Function of negative charge in the "address domain" of deltorphins

Abstract

Deltorphins A, B, and C exhibit high delta-affinities (Ki = 0.12-0.31 nM) and very high delta-receptor binding selectivities (Ki mu/Ki delta = 1800-4100). A study of the delta-receptor binding properties of 15 deltorphin analogues focused primarily on the influence of the anionic group in the C-terminal tetrapeptide. Amidation of the beta-carboxyl groups of [Asp7], [Glu4], or [Asp4] in deltorphins A, B, and C, respectively, yielded peptides with enhanced mu-receptor affinities and minor changes in delta-affinities (Ki delta = 0.20-0.65 nM), but 5-8-fold diminished delta-selectivities. A free C-terminal carboxyl group markedly reduced delta-affinities and decreased delta-selectivities 6-11-fold; thus, the C-terminal amide group critically facilitates delta-affinity. Modifications in the anionic charged group or hydrophobic residues in the C-terminal tetrapeptide address domain of deltorphin A altered spatial distributions critical for delta-affinity and selectivity; e.g., [Nle6]deltorphin A enhanced mu-affinity and lowered delta-selectivity by two-thirds; the progressive, step-wise repositioning of Asp in deltorphin C (from position 4 to 7) was accompanied by linear decreases in delta-affinities and -selectivities, and increased mu-affinities of these peptides; enhancement of the charge density to -2, in [Asp6, Asp-OH7]deltorphin A, decreased delta-affinity and -selectivity, while [Asp4,5,His7]deltorphin A bound to neither mu- nor delta-sites. These results demonstrate that while an anionic group may occasionally facilitate high delta-receptor affinity, it represents an absolute requirement for the high delta-binding selectivity of these peptides. The locations of the charged groups relative to hydrophobic residues in the address domain of the peptide are also critical determinants for both delta-affinity and -selectivity.

Synthesis and Pharmacological Activity of Deltorphin and Dermorphin-Related Glycopeptides

“…5,10,16 The present data indicate that the loss of backbone flexibility imposed by the bulky glycosylated Thr 4 in DER and DEL C peptides may presumably limit the opioid binding. 16 The binding properties for µ-and δ-opioid receptors for all of glycopeptides were consistent with the biological activity as tested by GPI and RJ bioassays.…”

Synthesis of Stereoisomeric Analogues of Endomorphin-2, H-Tyr-Pro-Phe-Phe-NH2, and Examination of Their Opioid Receptor Binding Activities and Solution Conformation

“…In fact, the reversed polarity of peptide [8] further demonstrated that the D-configuration in the N-terminal tripeptide was important for the binding mechanism. Of these residues, Pro 2 [11,12,16] and Phe 3 [9] appear to be quite essential: Their D-isomers dramatically reduced affinity. Furthermore the antipode of compound 9 demonstrated the requirement for the simultaneous L-configuration for both Tyr 1 and Pro 2 [10,14].…”

Further Studies on Lead Compounds Containing the Opioid Pharmacophore Dmt-Tic

“…Opioid receptor affinities were determined under equilibrium conditions [2.5 h room temperature (23 °C)] in competition assays using brain P 2 synaptosomal membranes prepared from Sprague-Dawley rats 40, 41. Synaptosomes were preincubated to remove endogenous opioid peptides and stored at −80 °C in buffered 20% glycerol 40, 42.…”