title: Chimeric Galphaq subunits can distinguish the long form of the Xenopus Mel1c melatonin receptor from the mammalian mt1 and MT2 melatonin receptors.
abstract: The family of melatonin receptors is composed of the mt1, MT2, and Mel1c subtypes. The Mel1c is further divided into one long and two short isoforms. A recent study has shown that, unlike mt1 and MT2, the long form of Mel1c is incapable of activating the pertussis toxin-insensitive G16. Here we used three well-characterized Galphaq chimeras to explore the coupling specificity of the melatonin receptors. The qi5, qo5, and qz5 chimeras can link numerous Gi-coupled receptors to the stimulation of phosphoinositide-specific phospholipase C. Both mt1 and MT2 receptors interacted productively with the Galphaq chimeras, while the long form of Mel1c was totally ineffective. Among the Galphaq chimeras, qo5 was less efficiently coupled to the melatonin receptors. Such differential coupling is best explained by structural differences between the melatonin receptors as well as among the Galphaq chimeras. Since the long form of Mel1c receptor possesses an exceptionally large C-terminal tail, we tested the ability of four melatonin receptor C-terminal tail chimeras (Chi 1-4) to interact with the Galphaq chimeras. The presence of the large C-terminal tail of Mel1c in Chi 1 and Chi 3 markedly hindered their coupling to the Galphaq chimeras. On the other hand, the attachment of either the mtl or MT2 C-terminal tail to a Mel1c backbone produced chimeras (Chi 2 and Chi 4) that were capable of activating the Galphaq chimeras. These findings suggest the involvement of C-terminal regions of melatonin receptors in the recognition of G proteins.
authors.affiliation: Department of Biology and the Biotechnology Research Institute, Hong Kong University of Science and Technology, Kowloon, China.
authors.forename: F P
authors.initials: FP
authors.lastname: Lai
authors.forename: S M
authors.initials: SM
authors.lastname: Mody
authors.forename: L Y
authors.initials: LY
authors.lastname: Yung
authors.forename: C S
authors.initials: CS
authors.lastname: Pang
authors.forename: S F
authors.initials: SF
authors.lastname: Pang
authors.forename: Y H
authors.initials: YH
authors.lastname: Wong
mesh_terms: D000818:Animals; D019556:COS Cells / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D015870:Gene Expression; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D044094:Receptors, Melatonin; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D017931:DNA Primers; D007295:Inositol Phosphates; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D011993:Recombinant Fusion Proteins; D000242:Cyclic AMP; D010738:Type C Phospholipases; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins; D043265:Phosphatidylinositol Diacylglycerol-Lyase