A Novel Form of the G Protein β Subunit Gβ5 Is Specifically Expressed in the Vertebrate Retina

Watson, Angela; Aragay, Anna M.; Slepak, Vladlen Z.; Simon, Melvin I.

doi:10.1074/jbc.271.45.28154

Cited by 131 publications

(122 citation statements)

References 34 publications

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“…1C). This molecular mass corresponds to that of G ␤5L (43,566 Da in mouse), which was previously reported to be a ROS-specific, membrane-associated protein of unknown function (25). To test the hypothesis that the 44-kDa protein is G ␤5L , we generated three different antibodies against peptides from various regions of G ␤5L , including the N-terminal sequence which is absent in the G ␤5 short splice variant.…”

Section: Resultsmentioning

confidence: 96%

The GTPase activating factor for transducin in rod photoreceptors is the complex between RGS9 and type 5 G protein β subunit

Makino

Handy

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

200

134

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Proteins of the regulators of G protein signaling (RGS) family modulate the duration of intracellular signaling by stimulating the GTPase activity of G protein ␣ subunits. It has been established that the ninth member of the RGS family (RGS9) participates in accelerating the GTPase activity of the photoreceptor-specific G protein, transducin. This process is essential for timely inactivation of the phototransduction cascade during the recovery from a photoresponse. Here we report that functionally active RGS9 from vertebrate photoreceptors exists as a tight complex with the long splice variant of the G protein ␤ subunit (G ␤5L ). RGS9 and G ␤5L also form a complex when coexpressed in cell culture. Our data are consistent with the recent observation that several RGS proteins, including RGS9, contain G protein ␥-subunit like domain that can mediate their association with G ␤5 ( Heterotrimeric G proteins act as molecular switches that relay excitation from activated receptors to effector molecules, such as enzymes or ion channels. A G protein becomes activated upon the receptor-stimulated binding of GTP to its ␣ subunit and continues to modulate the activity of the effector until bound GTP is hydrolyzed (reviewed in refs. 1 and 2). In many signaling pathways, the duration of the signal under physiological conditions is much shorter than would be predicted from the intrinsic rate of ␣ subunits of G proteins (G ␣ ) GTPase activity. This is because GTPase activities of many G ␣ s are dramatically accelerated by RGS (regulators of G protein signaling) proteins or by the G protein effectors (reviewed in refs. 3-6). The phototransduction cascade of vertebrate photoreceptors represents one of the most sophisticated examples of such regulation where the GTPase activity of the G protein, transducin, is substantially enhanced by the cooperative action of RGS9 and the ␥ subunit of the effector of transducin, cGMP phosphodiesterase (PDE ␥ ) (7-10). The role of RGS9 is to provide transducin with the RGS homology domain, which acts catalytically in stimulating the rate of transducin GTPase. PDE ␥ itself does not activate transducin GTPase but it enhances the catalytic action of RGS9. The degree of this potentiation observed in physiologically intact photoreceptors is Ϸ7-fold (10). We believe that this ability of PDE ␥ to potentiate RGS9 action is essential for photoreceptor function. When a rod photoreceptor is hit by photon of light it has to perform two tasks. First, it has to transmit the signal from excited rhodopsin to PDE with high efficiency. Second, it has to inactivate all activated proteins in the cascade, including transducin, within a fraction of 1 s. If transducin is allowed to be discharged by RGS9 before it forms a complex with PDE, then some transducin molecules would never activate PDE and signal amplification would be diminished. Therefore, making the GTPase activation contingent on transducin association with PDE ␥ ensures both high efficiency of signal transmission between transducin and PDE and timel...

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Section: Resultsmentioning

confidence: 96%

The GTPase activating factor for transducin in rod photoreceptors is the complex between RGS9 and type 5 G protein β subunit

Makino

Handy

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

200

134

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“…The baculovirus expression construct encoding G␤5L employed the mouse cDNAs ligated between the EcoRI and XbaI cloning sites in pVL1392. G␤5L was modified by a M43L point mutation to block an internal translation initiation site (22).…”

Section: Methodsmentioning

confidence: 99%

Noncatalytic Domains of RGS9-1·Gβ5L Play a Decisive Role in Establishing Its Substrate Specificity

