Function of negative charge in the "address domain" of deltorphins.
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.
Lazarus
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Peptide Neurochemistry Section, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Salvadori
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Santagada
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Tomatis
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Wilson
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D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine / Q000031:analogs & derivatives / Q000378:metabolism; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D013329:Structure-Activity Relationship
D009842:Oligopeptides; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; C059567:deltorphin; D016308:Enkephalin, Leucine-2-Alanine; C030279:enkephalinamide-Leu, Ala(2)-