Site-directed mutations in the third intracellular loop of the serotonin 5-HT(1A) receptor alter G protein coupling from G(i) to G(s) in a ligand-dependent manner.
The effect of mutations (V344E and T343A/V344E) in the third intracellular loop of the serotonin 5-HT(1A) receptor expressed transiently in human embryonic kidney 293 cells have been examined in terms of receptor/G protein interaction and signaling. Serotonin, (R)-8-hydroxy-2-dipropylaminotetralin [(R)-8-OH-DPAT], and buspirone inhibited cyclic AMP production in cells expressing native and mutant 5-HT(1A) receptors. Serotonin, however, produced inverse bell-shaped cyclic AMP concentration-response curves at native and mutant 5-HT(1A) receptors, indicating coupling not only to G(i)/G(o), but also to G(s). (R)-8-OH-DPAT, however, induced stimulation of cyclic AMP production only after inactivation of G(i)/G(o) proteins by pertussis toxin and only at the mutant receptors. The partial agonist buspirone was unable to induce coupling to G(s) at any of the receptors, even after pertussis toxin treatment. The basal activities of native and mutant 5-HT(1A) receptors in suppressing cyclic AMP levels were not found to be significantly different. The receptor binding characteristics of the native and mutant receptors were investigated using the novel 5-HT(1A) receptor antagonist [(3)H]NAD-299. For other receptors, analogous mutations have produced constitutive activation. This does not occur for the 5-HT(1A) receptor, and for this receptor the mutations seem to alter receptor/G protein coupling, allowing ligand-dependent coupling of receptor to G(s) in addition to G(i)/G(o) proteins.
Department of Biosciences, The University, Canterbury, Kent, England. asa.malmberg@astrazeneca.com
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D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000595:Amino Acid Sequence; D001578:Benzopyrans / Q000493:pharmacokinetics; D002065:Buspirone / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D037342:Pertussis Toxin; D017433:Protein Structure, Secondary; D011985:Receptors, Serotonin / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1; D011994:Recombinant Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000493:pharmacokinetics; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D001578:Benzopyrans; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D011994:Recombinant Proteins; D012702:Serotonin Antagonists; D010566:Virulence Factors, Bordetella; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; C108607:robalzotan; D002065:Buspirone