 1/100 as potent as dermenkephalin at delta-sites. Overall, the data collected demonstrate that highest levels of selectivity and affinity for the delta-opioid receptors can be achieved with small-sized, potentially flexible, linear peptides and further support the model according to which, in addition to optimum accommodation at the receptor, selection for delta-receptors is reduced by the effective positive charge of the molecule. Dermenkephalin may provide a starting point for

Topics: Amino Acid Sequence; Animals; Male; Molecular Sequence Data; Oligopeptides; Opioid Peptides; Peptide Fragments; Protein Conformation; Protein Multimerization; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Sequence Homology, Nucleic Acid; Structure-Activity Relationship