Abstract
Site-directed mutation of serine 110 (Ser(3.35)) and serine 114 (Ser(3.39)) in the human melatonin MT(1) receptor to alanine residues reduced ligand binding affinities of seven known melatonin receptor agonists and partial agonists by 3- to 15-fold. These mutants also displayed a relative reduction in their affinities for melatonin-mediated functional responses of 30- and 14-fold, respectively. In contrast to the observed effects of the agonists and partial agonists, the melatonin receptor antagonist luzindole was found to bind to mutants Ser(3.35)Ala and Ser(3.39)Ala with affinities equivalent to that determined for the wild-type melatonin MT(1) receptor. Luzindole was subsequently confirmed as an antagonist of melatonin-mediated functional responses for both mutant receptors. These studies have identified that in the human melatonin MT(1) receptor, Ser(3.35) and Ser(3.39), in transmembrane domain 3, are critical for the formation of the high-affinity ligand binding site for agonists and partial agonists but not for the antagonist luzindole.
Copyright 2001 Academic Press.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Acetamides / pharmacology
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Amides / pharmacology
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Amino Acid Substitution
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Animals
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Binding Sites / genetics
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Binding, Competitive / drug effects
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COS Cells
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Cyclic AMP / metabolism
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Dose-Response Relationship, Drug
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Heterotrimeric GTP-Binding Proteins / genetics
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Heterotrimeric GTP-Binding Proteins / metabolism
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Humans
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Indoles / pharmacology
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Melatonin / analogs & derivatives
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Melatonin / pharmacology
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Mutagenesis, Site-Directed
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Naphthalenes / pharmacology
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Protein Binding / drug effects
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Radioligand Assay
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Receptors, Cell Surface / agonists
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Receptors, Cell Surface / antagonists & inhibitors
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Receptors, Cell Surface / genetics
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Receptors, Cell Surface / metabolism*
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Receptors, Cytoplasmic and Nuclear / agonists
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Receptors, Cytoplasmic and Nuclear / antagonists & inhibitors
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Receptors, Cytoplasmic and Nuclear / genetics
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Receptors, Cytoplasmic and Nuclear / metabolism*
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Receptors, Melatonin
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Serine / genetics
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Serine / metabolism*
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Structure-Activity Relationship
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Transfection
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Tryptamines / pharmacology
Substances
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Acetamides
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Amides
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Indoles
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Naphthalenes
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Receptors, Cell Surface
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Receptors, Cytoplasmic and Nuclear
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Receptors, Melatonin
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Recombinant Fusion Proteins
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S 20642
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Tryptamines
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N-acetyltryptamine
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luzindole
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agomelatine
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Serine
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methoxytryptophol
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2-iodomelatonin
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Cyclic AMP
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Heterotrimeric GTP-Binding Proteins
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Melatonin