title: Insight into the mechanism of dopamine D1-like receptor activation. Evidence for a molecular interplay between the third extracellular loop and the cytoplasmic tail.
abstract: A chimeric D1A dopaminergic receptor harboring the cytoplasmic tail (CT) of the D1B subtype (D1A-CTB) has been used previously to show that CT imparts high dopamine (DA) affinity and constitutive activity to the D1B receptors. However, the D1A-CTB chimera, unlike the D1B subtype, exhibits a significantly lower DA potency for stimulating adenylyl cyclase and a drastically lower maximal binding capacity (Bmax). Here, using a functional complementation of chimeric D1-like receptors, we have identified the human D1B receptor regions regulating the intramolecular relationships that lead to an increased DA potency and contribute to Bmax. We demonstrate that the addition of variant residues of the third extracellular loop (EL3) of the human D1B receptor into D1A-CTB chimera leads to a constitutively active mutant receptor displaying an increased DA affinity, potency, and Bmax. These results strongly suggest that constitutively active D1-like receptors can adopt multiple active conformations, notably one that confers increased DA affinity with decreased DA potency and Bmax and another that imparts increased DA affinity with a strikingly increased DA potency and Bmax. Overall, we show that a novel molecular interplay between EL3 and CT regulates multiple active conformations of D1-like receptors and may have potential implications for other G protein-coupled receptor classes.
authors.affiliation: Ottawa Health Research Institute, Ottawa Hospital (Civic Campus), Ontario K1Y 4K9, Canada.
authors.forename: Katerina
authors.initials: K
authors.lastname: Tumova
authors.forename: Rafal M
authors.initials: RM
authors.lastname: Iwasiow
authors.forename: Mario
authors.initials: M
authors.lastname: Tiberi
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism*; D017931:DNA Primers; D004298:Dopamine / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D011485:Protein Binding; D011869:Radioligand Assay; D017447:Receptors, Dopamine D1 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D017931:DNA Primers; D017447:Receptors, Dopamine D1; D011993:Recombinant Fusion Proteins; D019204:GTP-Binding Proteins; D004298:Dopamine