scholarly journals Activation of an α2A-adrenoceptor–Gαo1 fusion protein dynamically regulates the palmitoylation status of the G protein but not of the receptor

2004 ◽  
Vol 385 (1) ◽  
pp. 197-206 ◽  
Author(s):  
Elaine BARCLAY ◽  
Mark O'REILLY ◽  
Graeme MILLIGAN
Keyword(s):  
Fusion Protein ◽  
G Protein ◽  
Receptor Agonist ◽  
Ligand Binding Site ◽  
Agonist Binding ◽  
Dynamic Nature ◽  
Α Subunit ◽  
Fusion Construct ◽  
Kinetics Of ◽  
Stimulation Of

Post-translational thio-acylation of a fusion protein between the α2A-adrenoceptor and the α subunit of the G protein Go1 is both dynamic and regulated by agonist binding. Incorporation of [3H]palmitate into the fusion protein was reduced substantially in the presence of the agonist adrenaline. This was dependent on the concentration of adrenaline and correlated with occupancy of the ligand binding site. Both the receptor and G-protein elements of the fusion construct incorporated [3H]palmitate but this occurred more rapidly for the G-protein element and regulation of acylation by the agonist occurred only for the G protein. The kinetics of de-palmitoylation of the α2A-adrenoceptor–Gαo1 fusion were accelerated markedly by agonist. Again, this reflected modulation of the G protein but not of the receptor. Agonist-induced regulation of the kinetics of thio-acylation of the G protein was abolished, however, in a mutant unable to bind guanosine 5′-[γ-[35S]thio]triphosphate ([35S]GTP[S]) in response to adrenaline. Despite the dynamic nature of the post-translational acylation and its regulation by agonist, the ability of adrenaline to activate the G protein, monitored by stimulation of the binding of [35S]GTP[S] to such fusion constructs, was unaffected by the palmitoylation potential of either the receptor or G-protein element.

scholarly journals Measurement of agonist-induced guanine nucleotide turnover by the G-protein Gi1α when constrained within an α2A-adrenoceptor-Gi1α fusion protein

1997 ◽  
Vol 325 (1) ◽  
pp. 17-21 ◽  
Author(s):  
Alan WISE ◽  
I. Craig CARR ◽  
Graeme MILLIGAN
Keyword(s):  
Fusion Protein ◽  
G Protein ◽  
Pertussis Toxin ◽  
Gtpase Activity ◽  
Α Subunit ◽  
Fusion Construct ◽  
High Affinity ◽  
C Terminus ◽  
Adrenoceptor Agonist ◽  
Stimulation Of

A fusion protein was generated between the porcine α2A-adrenoceptor and a pertussis-toxin-insensitive (Cys351 → Gly) variant of the α subunit of Gi1α by direct in-frame fusion of the N-terminus of the G-protein to the C-terminus of the receptor. The fusion protein could be transiently expressed to high levels in COS-7 cells. Addition of the α2-adrenoceptor agonist 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK14304) to membranes of pertussis-toxin-treated transfected cells resulted in a concentration-dependent stimulation of high-affinity GTPase activity. Vmax estimations for the GTPase activity demonstrated an induced catalytic-centre activity of 2.0±0.2 min-1 for Gi1α when the α2A-adrenoceptor was maximally stimulated by UK14304 with a Km for GTP of 0.37±0.07 μM. Co-expression of excess β1γ2 along with the α2A-adrenoceptor-Gi1α fusion protein resulted in greater maximal UK14304-induced stimulation of high-affinity GTPase activity (2.1±0.2-fold) without alteration in agonist EC50. These studies demonstrate the functionality of the fusion construct, its capacity to interact with βγ complex and its utility in measuring agonist regulation of the catalytic-centre activity of GTP by a receptor-associated G-protein.

scholarly journals Impaired noradrenaline-induced lipolysis in white fat of aP2-Ucp1 transgenic mice is associated with changes in G-protein levels

2002 ◽  
Vol 364 (2) ◽  
pp. 369-376 ◽  
Author(s):  
Pavel FLACHS ◽  
JiŘí NOVOTNÝ ◽  
Filip BAUMRUK ◽  
Kristina BARDOVÁ ◽  
Lenka BOUŘOVÁ ◽  
...  
Keyword(s):  
Adipose Tissue ◽  
Transgenic Mice ◽  
G Protein ◽  
Energy Status ◽  
Α Subunit ◽  
Fat Depots ◽  
Ucp1 Expression ◽  
White Fat ◽  
Stimulation Of

