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evolution
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expression of four Galpha, four Gbeta, and two Ggamma proteins, expression profiles by quantitative PCR, the four Galpha proteins form two distinct groups based on their GTPase activity. The proteins interact in most of the possible combinations, with some degree of interaction specificity between duplicated gene pairs
evolution
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Galpha subunits are classified into four subfamilies, Gs, Gi, Gq and G12. Galpha12/13 and Galphaq are directly involved in the activation of RhoGTPases, molecular mechanisms for regulation of RhoGTPase activity through GPCR heterotrimeric G12/13-signalling pathways, overview. The G12/13-RH-RhoGEF signalling mechanism is well conserved over species
evolution
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Galpha subunits are classified into four subfamilies, Gs, Gi, Gq and G12. Galpha12/13 and Galphaq are directly involved in the activation of RhoGTPases, molecular mechanisms for regulation of RhoGTPase activity through GPCR heterotrimeric G12/13-signalling pathways, overview. The G12/13-RH-RhoGEF signalling mechanism is well conserved over species
evolution
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Galpha subunits are classified into four subfamilies, Gs, Gi, Gq and G12. Galpha12/13 and Galphaq are directly involved in the activation of RhoGTPases, molecular mechanisms for regulation of RhoGTPase activity through GPCR heterotrimeric G12/13-signalling pathways, overview. The G12/13-RH-RhoGEF signalling mechanism is well conserved over species
evolution
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phylogenetic comparison of genes involved in the heterotrimeric G-proteins signaling system, detailed overview over eukaryotic lineages and structural similarities. Identification of heterotrimeric G-protein subunits, RGS domain proteins and 7TM receptors. Through much of eukaryotic evolution, cells contain both 7TM receptors that acted as GEFs and those as GAPs (with C-terminal RGS domains) for Galphas
evolution
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plants also possess relatively fewer G-protein subunits when compared with the mammalian systems. A highly elaborated plant G-protein network is present in soybean where recent genome duplication has led to existence of 4 Galpha, 4 Gbeta, 12 Ggamma, and 2 RGS proteins
evolution
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the core G-protein components and their activation/deactivation chemistries are broadly conserved throughout the eukaryotic evolution, while their regulatory mechanisms seem to have been rewired in plants to meet specific needs. Plants such as Arabidopsis, which have a limited number of G-protein components and their regulators, offer a unique opportunity to dissect the mechanistic details of distinct signaling pathways
malfunction
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deletion of any component of the Galpha13-RhoGEF-RhoA-signalling pathway results in a similar phenotype consisting of embryonic lethality at the stage of gastrulation
malfunction
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overexpression of constitutively active Galpha12 or 13 induces several cellular effects which suggest stimulation of Rho activity in cells, such as formation of actin stress fibres or neurite retraction in neuronal cells. NIH3T3 transforming activity of constitutively active mutant of Galpha12 can be prevented by blocking its palmitoylation
malfunction
Q05425; Q05424; Q9HFW7
none of the activated Galpha alleles restore female fertility to DELTAgnb-1 mutants, and the gna-3Q208L allele inhibits formation of female reproductive structures, consistent with a need for Galpha proteins to cycle through the inactive GDP-bound form for these processes. During the sexual cycle, DELTAgnb-1 and DELTAgna-1 mutants are male fertile but female sterile, Although these strains produce protoperithecia and trichogynes, their trichogynes have a defect in chemotropism and are not attracted by male cells. DELTAgna-2 and DELTAgna-3 mutants produce protoperithecia and develop perithecia after fertilization with wild-type males. Mutant phenotypes during asexual growth and development, overview
malfunction
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decreased expression of Gbeta and group I Ggamma genes leads to a significant decrease in nodule number, whereas the converse is true for the overexpression of specific Gbeta and Ggamma genes. Changing the availability of free, active Galpha proteins by modulating the level of the regulatory RGS proteins results in significantly altered nodule numbers. Overexpression of mutant Galpha1Q223L and Galpha1G196S, as confirmed by evaluating the transcript level of the transformed genes, results in a significant decrease in nodule number per transformed root
malfunction
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none of the activated Galpha alleles restore female fertility to DELTAgnb-1 mutants, and the gna-3Q208L allele inhibits formation of female reproductive structures, consistent with a need for Galpha proteins to cycle through the inactive GDP-bound form for these processes. During the sexual cycle, DELTAgnb-1 and DELTAgna-1 mutants are male fertile but female sterile, Although these strains produce protoperithecia and trichogynes, their trichogynes have a defect in chemotropism and are not attracted by male cells. DELTAgna-2 and DELTAgna-3 mutants produce protoperithecia and develop perithecia after fertilization with wild-type males. Mutant phenotypes during asexual growth and development, overview
