Opioid receptors from a lower vertebrate (Catostomus commersoni): sequence, pharmacology, coupling to a G-protein-gated inward-rectifying potassium channel (GIRK1), and evolution.
The molecular evolution of the opioid receptor family has been studied by isolating cDNAs that encode six distinct opioid receptor-like proteins from a lower vertebrate, the teleost fish Catostomus commersoni. One of these, which has been obtained in full-length form, encodes a 383-amino acid protein that exhibits greatest sequence similarity to mammalian mu-opioid receptors; the corresponding gene is expressed predominantly in brain and pituitary. Transfection of the teleost cDNA into HEK 293 cells resulted in the appearance of a receptor having high affinity for the mu-selective agonist [D-Ala2, MePhe4-Gly-ol5]enkephalin (DAMGO) (Kd = 0.63 +/- 0.15 nM) and for the nonselective antagonist naloxone (Kd = 3.1 +/- 1.3 nM). The receptor had negligible affinity for U50488 and [D-Pen2, D-Pen5]enkephalin (DPDPE), which are kappa- and delta-opioid receptor selective agonists, respectively. Stimulation of transfected cells with 1 microM DAMGO lowered forskolin-induced cAMP levels, an effect that could be reversed by naloxone. Experiments in Xenopus oocytes have demonstrated that the fish opioid receptor can, in an agonist-dependent fashion, activate a coexpressed mouse G-protein-gated inward-rectifying potassium channel (GIRK1). The identification of six distinct fish opioid receptor-like proteins suggests that additional mammalian opioid receptors remain to be identified at the molecular level. Furthermore, our data indicate that the mu-opioid receptor arose very early in evolution, perhaps before the appearance of vertebrates, and that the pharmacological and functional properties of this receptor have been conserved over a period of approximately 400 million years implying that it fulfills an important physiological role.
Darlison
M G
MG
Institut für Zellbiochemie und klinische Neurobiologie, Universität Hamburg, Martinistrasse 52, D-20246 Hamburg, Germany.
Greten
F R
FR
Harvey
R J
RJ
Kreienkamp
H J
HJ
Stühmer
T
T
Zwiers
H
H
Lederis
K
K
Richter
D
D
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary; D019143:Evolution, Molecular; D005399:Fishes / Q000235:genetics*; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D006801:Humans; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011485:Protein Binding; D011869:Radioligand Assay; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D018076:DNA, Complementary; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D017450:Receptors, Opioid, mu