In vitro experiments suggest that stimulation of lipolysis by catecholamines in adipocytes depends on the energy status of these cells. We tested whether mitochondrial uncoupling proteins (UCPs) that control the efficiency of ATP production could affect lipolysis and noradrenaline signalling in white fat in vivo. The lipolytic effect of noradrenaline was lowered by ectopic UCP1 in white adipocytes of aP2-Ucp1 transgenic mice, overexpressing the UCP1 gene from the aP2 gene promoter, reflecting the magnitude of UCP1 expression, the impaired stimulation of cAMP levels by noradrenaline and the reduction of the ATP/ADP ratio in different fat depots. Thus only subcutaneous but not epididymal fat was affected. UCP1 also down-regulated the expression of hormone-sensitive lipase and lowered its activity, and altered the expression of trimeric G-proteins in adipocytes. The adipose tissue content of the stimulatory G-protein α subunit was increased while that of the inhibitory G-protein α subunits decreased in response to UCP1 expression. Our results support the idea that the energy status of cells, and the ATP/ADP ratio in particular, modulates the lipolytic effects of noradrenaline in adipose tissue in vivo. They also demonstrate changes at the G-protein level that tend to overcome the reduction of lipolysis when ATP level in adipocytes is low. Therefore, respiratory uncoupling may exert a broad effect on hormonal signalling in adipocytes.

scholarly journals Gain-of-function screen of α-transducin identifies an essential phenylalanine residue necessary for full effector activation

2018 ◽  
Vol 293 (46) ◽  
pp. 17941-17952 ◽  
Author(s):  
Shawn K. Milano ◽  
Chenyue Wang ◽  
Jon W. Erickson ◽  
Richard A. Cerione ◽  
Sekar Ramachandran
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Binding Sites ◽  
Effector Proteins ◽  
Α Subunit ◽  
Gtp Binding ◽  
Effector Activity ◽  
Α Subunits ◽  
Phenylalanine Residue ◽  
Stimulation Of

Two regions on the α subunits of heterotrimeric GTP-binding proteins (G-proteins), the Switch II/α2 helix (which changes conformation upon GDP–GTP exchange) and the α3 helix, have been shown to contain the binding sites for their effector proteins. However, how the binding of Gα subunits to their effector proteins is translated into the stimulation of effector activity is still poorly understood. Here, we took advantage of a reconstituted rhodopsin-coupled phototransduction system to address this question and identified a distinct surface and an essential residue on the α subunit of the G-protein transducin (αT) that is necessary to fully activate its effector enzyme, the cGMP phosphodiesterase (PDE). We started with a chimeric G-protein α subunit (αT*) comprising residues mainly from αT and a short stretch of residues from the Gi1 α subunit (αi1), which only weakly stimulates PDE activity. We then reinstated the αT residues by systematically replacing the corresponding αi1 residues within αT* with the aim of fully restoring PDE stimulatory activity. These experiments revealed that the αG/α4 loop and a phenylalanine residue at position 283 are essential for conferring the αT* subunit with full PDE stimulatory capability. We further demonstrated that this same region and amino acid within the α subunit of the Gs protein (αs) are necessary for full adenylyl cyclase activation. These findings highlight the importance of the αG/α4 loop and of an essential phenylalanine residue within this region on Gα subunits αT and αs as being pivotal for their selective and optimal stimulation of effector activity.

scholarly journals Analysis of agonist function at fusion proteins between the IP prostanoid receptor and cognate, unnatural and chimaeric G-proteins

1999 ◽  
Vol 342 (2) ◽  
pp. 457-463 ◽  
Author(s):  
Chee Wai FONG ◽  
Graeme MILLIGAN
Keyword(s):  
Fusion Protein ◽  
G Protein ◽  
G Proteins ◽  
Fusion Proteins ◽  
Hek293 Cells ◽  
Gtpase Activity ◽  
Prostanoid Receptor ◽  
Protein Activation ◽  
G Protein Activation ◽  
Stimulation Of

Direct measures of G-protein activation based on guanine nucleotide exchange and hydrolysis are frequently impossible to monitor for receptors which interact predominantly with Gsα. An isolated FLAG (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys)-epitope-tagged human IP prostanoid receptor and fusion proteins generated between this form of the receptor and the α subunits of its cognate G-protein Gs, Gi1, a G-protein which it fails to activate in co-expression studies, and a chimaeric Gi1-Gs6 (a form of Gi1 in which the C-terminal six amino acids were replaced with the equivalent sequence of Gs) were stably expressed in HEK293 cells. These were detected by [3H]ligand-binding studies and by immunoblotting with both an anti-FLAG antibody and with appropriate antisera to the G-proteins. Each construct displayed similar affinity to bind the agonist iloprost. Iloprost stimulated adenylate cyclase activity in clones expressing both IP prostanoid receptor and the IP prostanoid receptor-Gsα fusion protein, and both constructs were shown to interact with and activate endogenously expressed Gsα. Addition of iloprost to membranes of cells expressing the isolated receptor resulted in a small stimulation of high-affinity GTPase activity. Iloprost produced no stimulation of GTPase activity which could be attributed to the IP prostanoid receptor-Gi1α fusion. However, the fusion proteins containing either Gsα or Gi1-Gs6α produced substantially greater stimulation of GTPase activity than the isolated IP prostanoid receptor. Treatment of cells expressing the IP prostanoid receptor-Gi1-Gs6α fusion protein with a combination of cholera and pertussis toxins allowed direct measurement of agonist activation of the receptor-linked G-protein. Normalization of such results for levels of expression of the IP prostanoid receptor constructs demonstrated a 5-fold higher stimulation of GTPase activity when using the Gsα-containing fusion protein and a 9-fold improvement when using the fusion protein containing Gi1-Gs6α to detect G-protein activation compared with expression of the isolated receptor.

