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Showing papers on "GTP-Binding Protein alpha Subunits published in 2001"


Journal ArticleDOI
15 Jun 2001-Science
TL;DR: Results from loss of function and ectopic expression and activation of GPA1 indicate that this subunit is a positive modulator of cell division in plants.
Abstract: The alpha subunit of a prototypical heterotrimeric GTP-binding protein (G protein), which is encoded by a single gene (GPA1) in Arabidopsis, is a modulator of plant cell proliferation. gpa1 null mutants have reduced cell division in aerial tissues throughout development. Inducible overexpression of GPA1 in Arabidopsis confers inducible ectopic cell division. GPA1 overexpression in synchronized BY-2 cells causes premature advance of the nuclear cycle and the premature appearance of a division wall. Results from loss of function and ectopic expression and activation of GPA1 indicate that this subunit is a positive modulator of cell division in plants.

363 citations


Journal ArticleDOI
TL;DR: The results support the involvement of a heterotrimeric G-protein in the light regulation of Arabidopsis seedling development by showing enhanced responses in far-red and red light and a dependence on FHY1 indicates that theArabidopsis Gα protein may act only on a discrete branch of the phytochrome A signaling pathway.
Abstract: Plant heterotrimeric G-proteins have been implicated in a number of signaling processes. However, most of these studies are based on biochemical or pharmacological approaches. To examine the role of heterotrimeric G-proteins in plant development, we generated transgenic Arabidopsis expressing the Gα subunit of the heterotrimeric G-protein under the control of a glucocorticoid-inducible promoter. With the conditional overexpression of either the wild type or a constitutively active version of Arabidopsis Gα, transgenic seedlings exhibited a hypersensitive response to light. This enhanced light sensitivity was more exaggerated in a relatively lower intensity of light and was observed in white light as well as far-red, red, and blue light conditions. The enhanced responses in far-red and red light required functional phytochrome A and phytochrome B, respectively. Furthermore, the response to far-red light depended on functional FHY1 but not on FIN219 and FHY3. This dependence on FHY1 indicates that the Arabidopsis Gα protein may act only on a discrete branch of the phytochrome A signaling pathway. Thus, our results support the involvement of a heterotrimeric G-protein in the light regulation of Arabidopsis seedling development.

99 citations


Journal ArticleDOI
TL;DR: Test data indicate that receptor-mediated inhibition of GIRK channels involves PLC activation by Gα subunits of the Gαqfamily and suggest that inhibition may be communicated at a distance to GirK channels via unbinding and diffusion of phosphatidylinositol bisphosphate away from the channel.

92 citations


Journal ArticleDOI
TL;DR: It is concluded that βγ can activate βs and that this effect probably involves both a tilt of βγ relative to αs and interaction of β with the lip of the nucleotide binding pocket.
Abstract: How receptors catalyze exchange of GTP for GDP bound to the Galpha subunit of trimeric G proteins is not known. One proposal is that the receptor uses the G protein's betagamma heterodimer as a lever, tilting it to pull open the guanine nucleotide binding pocket of Galpha. To test this possibility, we designed a mutant Galpha that would bind to betagamma in the tilted conformation. To do so, we excised a helical turn (four residues) from the N-terminal region of alpha(s), the alpha subunit of G(S), the stimulatory regulator of adenylyl cyclase. In the presence, but not in the absence, of transiently expressed beta(1) and gamma(2), this mutant (alpha(s)Delta), markedly stimulated cAMP accumulation. This effect depended on the ability of the coexpressed beta protein to interact normally with the lip of the nucleotide binding pocket of alpha(s)Delta. We substituted alanine for an aspartate in beta(1) that binds to a lysine (K206) in the lip of the alpha subunit's nucleotide binding pocket. Coexpressed with alpha(s)Delta and gamma(2), this mutant, beta(1)-D228A, elevated cAMP much less than did beta(1)-wild type; it did bind to alpha(s)Delta normally, however, as indicated by its unimpaired ability to target alpha(s)Delta to the plasma membrane. We conclude that betagamma can activate alpha(s) and that this effect probably involves both a tilt of betagamma relative to alpha(s) and interaction of beta with the lip of the nucleotide binding pocket. We speculate that receptors use a similar mechanism to activate trimeric G proteins.

