scholarly journals A G protein-gated K channel is activated via beta 2-adrenergic receptors and G beta gamma subunits in Xenopus oocytes.

1995 ◽  
Vol 105 (3) ◽  
pp. 421-439 ◽  
Author(s):  
N F Lim ◽  
N Dascal ◽  
C Labarca ◽  
N Davidson ◽  
H A Lester
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Xenopus Oocytes ◽  
K Channel ◽  
Intracellular Camp ◽  
Heterotrimeric G Proteins ◽  
M2 Muscarinic Receptor ◽  
Gamma Subunits ◽  
Beta 2 ◽  
Inwardly Rectifying

In many tissues, inwardly rectifying K channels are coupled to seven-helix receptors via the Gi/Go family of heterotrimeric G proteins. This activation proceeds at least partially via G beta gamma subunits. These experiments test the hypothesis that G beta gamma subunits activate the channel even if released from other classes of heterotrimeric G proteins. The G protein-gated K channel from rat atrium, KGA/GIRK1, was expressed in Xenopus oocytes with various receptors and G proteins. The beta 2-adrenergic receptor (beta 2AR), a Gs-linked receptor, activated large KGA currents when the alpha subunit, G alpha s, was also overexpressed. Although G alpha s augmented the coupling between beta 2AR and KGA, G alpha s also inhibited the basal, agonist-independent activity of KGA. KGA currents stimulated via beta 2AR activated, deactivated, and desensitized more slowly than currents stimulated via Gi/Go-linked receptors. There was partial occlusion between currents stimulated via beta 2AR and the m2 muscarinic receptor (a Gi/Go-linked receptor), indicating some convergence in the mechanism of activation by these two receptors. Although stimulation of beta 2AR also activates adenylyl cyclase and protein kinase A, activation of KGA via beta 2AR is not mediated by this second messenger pathway, because direct elevation of intracellular cAMP levels had no effect on KGA currents. Experiments with other coexpressed G protein alpha and beta gamma subunits showed that (a) a constitutively active G alpha s mutant did not suppress basal KGA currents and was only partially as effective as wild type G alpha s in coupling beta 2AR to KGA, and (b) beta gamma subunits increased basal KGA currents. These results reinforce present concepts that beta gamma subunits activate KGA, and also suggest that beta gamma subunits may provide a link between KGA and receptors not previously known to couple to inward rectifiers.

scholarly journals Production, processing and partial purification of functional G protein βγ subunits in baculovirus-infected insect cells

1992 ◽  
Vol 286 (3) ◽  
pp. 677-680 ◽  
Author(s):  
J D Robishaw ◽  
V K Kalman ◽  
K L Proulx
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Insect Cells ◽  
Expression System ◽  
Baculovirus Expression System ◽  
Partial Purification ◽  
Baculovirus Expression ◽  
Gamma Subunits ◽  
Infected Insect ◽  
Beta 2

As a result of the inability to resolve the heterogeneous mixture of G protein beta gamma subunits present in tissues, it has not been possible to compare different beta gamma subunits of the G proteins in terms of their proposed roles in receptor-effector coupling. This study was undertaken to establish the utility of the baculovirus expression system in producing homogeneous beta gamma subunits of defined composition for the comparative analysis of these subunits in reconstitution systems. In this study we report the expression, and appropriate post-translational processing, of recombinant beta 2, gamma 2 and gamma 3 subunits. In addition, we show that the recombinant beta gamma subunits can be readily purified, and can functionally interact with the alpha subunits of the G proteins.

scholarly journals Positive and Negative Coupling of the Metabotropic Glutamate Receptors to a G Protein–activated K+ Channel, GIRK, in Xenopus Oocytes

1997 ◽  
Vol 109 (4) ◽  
pp. 477-490 ◽  
Author(s):  
Dahlia Sharon ◽  
Dmitry Vorobiov ◽  
Nathan Dascal
Keyword(s):  
Protein Kinase ◽  
Glutamate Receptors ◽  
G Protein ◽  
G Proteins ◽  
Metabotropic Glutamate Receptors ◽  
Xenopus Oocytes ◽  
K Channel ◽  
Metabotropic Glutamate ◽  
Girk Channel ◽  
The Brain