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metabolism
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complex regulation of the G-protein cycle in soybean and in other plants with expanded G-protein networks
metabolism
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the Galpha proteins form an elaborate heterotrimeric G-protein network
metabolism
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the interaction network of rhodopsin involving the heterotrimeric G-protein transducin and the monomeric GTPase Rac1 is determined by distinct binding processes, association of transducin and rhodopsin occurs with higher affinity and speed than the binding of Rac1 to rhodopsin. In dark-adapted rod cells, Rac1 cannot compete with transducin for binding to rhodopsin, and signalling can proceed normally. The concentration of transducin has to drop significantly so that Rac1 can bind to rhodopsin, in the outer segment, this occurs only under intense illumination, when transducin is translocated to the inner segment
metabolism
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efficient activation and deactivation of Galpha protein is critical for the regulation of heterotrimeric G-protein mediated signaling pathways. Plants such as Arabidopsis, which have a limited number of G-protein components and their regulators, offer a unique opportunity to dissect the mechanistic details of distinct signaling pathways. Interaction occurs between the regulator of G-protein signaling 1 (RGS1) and phospholipase Dalpha1 (PLDalpha1), which are two of the GTPase activity accelerating proteins (GAPs) of the Arabidopsis Galpha protein, GPA1. Phosphatidic acid (PA), a key product of phospholipase Dalpha1 (PLDalpha1) activity, can bind with and modulate the GAP activity of RGS1, uncovering a molecular link between lipid and G-protein signaling and its role in providing the specificity of response regulation. Heterotrimeric G-protein signaling mechanisms and regulation, G-protein signaling model, overview
metabolism
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Rho guanine nucleotide exchange factor p63RhoGEF619 relocates to the plasma membrane upon activation of Galphaq coupled GPCRs, resembling the well-known activation mechanism of Rho guanine nucleotide exchange factors (RhoGEFs) activated by Galpha12/13. Synthetic recruitment of p63RhoGEF619 to the plasma membrane increases RhoGEF activity towards GTPase RhoA, but full activation requires allosteric activation via Galphaq, overview. Dual role for heterotrimeric G-protein Galphaq in RhoGEF activation, as it both recruits and allosterically activates cytosolic ARHGEF25 gene encoding three RhoGEF isoforms. Activation of the heterotrimeric G-protein Galphaq relieves the DH domain of p63RhoGEF from its autoinhibited state by allosteric interaction with the PH domain
metabolism
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Ric-8A controls cell polarization during migration probably through Galpha subunit regulation. Ric-8A by its two function as GEF and chaperone may regulate cell polarity by regulating the localization of proteins, such as Galpha-GDP, GPR1/GPR2 and Lin-5, during asymmetric cell division. Therefore in the context of migration it may also interact with a Galpha subunit, and its downstream effectors regulating aPKC and Par3 localization, then under Ric-8A morphant condition, the localization of these proteins is abnormal. Because GTPases regulate each other, any misregulation in one can result in abnormal regulation in the others
metabolism
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signaling pathways mediated by heterotrimeric G-protein complexes comprising Galpha, Gbeta, and Ggamma subunits and their regulatory RGS (regulator of G-protein signaling) protein are conserved in all eukaryotes. In soybean, phosphorylation-dependent regulation of G-protein cycle during nodule formation exists involving Nod factor receptor 1 (NFR1). The specific Gbeta and Ggamma proteins of a soybean heterotrimeric G-protein complex are involved in regulation of nodulation. During nodulation, the G-protein cycle is regulated by the activity of RGS proteins. Lower or higher expression of RGS proteins results in fewer or more nodules, respectively. NFR1 interacts with RGS proteins and phosphorylates them. Analysis of phosphorylated RGS protein identifies specific amino acids that, when phosphorylated, result in significantly higher GTPase accelerating activity. Active NFR1 receptors phosphorylate and activate RGS proteins, which help maintain the Galpha proteins in their inactive, trimeric conformation, resulting in successful nodule development. Alternatively, RGS proteins might also have a direct role in regulating nodulation because overexpression of their phospho-mimic version leads to partial restoration of nodule formation in nod49 mutants. The RGS proteins directly interact with, and are phosphorylated by, the NFR1 proteins. Phosphorylation of RGS proteins has important physiological consequences as overexpression of phospho-dead or phospho-mimic versions of RGS proteins results in a significant effect on nodule formation. The RGS protein-mediated acceleration of GTP hydrolysis is proposed to be the key regulatory step of plant G-protein signaling in contrast to mammalian systems where the GDP/GTP exchange mediated by the GPCRs is the rate-limiting step of the G-protein cycle. RGS proteins affect nodulation, they are positive regulators of nodule formation, detailed overview
