Diversity among the beta subunits of heterotrimeric GTP-binding proteins: Characterization of a novel beta-subunit cDNA

doi:10.1016/0006-291X(92)91650-F

Biochemical and Biophysical Research Communications

Volume 183, Issue 1, 28 February 1992, Pages 350-356

https://doi.org/10.1016/0006-291X(92)91650-F Get rights and content

Abstract

Heterotrimeric guanine nucleotide binding proteins transduce signals from cell surface receptors to intracellular effectors. The alpha subunit is believed to confer receptor and effector specificity on the G protein. This role is reflected in the diversity of genes that encode these subunits. The beta and gamma subunits are thought to have a more passive role in G protein function; biochemical data suggests that beta-gamma dimers are shared among the alpha subunits. However, there is growing evidence for active participation of beta-gamma dimers in some G protein mediated signaling systems. To further investigate this role, we examined the diversity of the beta subunit family in mouse. Using the polymerase chain reaction, we uncovered a new member of this family, Gβ4, which is expressed at widely varying levels in a variety of tissues. The predicted amino acid sequence of Gβ4 is 79% to 89% identical to the three previously known beta subunits. The diversity of beta gene products may be an important corollary to the functional diversity of G proteins.

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Subtype-dependent regulation of Gβγ signalling
2021, Cellular Signalling
Citation Excerpt :
Compared to Gβ1 and Gβ2, Gβ4 expression widely varies in different tissues. Independent studies showed that Gβ4 is highly expressed in skin fibroblasts [90], brain, eye, heart, testis [54], lung, and placenta, while it is less abundant in the brain, spleen, and heart [91,92]. Mouse and human Gβ5 are predominantly expressed in the brain [45], whereas human Gβ5 is also abundant in the pancreas, kidney, and heart [47].
G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.
The human G protein β4 subunit: Gene structure, expression, Gγ and effector interaction
2003, FEBS Letters
The aim of this study was the characterization of the human Gβ4 subunit of heterotrimeric G proteins. Human Gβ4 is widely expressed. Its gene is located on chromosome 3 with a genomic structure indistinguishable from that of the genes of Gβ1 to Gβ3, but entirely different from Gβ5. In vitro translation co-precipitation analyses revealed that Gβ4 can form stable dimers with Gγ1, Gγ2, Gγ3, Gγ4, Gγ5, Gγ7, Gγ10, Gγ11, Gγ12, and Gγ13, dimers which were also able to stimulate phospholipase β2.
G Protein β Subunit Types Differentially Interact with a Muscarinic Receptor but Not Adenylyl Cyclase Type II or Phospholipase C-β2/3
2001, Journal of Biological Chemistry
In comparison with the α subunit of G proteins, the role of the β subunit in signaling is less well understood. During the regulation of effectors by the βγ complex, it is known that the β subunit contacts effectors directly, whereas the role of the β subunit is undefined in receptor-G protein interaction. Among the five G protein β subunits known, the β₄subunit type is the least studied. We compared the ability of βγ complexes containing β₄ and the well characterized β₁ to stimulate three different effectors: phospholipase C-β2, phospholipase C-β3, and adenylyl cyclase type II. β₄γ₂ and β₁γ₂ activated all three of these effectors with equal efficacy. However, nucleotide exchange in a G protein constituting α_oβ₄γ₂ was stimulated significantly more by the M2 muscarinic receptor compared with α_oβ₁γ₂. Because α_o forms heterotrimers with β₄γ₂ and β₁γ₂equally well, these results show that the β subunit type plays a direct role in the receptor activation of a G protein.
The G Protein β Subunit is a Determinant in the Coupling of G <inf>s</inf> to the β<inf>1</inf>-Adrenergic and A2a Adenosine Receptors
2001, Journal of Biological Chemistry
Citation Excerpt :
Baculoviruses encoding the rat β1-adrenergic receptor and the human A2a adenosine receptor were gifts from E. Ross (University of Texas, Southwestern Medical Center) and J. Linden (University of Virginia), respectively (29). The human β3 cDNA (30), a gift from S. R. Ikeda (Guthrie Institute), was excised from pCI with EcoRI and NotI; the mouse β4 cDNA (31), a gift from W. F. Simonds (National Institutes of Health) was excised from pcDNA3 with BamHI and XbaI. The human β3s cDNA, a gift from D. Rosskopf (Institute for Pharmacology, Essen, Germany), is a truncated variant of the full-length β3 cDNA, in which the β3s protein product has a deletion of amino acids 168–208 (32); excision of the β3s cDNA from pGEMT was accomplished withBamHI and PstI.