Metabotropic glutamate receptors (mGluRs) control intracellular signaling cascades through activation of G proteins. The inwardly rectifying K+ channel, GIRK, is activated by the βγ subunits of Gi proteins and is widely expressed in the brain. We investigated whether an interaction between mGluRs and GIRK is possible, using Xenopus oocytes expressing mGluRs and a cardiac/brain subunit of GIRK, GIRK1, with or without another brain subunit, GIRK2. mGluRs known to inhibit adenylyl cyclase (types 2, 3, 4, 6, and 7) activated the GIRK channel. The strongest response was observed with mGluR2; it was inhibited by pertussis toxin (PTX). This is consistent with the activation of GIRK by Gi/Go-coupled receptors. In contrast, mGluR1a and mGluR5 receptors known to activate phospholipase C, presumably via G proteins of the Gq class, inhibited the channel's activity. The inhibition was preceded by an initial weak activation, which was more prominent at higher levels of mGluR1a expression. The inhibition of GIRK activity by mGluR1a was suppressed by a broad-specificity protein kinase inhibitor, staurosporine, and by a specific protein kinase C (PKC) inhibitor, bis-indolylmaleimide, but not by PTX, Ca2+ chelation, or calphostin C. Thus, mGluR1a inhibits the GIRK channel primarily via a pathway involving activation of a PTX-insensitive G protein and, eventually, of a subtype of PKC, possibly PKC-μ. In contrast, the initial activation of GIRK1 caused by mGluR1a was suppressed by PTX but not by the protein kinase inhibitors. Thus, this activation probably results from a promiscuous coupling of mGluR1a to a Gi/Go protein. The observed modulations may be involved in the mGluRs' effects on neuronal excitability in the brain. Inhibition of GIRK by phospholipase C–activating mGluRs bears upon the problem of specificity of G protein (GIRK interaction) helping to explain why receptors coupled to Gq are inefficient in activating GIRK.

Muscarine-gated K+ channel: subunit stoichiometry and structural domains essential for G protein stimulation

1996 ◽  
Vol 271 (1) ◽  
pp. H379-H385 ◽  
Author(s):  
S. J. Tucker ◽  
M. Pessia ◽  
J. P. Adelman
Keyword(s):  
G Protein ◽  
Xenopus Oocytes ◽  
K Channel ◽  
Channel Activity ◽  
Atrial Myocytes ◽  
Structural Domains ◽  
Maximal Stimulation ◽  
Subunit Stoichiometry ◽  
K Current ◽  
Inwardly Rectifying

Coexpression in Xenopus oocytes of the cloned cardiac inward rectifier subunits Kir 3.1 and Kir 3.4 results in G protein-stimulated channel activity closely resembling the muscarinic channel underlying the inwardly rectifying K+ current in atrial myocytes. To determine the stoichiometry and relative subunit positions within the channel, Kir 3.1 and Kir 3.4 were coexpressed in varying ratios with cloned G beta 1 gamma 2 subunits and also as tandemly linked tetramers with different relative subunit positions. The results reveal that the most efficient channel comprises two subunits of each type in an alternating array within the tetramer. To localize regions important for subunit coassembly and G protein sensitivity, chimeric subunits containing domains from either Kir 3.1, Kir 3.4, or the G protein-insensitive subunit Kir 4.1 were expressed. The results demonstrate that the transmembrane domains dictate the potentiation of the coassembled channels and that, although the NH4- or COOH-termini of both subunits alone can confer G protein sensitivity, both termini are required for maximal stimulation by G beta 1 gamma 2.

scholarly journals Localization of a heterotrimeric G protein gamma subunit to focal adhesions and associated stress fibers.