physiological function
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Galpha proteins regulate G-protein signaling working with RGS proteins
physiological function
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the G12/13-RH-RhoGEF signalling mechanism is involved in critical steps for cell physiology and disease conditions, including embryonic development, oncogenesis and cancer metastasis. alpha Subunits of G12 or G13 interact with members of the RH domain containing guanine nucleotide exchange factors for Rho (RH-RhoGEF) family of proteins to directly connect G protein-mediated signalling and RhoGTPase signalling, G12/13-mediated signalling is one mechanism to regulate RhoGTPase activity in response to extracellular stimuli. Wild-type Galpha12 is the only Galpha subunit that acts as an oncogene in NIH3T3 cells
physiological function
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the G12/13-RH-RhoGEF signalling mechanism is involved in critical steps for cell physiology and disease conditions. alpha Subunits of G12 or G13 interact with members of the RH domain containing guanine nucleotide exchange factors for Rho (RH-RhoGEF) family of proteins to directly connect G protein-mediated signalling and RhoGTPase signalling, G12/13-mediated signalling is one mechanism to regulate RhoGTPase activity in response to extracellular stimuli
physiological function
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the G12/13-RH-RhoGEF signalling mechanism is involved in critical steps for cell physiology and disease conditions. alpha Subunits of G12 or G13 interact with members of the RH domain containing guanine nucleotide exchange factors for Rho (RH-RhoGEF) family of proteins to directly connect G protein-mediated signalling and RhoGTPase signalling, G12/13-mediated signalling is one mechanism to regulate RhoGTPase activity in response to extracellular stimuli
physiological function
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the virulence factor and highly potent mitogen Pasteurella multocida toxin, PMT, exhibits its toxic activity through activation of heterotrimeric GTPase-dependent pathways, by deamidating a glutamine residue in the alpha subunit of these GTPases via its C-terminal C3 domain, mechanism, overview. Galpha11 and Galphaq are substrates for PMT. C-PMT deamidates Galphaq at least tenfold more efficiently than the full-length PMT. Mutant PMT C1165S is not active on the GTPases, while the mutant C-terminal part of PMT C1159S deamidates Gai/q
physiological function
G-protein, Galpha16, is a critical downstream effector of non-canonical Wnt signaling and a potent inhibitor of transformed cell growth in non small cell lung cancer, Wnt7a-stimulated ERK5 activation is Galpha16-dependent. Importance of Wnt7a signaling via its cognate receptor Frizzled9, a G-protein-coupled receptor, in inhibition of cell proliferation, anchorage-independent growth, and reversal of transformed phenotype in non small cell lung cancer primarily through activation of the tumor suppressor, PPARgamma. Galpha16 is a regulator of non small cell lung cancer cell proliferation and anchorage-independent cell growth. Galpha16 and Galphaq are important mediators of PPARgamma and E-cadherin expression in non small cell lung cancer cell lines
physiological function
Q05425; Q05424; Q9HFW7
heterotrimeric G proteins are critical regulators of growth and asexual and sexual development in the filamentous fungus Neurospora crassa, wild-type phenotype during asexual growth and development
physiological function
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heterotrimeric G-proteins are important signal transducers in all eukaryotes. The protein complex consists of three dissimilar subunits: Galpha, Gbeta and Ggamma. The Galpha subunit is the enzymatically active protein of the complex which can exist in GTP-bound monomeric or GDP-bound trimeric conformation. The switch-like signaling mechanism has two distinct regulatory steps: the rate of GDP-GTP exchange facilitated by a cognate GPCR, which involves GDP release and GTP binding; and the rate of GTP hydrolysis by the Galpha protein. Two chimeric RGS proteins in soybean increase the rate of GTP hydrolysis by Galpha proteins and essentially regulate the duration of active signaling, they function primarily as GTPase accelerating proteins
physiological function
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in plants, heterotrimeric G-protein complexes play important roles in signal transduction pathways related to growth and development including response to biotic and abiotic stresses and consequently affect yield of crop plants
physiological function
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possible involvement of heterotrimeric G-protein signaling in Al-induced secretion of organic acid anions in Arabidopsis. Secretion of organic acid anions from the roots in response to aluminum is a common mechanism for Al resistance in plants
physiological function
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possible involvement of heterotrimeric G-protein signaling in Al-induced secretion of organic acid anions in rye. Secretion of organic acid anions from the roots in response to aluminum is a common mechanism for Al resistance in plants