78 citations


Journal ArticleDOI
TL;DR: Immunoprecipitation experiments demonstrated that G αq interacts directly with the C terminus of the α1Bsubunit, consistent with a model in which local activation of PKC by channel-associated Gαq blocks modulation of the channel by Gβγ released by Gq-coupled receptors.
Abstract: Inhibition of calcium channels by G-protein-coupled receptors depends on the nature of the Galpha subunit, although the Gbetagamma complex is thought to be responsible for channel inhibition Ca currents in hypothalamic neurons and N-type calcium channels expressed in HEK-293 cells showed robust inhibition by G(i)/G(o)-coupled galanin receptors (GalR1), but not by Gq-coupled galanin receptors (GalR2) However, deletions in the C terminus of alpha(1B-1) produced Ca channels that were inhibited after activation of both GalR1 and GalR2 Inhibition of protein kinase C (PKC) also revealed Ca current modulation by GalR2 Imaging studies using green fluorescent protein fusions of the C terminus of alpha(1B) demonstrated that activation of the GalR2 receptor caused translocation of the C terminus of alpha(1B-1) to the membrane and co-localization with Galphaq and PKC Similar translocation was not seen with a C-terminal truncated splice variant, alpha(1B-2) Immunoprecipitation experiments demonstrated that Galphaq interacts directly with the C terminus of the alpha(1B) subunit These results are consistent with a model in which local activation of PKC by channel-associated Galphaq blocks modulation of the channel by Gbetagamma released by Gq-coupled receptors

48 citations


Journal ArticleDOI
TL;DR: The results demonstrate that specificity of receptor-G protein signaling can be disrupted by overexpression of receptors, and the alpha subunit of heterotrimeric G proteins does not confer specificity to G beta gamma-mediated signaling.

45 citations


Journal ArticleDOI
TL;DR: Gαq/11 coupled to mammalian PLC β3-like enzyme mediates ginsenoside effect on Ca2+-activated Cl− current in theXenopus oocyte, and antibodies against PLCβ3, but not -β1 and -β2, markedly attenuated the ginsene effect examined.

38 citations


Journal ArticleDOI
TL;DR: Biochemical studies suggest that G proteins mediate a variety of signaling processes in plants, yet Arabidopsis has only one gene, GPA1, for a canonical G protein alpha subunit.

29 citations


Journal ArticleDOI
TL;DR: A combination of G(alpha) affinity chromatography, GTP binding/hydrolysis studies, and genetic analysis allowed us to assign a distinct mechanism of action to each of these mutant proteins.

11 citations


Journal ArticleDOI
TL;DR: Data indicate that Gi(3) activation is required for potentiation of beta(2)-AR stimulation of AC by alpha(2A/D) andalpha(2B)-AR in DDT1-MF2 cells, and partial and full agonists selectively activate G proteins that lead to drug specific effects on effectors.
Abstract: alpha2-Adrenergic receptor (alpha(2)-AR) activation in the pregnant rat myometrium at midterm potentiates beta(2)-AR stimulation of adenylyl cyclase (AC) via Gbetagamma regulation of the type II isoform of adenylyl cyclase. However, at term, alpha(2)-AR activation inhibits beta(2)-AR stimulation of AC. This phenomenon is associated with changes in alpha(2)-AR subtype expression (midterm alpha(2A/D)-AR >> alpha(2B)-AR; term alpha(2B) >or =alpha(2A/D)-AR), without any change in ACII mRNA, suggesting that alpha(2A/D)- and alpha(2B)-AR differentially regulate beta(2)-cAMP production. To address this issue, we have stably expressed the same density of alpha(2A/D)- or alpha(2B)-AR with AC II in DDT1-MF2 cells. Clonidine (partial agonist) increased beta(2)-AR-stimulated cAMP production in alpha(2A/D)-AR-ACII transfectants but inhibited it in alpha(2B)-AR-ACII transfectants. In contrast, epinephrine (full agonist) enhanced beta(2)-stimulated ACII in both alpha(2A)- and alpha(2B)-ACII clonal cell lines. 4-Azidoanilido-[alpha-(32)P]GTP-labeling of activated G proteins indicated that, in alpha(2B)-AR transfectants, clonidine activated only Gi(2), whereas epinephrine, the full agonist, effectively coupled to Gi(2) and Gi(3). Thus, partial and full agonists selectively activate G proteins that lead to drug specific effects on effectors. Moreover, these data indicate that Gi(3) activation is required for potentiation of beta(2)-AR stimulation of AC by alpha(2A/D) and alpha(2B)-AR in DDT1-MF2 cells. This may reflect an issue of the amount of Gbetagamma released upon receptor activation and/or betagamma composition of Gi(3) versus Gi(2).

10 citations


Journal ArticleDOI
TL;DR: The role of GTP binding regulatory 'G' proteins is investigated using cholera and pertussis toxins and an intracellular second messenger cAMP analogue, 8-bromo-cAMP to suggest the involvement of classical heterotrimeric G proteins in the regulation of GPI-anchor biosynthesis through dolichol-phosphate-mannose synthesis via the activation of adenylyl cyclase and protein phosphorylation.