The signaling specificity of five purified G protein βγ dimers, β₁γ₂, β₂γ₂, β₃γ₂, β₄γ₂, and β₅γ₂, was explored by reconstituting them with G_s α and receptors or effectors in the adenylyl cyclase cascade. The ability of the five βγ dimers to support receptor-α-βγ interactions was examined using membranes expressing the β₁-adrenergic or A2a adenosine receptors. These receptors discriminated among the defined heterotrimers based solely on the β isoform. The β₄γ₂ dimer demonstrated the highest coupling efficiency to either receptor. The β₅γ₂ dimer coupled poorly to each receptor, with EC₅₀ values 40–200-fold higher than those observed with β₄γ₂. Strikingly, whereas the EC₅₀ of the β₁γ₂ dimer at the β₁-adrenergic receptor was similar to β₄γ₂, its EC₅₀ was 20-fold higher at the A2a adenosine receptor. Inhibition of adenylyl cyclase type I (AC1) and stimulation of type II (AC2) by the βγ dimers were measured. βγ dimers containing Gβ_1–4 were able to stimulate AC2 similarly, and β₅γ₂ was much less potent. β₁γ₂, β₂γ₂, and β₄γ₂inhibited AC1 equally; β₃γ₂ was 10-fold less effective, and β₅γ₂ had no effect. These data argue that the β isoform in the βγ dimer can determine the specificity of signaling at both receptors and effectors.
Stage-specific modification of G protein beta subunits in rat placenta
2001, Molecular and Cellular Endocrinology
We previously analysed the plasma membrane proteins of rat placenta and prepared a database of 150 plasma membrane proteins, expressed in a stage-specific manner, utilizing two-dimensional gel electrophoresis (2D/E) [Mol. Cell. Endocrinol. 115(1995)149]. In this study, we focused on the proteins, tentatively named psL-I (MW 36.2 kDa, pI 5.3) and psL-II (35.9 kDa, 5.3), which were expressed mainly in late pregnancy. Close to psL-I and psL-II on 2D/E gels, we also recognized more abundant proteins [psC-I (36.2 kDa, 5.4) and psC-II (35.9 kDa, 5.4), respectively] arranged side by side with the same MW but different pI. Expression of psL-I and psL-II was detected only in junctional zone of placenta, whereas psC-I and psC-II were expressed in both labyrinth and junctional zones. In addition, psL-I and psL-II began to increase on day 16 of pregnancy and peaked at term, whereas expression of psC-I and psC-II was relatively constant. The analysis of these four proteins (psL-I, psL-II, psC-I and psC-II) by preparative 2D/E, peptide mapping, amino acid sequence and mass spectrometry (MALDI-TOF-MS) revealed that psC-I was a G protein β1 subunit, and psC-II was a β2 subunit, and showed that psL-I and psL-II were molecular modified forms of psC-I and psC-II, respectively. Expression of these G protein β subunits (psL-I, psL-II, psC-I and psC-II) was also observed in rat choriocarcinoma cells, Rcho-1 cells. Expression of psC-I and psC-II was much higher than those of psL-I and psL-II, and their level was relatively constant regardless of the stage of differentiation in vitro. Interestingly, expression of psL-I and psL-II gradually increased in association with the differentiation. Since the expression of β1 and β2 subunit proteins and their mRNAs was constant during the process of differentiation in Rcho-1 cells, the expression of these lower pI forms of G protein subunits (psL-I and psL-II) was thought to be post-translationally regulated. In conclusion, there are modified forms of G protein β1 and β2 subunits, in the placenta and Rcho-1 cells, which are expressed in a pregnancy-stage or differentiation stage specific manner.
Two RGS proteins that inhibit Gα<inf>o</inf> and Gα<inf>q</inf> signaling in C. elegans neurons require a Gβ<inf>5</inf>-like subunit for function
2001, Current Biology
Citation Excerpt :
The signal transmitted through an activated G protein is terminated upon hydrolysis of bound GTP, returning the G protein to its inactive, heterotrimeric form. Five Gβ subunits have been identified in mammals [2–8]. The Gβ1 through Gβ4 proteins show a high degree of conservation and are ∼80% identical to one another at the amino acid level [5].
Background: Gβ proteins have traditionally been thought to complex with Gγ proteins to function as subunits of G protein heterotrimers. The divergent Gβ₅ protein, however, can bind either Gγ proteins or regulator of G protein signaling (RGS) proteins that contain a G gamma–like (GGL) domain. RGS proteins inhibit G protein signaling by acting as Gα GTPase activators. While Gβ₅ appears to bind RGS proteins in vivo, its association with Gγ proteins in vivo has not been clearly demonstrated. It is unclear how Gβ₅ might influence RGS activity. In C. elegans there are exactly two GGL-containing RGS proteins, EGL-10 and EAT-16, and they inhibit Gα_o and Gα_q signaling, respectively.
Results: We knocked out the gene encoding the C. elegans Gβ₅ ortholog, GPB-2, to determine its physiological roles in G protein signaling. The gpb-2 mutation reduces the functions of EGL-10 and EAT-16 to levels comparable to those found in egl-10 and eat-16 null mutants. gpb-2 knockout animals are viable, and exhibit no obvious defects beyond those that can be attributed to a reduction of EGL-10 or EAT-16 function. GPB-2 protein is nearly absent in eat-16; egl-10 double mutants, and EGL-10 protein is severely diminished in gpb-2 mutants.
Conclusions: Gβ₅ functions in vivo complexed with GGL-containing RGS proteins. In the absence of Gβ₅, these RGS proteins have little or no function. The formation of RGS–Gβ₅ complexes is required for the expression or stability of both the RGS and Gβ₅ proteins. Appropriate RGS–Gβ₅ complexes regulate both Gα_o and Gα_q proteins in vivo.

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Diversity among the beta subunits of heterotrimeric GTP-binding proteins: Characterization of a novel beta-subunit cDNA

Abstract

Cell

FEBS lett

J. Biol. chem

J. Biol. Chem

Cell

Cell

Science

Biochemistry

Ann. Rev. Biochem

Nature

Cell

Nature

Science