Impact of T161, Y318 and S363 alanine mutations on regulation of the human delta-opioid receptor (hDOPr) induced by peptidic and alkaloid agonists

Previously, we showed a differential regulation of the human delta-opioid receptor (hDOPr) by etorphine and [D-Pen², D-Pen⁵] enkephalin (DPDPE). To understand the molecular basis of such differences, we introduced 3 alanine mutations at the residues T161. Y318 and S363. Both wild type (WT) and hDOPr mutants were expressed in HEK cells containing endogenous arrestins or CFP-tagged arrestin 3, then desensitization, internalization, recycling and phosphorylation were studied. In a context of endogenous arrestin expression, a major difference in DOPr desensitization was observed between agonists that was modified with the T161A mutation upon etorphine and with the S363A substitution upon DPDPE exposure. While both agonists induced a major receptor internalization, T161A and S363A impaired DOPr sequestration only for etorphine. However, similar level of S363 phosphorylation was measured between agonists. When CFP-tagged arrestin 3 was over-expressed, a similar profile of desensitization was measured for both agonists. In this context, all the 3 alanine mutations decreased etorphine-induced receptor desensitization. Using FRET, we showed similar interactions between WT hDOPr and arrestin 3 under DPDPE and etorphine stimulation which were delayed by both the Y318A and the S363A substitutions for etorphine. Finally, hDOPr recycling was qualitatively evaluated by microscopy and showed neither arrestin 3/hDOPr colocalization nor major impact of alanine mutations except for the S363A which impaired internalization and recycling for etorphine. The T161, Y318 and S363 residues of hDOPr could underlie the differential regulation promoted by DPDPE and etorphine.

Bradykinin analogs containing the 4-amino-2-benzazepin-3-one scaffold at the C-terminus

High affinity peptide ligands for the bradykinin (BK) B(2) subtype receptor have been shown to adopt a beta-turn conformation of the C-terminal tetrapeptide (H-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH). We investigated the replacement of the Pro(7)-Phe(8) dipeptide moiety in BK or the D-Tic(7)-Oic(8) subunit in HOE140 (H-D-Arg(0)-Arg(1)-Pro(2)-Hyp(3)-Gly(4)-Thi(5)-Ser(6)-D-Tic(7)-Oic(8)-Arg(9)-OH) by 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one templates (Aba). Binding studies to the human B(2) receptor showed a correlation between the affinities of the BK analogs and the propensity of the templates to adopt a beta-turn conformation. The L-spiro-Aba-Gly containing HOE140 analog BK10 has the best affinity, which correlates with the known turn-inducing property of this template. All the compounds did not modify basal inositolphosphate (IP) output in B(2)-expressing CHO cells up to 10 microM concentration. The antagonist properties were confirmed by the guinea pig ileum smooth muscle contractility assay. The new amino-benzazepinone (Aba) substituted BK analogs were found to be surmountable antagonists.

Direct chiral separation of unnatural amino acids by high-performance liquid chromatography on a ristocetin a-bonded stationary phase

Direct high-performance liquid chromatographic chiral separation of numerous underivatized unnatural amino acids on a ristocetin A-bonded chiral stationary phase used in the reversed-phase and in the polar organic chromatographic modes is reported. The effects of different parameters such as mobile phase composition, temperature, and the structure of the analytes on the selectivity in both chromatographic modes are discussed. By variation of the parameters, the separation of the stereoisomers was optimized and, as a result, baseline resolution was achieved in most cases.

Binding characteristics of the novel highly selective delta agonist, [3H]IIe5,6deltorphin II

Following the description of the [3H]deltorphin II, it has been reported that the modification of deltorphin II with the substitution of Val5,6 residues by the more hydrophobic IIe5,6 residues leads to an increased affinity and selectivity. The IIe5,6 deltorphin II (Tyr-D-Ala-Phe-Gly-IIe-IIe-HH2) was tritiated by catalytic dehalogenation and labelled rat brain membrane sites with a Kd value of 0.40 nM and a Bmax of 121 fmol/mg protein. Competition binding experiments with various unlabelled subtype specific opioid receptor ligands resulted in mu/delta and kappa/delta selectivity ratios of 2400 and 18,000 respectively. Due to its high delta receptor affinity, delta selectivity and very low non-specific binding (< 20%), [3H]IIe5,6 deltorphin II, is a very useful tool for the identification and characterisation of delta opioid receptors.