A Key Role for Transmembrane Prolines in Calcitonin Receptor-Like Receptor Agonist Binding and Signalling: Implications for Family B G-Protein-Coupled Receptors

2004 ◽  
Vol 67 (1) ◽  
pp. 20-31 ◽  
Author(s):  
Alex C. Conner ◽  
Debbie L. Hay ◽  
John Simms ◽  
Stephen G. Howitt ◽  
Marcus Schindler ◽  
...  
Keyword(s):  
G Protein ◽  
Receptor Agonist ◽  
G Protein Coupled Receptors ◽  
Calcitonin Receptor ◽  
Agonist Binding ◽  
G Protein Coupled

Abstract 517: Ubiquitylation of G Protein Coupled Receptor Kinase 4 (GRK4) Regulates its Localization and Abundance

Hypertension ◽  
2014 ◽  
Vol 64 (suppl_1) ◽  
Author(s):  
John J Gildea ◽  
Walid Omer ◽  
Dora Bigler Wang ◽  
Hanh Tran ◽  
Robin A Felder
Keyword(s):  
Fusion Protein ◽  
G Protein ◽  
Nuclear Localization ◽  
Nuclear Import ◽  
26S Proteasome ◽  
Receptor Kinase ◽  
G Protein Coupled Receptor ◽  
Fusion Construct ◽  
Expression Levels ◽  
G Protein Coupled

The dopamine-1 receptor (D 1 R) is responsible for regulating up to 60% of natriuresis in the kidney under sodium loaded conditions. G protein coupled receptor kinase type 4 (GRK4) phosphorylates the D 1 R and reduces its membrane expression, but little is known about regulation of GRK4. We hypothesized that GRK4 is targeted for elimination through ubiquitylation. Using D 1 R and GRK4γ stably transfected human embryonic kidney cells (HEK293), we demonstrated GRK4 and ubiquitin coimmunoprecipitation. Addition of clasto-lactacystin beta-lactone (CLBL, an inhibitor of the 26S proteasome) increased GRK4 expression levels (western blot) using two different GRK4 fusion protein constructs. The addition of CLBL (10 μmol/L, 24 hrs) increased the expression of both a tandem affinity tagged (tap-tag) GRK4 fusion construct (2.65±0.19 fold over vehicle (VEH): VEH 4,010±404 RFU; CLBL 10,626±744 RFU, P<0.05, N=3) as well as a mCherry GRK4 fusion construct (6.98±0.50 fold increase over VEH: VEH 5,044±3229 RFU; CLBL 35,210±2547 RFU, P<0.05, N=3). The ubiquitin binding sites (AA 216,217; MYACK Ub K Ub LQKK) are located near the nuclear localization signal (AA 219-228; QKKRIKKRK) in GRK4. We therefore examined the subcellular localization of GRK4 after CLBL treatment. Nuclear accumulation of the GRK4-mCherry fusion protein fluorescence decreased markedly while cytoplasmic GRK4-mCherry fluorescence increased (nuclear to cytoplasmic GRK4 ratio: VEH 1.18±0.09 RFU; CLBL 0.78±0.03 RFU, P<0.01, N=12). In summary, GRK4 expression levels are negatively regulated by the ubiquitin proteasome system and ubiquitylation of GRK4 prevents nuclear import. We hypothesize that ubiquitylation is sterically hindering the nuclear localization sequence in GRK4 from interacting with the nuclear import machinery of the cell. Through manipulation of GRK4 ubiquitylation, one may be able to separate nuclear vs. cytoplasmic activity of GRK4 and reverse the negative impact overactive GRK4 has on dopaminergic signaling.

scholarly journals Stimulation of Cholesterol Excretion by the Liver X Receptor Agonist Requires ATP-binding Cassette Transporters G5 and G8

2003 ◽  
Vol 278 (18) ◽  
pp. 15565-15570 ◽  
Author(s):  
Liqing Yu ◽  
Jennifer York ◽  
Klaus von Bergmann ◽  
Dieter Lutjohann ◽  
Jonathan C. Cohen ◽  
...  
Keyword(s):  
Receptor Agonist ◽  
Liver X Receptor ◽  
Atp Binding ◽  
Atp Binding Cassette Transporters ◽  
Cholesterol Excretion ◽  
Liver X Receptor Agonist ◽  
Stimulation Of ◽  
Atp Binding Cassette
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