title: The Ras-binding domain region of RGS14 regulates its functional interactions with heterotrimeric G proteins.
abstract: RGS14 is a 60 kDa protein that contains a regulator of G protein signaling (RGS) domain near its N-terminus, a central region containing a pair of tandem Ras-binding domains (RBD), and a GPSM (G protein signaling modulator) domain (a.k.a. Gi/o-Loco binding [GoLoco] motif) near its C-terminus. The RGS domain of RGS14 exhibits GTPase accelerating protein (GAP) activity toward Gαi/o proteins, while its GPSM domain acts as a guanine nucleotide dissociation inhibitor (GDI) on Gαi1 and Gαi3. In the current study, we investigate the contribution of different domains of RGS14 to its biochemical functions. Here we show that the full-length protein has a greater GTPase activating activity but a weaker inhibition of nucleotide dissociation relative to its isolated RGS and GPSM regions, respectively. Our data suggest that these differences may be attributable to an inter-domain interaction within RGS14 that promotes the activity of the RGS domain, but simultaneously inhibits the activity of the GPSM domain. The RBD region seems to play an essential role in this regulatory activity. Moreover, this region of RGS14 is also able to bind to members of the B/R4 subfamily of RGS proteins and enhance their effects on GPCR-activated Gi/o proteins. Overall, our results suggest a mechanism wherein the RBD region associates with the RGS domain region, producing an intramolecular interaction within RGS14 that enhances the GTPase activating function of its RGS domain while disfavoring the negative effect of its GPSM domain on nucleotide dissociation.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Peishen
authors.initials: P
authors.lastname: Zhao
authors.forename: Caroline
authors.initials: C
authors.lastname: Nunn
authors.forename: Suneela
authors.initials: S
authors.lastname: Ramineni
authors.forename: John R
authors.initials: JR
authors.lastname: Hepler
authors.forename: Peter
authors.initials: P
authors.lastname: Chidiac
mesh_terms: D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004789:Enzyme Activation; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D018727:Muscarinic Antagonists / Q000494:pharmacology; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020710:RGS Proteins / Q000737:chemistry / Q000502:physiology*; D043585:Receptor, Muscarinic M2 / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D061987:Sf9 Cells; D015398:Signal Transduction; D014331:Tropicamide / Q000494:pharmacology
chemical_list: C487078:CHRM2 protein, human; D018679:Cholinergic Agonists; D018727:Muscarinic Antagonists; D020710:RGS Proteins; C491400:RGS14 protein, human; D043585:Receptor, Muscarinic M2; D018341:Receptors, Adrenergic, alpha-2; D002217:Carbachol; D020962:Heterotrimeric GTP-Binding Proteins; D014331:Tropicamide