1994 ◽  
Vol 126 (3) ◽  
pp. 811-819 ◽  
Author(s):  
C A Hansen ◽  
A G Schroering ◽  
D J Carey ◽  
J D Robishaw
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Focal Adhesion ◽  
Cardiac Fibroblasts ◽  
Focal Adhesions ◽  
Heterotrimeric G Proteins ◽  
Gamma Subunit ◽  
Surface Receptors ◽  
Gamma Subunits ◽  
Dual Staining

Signal transducing heterotrimeric G proteins are responsible for coupling a large number of cell surface receptors to the appropriate effector(s). Of the three subunits, 16 alpha, 4 beta, and 5 gamma subunits have been characterized, indicating a potential for over 300 unique combinations of heterotrimeric G proteins. To begin deciphering the unique G protein combinations that couple specific receptors with effectors, we examined the subcellular localization of the gamma subunits. Using anti-peptide antibodies specific for each of the known gamma subunits, neonatal cardiac fibroblasts were screened by standard immunocytochemistry. The anti-gamma 5 subunit antibody yielded a highly distinctive pattern of intensely fluorescent regions near the periphery of the cell that tended to protrude into the cell in a fibrous pattern. Dual staining with anti-vinculin antibody showed co-localization of the gamma 5 subunit with vinculin. In addition, the gamma 5 subunit staining extended a short distance out from the vinculin pattern along the protruding stress fiber, as revealed by double staining with phalloidin. These data indicated that the gamma 5 subunit was localized to areas of focal adhesion. Dual staining of rat aortic smooth muscle cells and Schwann cells also indicated co-localization of the gamma 5 subunit and vinculin, suggesting that the association of the gamma 5 subunit with areas of focal adhesion was wide-spread.

Effects of ginsenoside on G protein-coupled inwardly rectifying K+ channel activity expressed in Xenopus oocytes

2003 ◽  
Vol 468 (2) ◽  
pp. 83-92 ◽  
Author(s):  
Seok Choi ◽  
Jun-Ho Lee ◽  
Yang In Kim ◽  
Man-Jong Kang ◽  
Hyewon Rhim ◽  
...  
Keyword(s):  
G Protein ◽  
Xenopus Oocytes ◽  
K Channel ◽  
Channel Activity ◽  
Inwardly Rectifying ◽  
G Protein Coupled

scholarly journals Olfactory desensitization requires membrane targeting of receptor kinase mediated by beta gamma-subunits of heterotrimeric G proteins.

1994 ◽  
Vol 269 (1) ◽  
pp. 37-40
Author(s):  
I. Boekhoff ◽  
J. Inglese ◽  
S. Schleicher ◽  
W.J. Koch ◽  
R.J. Lefkowitz ◽  
...  
Keyword(s):  
G Proteins ◽  
Membrane Targeting ◽  
Heterotrimeric G Proteins ◽  
Receptor Kinase ◽  
Gamma Subunits

scholarly journals Every Detail Matters. That Is, How the Interaction between Gα Proteins and Membrane Affects Their Function

Membranes ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 222
Author(s):  
Agnieszka Polit ◽  
Paweł Mystek ◽  
Ewa Błasiak
Keyword(s):  
Signal Transduction ◽  
G Protein ◽  
G Proteins ◽  
Lipid Membranes ◽  
Signaling Proteins ◽  
Heterotrimeric G Proteins ◽  
Membrane Attachment ◽  
The Individual ◽  
Multicellular Organisms ◽  
G Protein Coupled

In highly organized multicellular organisms such as humans, the functions of an individual cell are dependent on signal transduction through G protein-coupled receptors (GPCRs) and subsequently heterotrimeric G proteins. As most of the elements belonging to the signal transduction system are bound to lipid membranes, researchers are showing increasing interest in studying the accompanying protein–lipid interactions, which have been demonstrated to not only provide the environment but also regulate proper and efficient signal transduction. The mode of interaction between the cell membrane and G proteins is well known. Despite this, the recognition mechanisms at the molecular level and how the individual G protein-membrane attachment signals are interrelated in the process of the complex control of membrane targeting of G proteins remain unelucidated. This review focuses on the mechanisms by which mammalian Gα subunits of G proteins interact with lipids and the factors responsible for the specificity of membrane association. We summarize recent data on how these signaling proteins are precisely targeted to a specific site in the membrane region by introducing well-defined modifications as well as through the presence of polybasic regions within these proteins and interactions with other components of the heterocomplex.

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