physiological function
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a highly elaborated plant G-protein network is present in soybean where recent genome duplication has led to existence of 4 Galpha, 4 Gbeta, 12 Ggamma, and 2 RGS proteins. G-proteins from soybean have a direct negative role in signaling during nodulation. The Galpha proteins interact with the Nod factor receptors NFR1alpha and NFR1beta. The RGS protein-mediated acceleration of GTP hydrolysis is proposed to be the key regulatory step of plant G-protein signaling in contrast to mammalian systems where the GDP/GTP exchange mediated by the GPCRs is the rate-limiting step of the G-protein cycle
physiological function
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efficient activation and deactivation of Galpha protein is critical for the regulation of heterotrimeric G-protein mediated signaling pathways. Heterotrimeric GTP-binding proteins (G-proteins) are key regulators of a multitude of signaling pathways in all eukaryotes. In plants, G-proteins are currently a focus of intense research due to their involvement in modulation of many agronomically important traits such as abscisic acid-dependent signaling and stress responses, plant defense responses, seed yield, organ size, symbiosis and nitrogen use efficiency. Heterotrimeric G-protein signaling mechanisms and regulation, overview. GTPase activity accelerating proteins (GAPs) are required to increase the rate of deactivation, and to maintain the kinetics of G-protein cycle. Direct role of ABA-dependent phosphatidic acid production in the regulation of G-protein cycle during seed germination and primary root growth
physiological function
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heterotrimeric G proteins control cell migration in a variety of cellular types, also during embryogenesis. Four of the five Galpha subunit family members (Galpha12/13, Galphai/o, Galpha/11, and Galphas) are related to migration, activating different signaling cascades and promoting actin cytoskeleton reorganization through the regulation of small GTPase family proteins. The canonical cycle of heterotrimeric G protein signaling begins when a ligand binds to its receptor, which acts as a GEF and induces the activation of Galpha subunits and release from Gbetagamma by the exchange of GDP by GTP. In addition, some GEFs are ligand-independent, such as Ric-8, which accelerates the exchange of GDP for GTP on the Galpha subunit, thereby maintaining an active signaling state. The levels of Ric-8A are critical during migration and affect the localization of polarity markers and the subcellular localization of GTPase activity, suggesting that Ric-8A, probably through heterotrimeric G-protein signaling, regulates cell polarity during CNC migration, overview
physiological function
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possible involvement of heterotrimeric G-protein signaling in Al-induced secretion of organic acid anions in Arabidopsis. Secretion of organic acid anions from the roots in response to aluminum is a common mechanism for Al resistance in plants
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physiological function
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heterotrimeric G proteins are critical regulators of growth and asexual and sexual development in the filamentous fungus Neurospora crassa, wild-type phenotype during asexual growth and development
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additional information
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Gbetagamma interacts with the N-terminal alpha helix of Galpha through one of the seven bladed propellers of the Gbeta subunit
additional information
Q05425; Q05424; Q9HFW7
relationship between the three Galpha subunits and components of the Gbetagamma dimer, physical interaction between the Gbeta and Ggamma subunits, overview
additional information
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the complete heterotrimeric G-protein repertoire in the Capsicum annuum genome consists of one Galpha, one Gbeta and three Ggamma genes
additional information
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the core G-protein heterotrimeric complex consists of one Glphaa, one Gbeta, and one Ggamma protein. The protein complex switches between the inactive and active states depending on the nucleotide- bound form of Galpha. During resting phase, Galpha is GDP-bound and remains associated with the Gbetagamma proteins in a trimeric conformation (GDP-Galphabetagamma). Activation occurs due to the signal-dependent exchange of GDP on Galpha for GTP. GTP-bound Galpha dissociates from the Gbetagamma dimer and both GTP-Galpha and Gbetagamma can interact with downstream effectors to transduce the signal. Deactivation occurs via the inherent GTPase activity of Galpha, which causes hydrolysis of bound GTP, to produce its GDP-bound form. GDP-Galpha reassociates with Gbetagamma generating the trimeric complex, ready to be activated for the next round of signaling
additional information
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relationship between the three Galpha subunits and components of the Gbetagamma dimer, physical interaction between the Gbeta and Ggamma subunits, overview
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