T. Ebisawa et al., EXPRESSION CLONING OF A HIGH-AFFINITY MELATONIN RECEPTOR FROM XENOPUSDERMAL MELANOPHORES, Proceedings of the National Academy of Sciences of the United Statesof America, 91(13), 1994, pp. 6133-6137
Using an expression cloning strategy, a high-affinity melatonin recept
or cDNA has been isolated from Xenopus laevis dermal melanophores. Tra
nsient expression of the cDNA in COS-7 cells resulted in high-affinity
2-[I-125]- iodomelatonin binding (K-d = 6.3 +/- 0.3 X 10(-11) M). In
addition, six ligands exhibited a rank order of inhibition of specific
2-[I-125] iodomelatonin binding that was identical to that reported f
or endogenous high-affinity receptors. Functional studies of CHO cells
stably expressing the receptor cDNA showed that melatonin acting thro
ugh the cloned receptor inhibited forskolin-stimulated cAMP accumulati
on in a dose-dependent manner. Northern blot analysis showed that mela
tonin receptor transcripts are moderately expressed in Xenopus dermal
melanophores. The cDNA encodes a protein of 420 amino acids, which con
tains seven hydrophobic segments. Structural analysis revealed that th
e receptor protein is a newly discovered member of the guanine nucleot
ide binding protein-coupled receptor family.