Martemyanov

Arshavsky

2002

Journal of Biological Chemistry

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The complex between the photoreceptor-specific regulator of G protein signaling (RGS) protein, RGS9-1, and type 5 G protein ␤-subunit, G␤5L, regulates the duration of the cellular response to light by stimulating the GTPase activity of G protein, transducin. An important property of RGS9-1⅐G␤5L is that it interacts specifically with transducin bound to its effector, cGMP phosphodiesterase, rather than with transducin alone. The minimal structure within the RGS9-1⅐G␤5L complex capable of activating transducin GTPase is the catalytic domain of RGS9. This domain itself is also able to discriminate between free and effector-bound transducin but to a lesser degree than RGS9-1⅐G␤5L. The goal of this study was to determine whether other, noncatalytic domains of RGS9-1⅐G␤5L enhance the intrinsic specificity of the catalytic domain or whether they set the specificity of RGS9-1⅐G␤5L regardless of the specificity of its catalytic domain. We found that a double L353E/R360P amino acid substitution reversed the specificity of the recombinant catalytic domain but did not reverse the specificity of RGS9-1⅐G␤5L. However, the degree of discrimination between free and effector-bound transducin was reduced. Therefore, noncatalytic domains of RGS9-1⅐G␤5L play a decisive role in establishing its substrate specificity, yet the high degree of this specificity observed under physiological conditions requires an additional contribution from the catalytic domain.RGS 1 proteins regulate the duration of signaling in many G protein pathways (1-3). They act by stimulating the GTP hydrolysis on G protein ␣-subunits, which results in termination of signaling events conferred by activated G proteins. All RGS proteins share a conservative catalytic domain of ϳ130 amino acid residues capable of accelerating the GTP hydrolysis on G protein ␣-subunits (2). Many RGS proteins are also equipped with other, noncatalytic domains (3). There are indications that these noncatalytic domains may participate in modulation of the RGS catalytic activity or may allow RGS proteins to interact with components of other intracellular pathways (reviewed in Ref. 4).Another putative role for the noncatalytic domains of RGS proteins is to contribute to the recognition of their specific G protein ␣-subunit targets. The idea that noncatalytic domains of RGS proteins may contribute to establishing the specificity in the RGS-G protein interactions is supported by several recent observations (5-7). Understanding the molecular mechanisms conferring this specificity has been complicated by many reports that RGS proteins and especially their catalytic domains can stimulate the GTPase activity of a broad spectrum of G protein ␣-subunits in vitro.The phototransduction cascade from vertebrate photoreceptors provides a useful model for studying substrate specificity in RGS proteins. In this cascade, the complex between the short splice isoform of RGS9 (RGS9-1) and the long splice isoform of type 5 G protein ␤-subunit (G␤5L) stimulates the GTPase activity of G protein, transducin (G ...

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“…Five distinct bsubunits referred as b1, b2, b3, b4 and b5 have been identi®ed (Clapham and Neer, 1993;Watson et al, 1994Watson et al, , 1996. While b1, b2, b3, b4 are ubiquitously expressed, b5 appears to have tissue-speci®c expres-sions present only in the retina, neuronal tissue, and platelets.…”

Section: Diversity Of G Protein Signalingmentioning

confidence: 99%

Regulation of cell proliferation by G proteins

Dhanasekaran

Tsim²,

Dermott³

et al. 1998

Oncogene

136

107

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G Proteins provide signal transduction mechanisms to seven transmembrane receptors. Recent studies have indicated that the a-subunits as well as the bg-subunits of these proteins regulate several critical signaling pathways involved in cell proliferation, di erentiation and apoptosis. Of the 17 a-subunits that have been cloned, at least ten of them have been shown to couple mitogenic signaling in ®broblast cells. Activating mutations in Ga s , Ga i2 , and Ga 12 have been correlated with di erent types of tumors. In addition, the ability of the bg-subunits to activate mitogenic pathways in di erent cell-types has been de®ned. The present review brie¯y summarizes the diverse and novel signaling pathways regulated by the a-as well as the bg-subunits of G proteins in regulating cell proliferation.

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A Novel Form of the G Protein β Subunit Gβ5 Is Specifically Expressed in the Vertebrate Retina

Cited by 131 publications

References 34 publications

The GTPase activating factor for transducin in rod photoreceptors is the complex between RGS9 and type 5 G protein β subunit

The GTPase activating factor for transducin in rod photoreceptors is the complex between RGS9 and type 5 G protein β subunit

Noncatalytic Domains of RGS9-1·Gβ5L Play a Decisive Role in Establishing Its Substrate Specificity

Regulation of cell proliferation by G proteins

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