GTPase acceleration as the rate-limiting step in
            <i>Arabidopsis</i>
            G protein-coupled sugar signaling

Johnston, Christopher A.; Taylor, James L.; Gao, Yajun; Kimple, Adam J.; Grigston, Jeffrey C.; Chen, Jay; Siderovski, David P.; Jones, Alan M.; Willard, Francis S.

doi:10.1073/pnas.0704751104

Cited by 198 publications

(278 citation statements)

References 38 publications

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“…We purified this protein and measured its nucleotide exchange rate in a fluorescence assay (GTP-bound Gα proteins have higher intrinsic fluorescence than GDP-bound G proteins) (17). Consistent with a previous study (6), wild-type GPA1 had a spontaneous rate of nucleotide exchange that was fast relative to that of wild-type Gα i1 (Fig. 4B).…”

Section: Gpa1 and Gα I1 Exhibit Different Frequencies Of Two-domain Msupporting

confidence: 92%

“…We chose to study GPA1 because basal nucleotide exchange is >100-fold faster than that of Gα i1 under optimal conditions for each enzyme (6,8). Despite large differences in activation rates, GPA1 and Gα i1 crystal structures (9,10) show remarkable similarity, with an average root-mean-square deviation of only 1.4 Å in core residue Cα atoms (Fig.…”

Section: Gpa1 and Gα I1mentioning

confidence: 99%

“…However, G proteins exhibit a large spectrum of nucleotide exchange and hydrolysis rates. Basal nucleotide exchange in Gα q , for example, is essentially undetectable without a receptor (5), whereas the Gα protein (GPA1) from the plant Arabidopsis thaliana exchanges nucleotides at a pace of at least 4/min (6). Thus, GPA1 serves as a counterexample to slowly exchanging animal proteins and provides an opportunity to compare the molecular basis for receptor-dependent and -independent signaling.…”

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confidence: 99%

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Differences in intradomain and interdomain motion confer distinct activation properties to structurally similar Gα proteins

Jones¹,

Jones²,

Temple

et al. 2012

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

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Proteins with similar crystal structures can have dissimilar rates of substrate binding and catalysis. Here we used molecular dynamics simulations and biochemical analysis to determine the role of intradomain and interdomain motions in conferring distinct activation rates to two Gα proteins, Gα i1 and GPA1. Despite high structural similarity, GPA1 can activate itself without a receptor, whereas Gα i1 cannot. We found that motions in these proteins vary greatly in type and frequency. Whereas motion is greatest in the Ras domain of Gα i1 , it is greatest in helices αA and αB from the helical domain of GPA1. Using protein chimeras, we show that helix αA from GPA1 is sufficient to confer rapid activation to Gα i1 . Gα i1 has less intradomain motion than GPA1 and instead displays interdomain displacement resembling that observed in a receptor-heterotrimer crystal complex. Thus, structurally similar proteins can have distinct atomic motions that confer distinct activation mechanisms.H eterotrimeric G proteins are molecular switches that are activated in response to extracellular stimuli including hormones, light, and neurotransmitters. In animals, the G-protein heterotrimer is activated by cell-surface receptors that trigger the Gα subunit of the heterotrimer to release GDP and bind GTP. GTP binding induces conformational changes in three small switch regions that result in heterotrimer dissociation (1). The free subunits then relay signals by activating or inhibiting downstream effectors. G-protein signaling is terminated after Gα hydrolyzes GTP and the heterotrimer reassociates. Thus, Gα proteins serve as timing devices that determine the duration of signaling.Gα proteins from different organisms and subclasses share nearly identical structural features (2-4). However, G proteins exhibit a large spectrum of nucleotide exchange and hydrolysis rates. Basal nucleotide exchange in Gα q , for example, is essentially undetectable without a receptor (5), whereas the Gα protein (GPA1) from the plant Arabidopsis thaliana exchanges nucleotides at a pace of at least 4/min (6). Thus, GPA1 serves as a counterexample to slowly exchanging animal proteins and provides an opportunity to compare the molecular basis for receptor-dependent and -independent signaling.The Gα subunit is composed of two domains connected by two short linker regions: (i) a domain that resembles the monomeric G protein Ras and (ii) an all α-helical domain unique to heterotrimeric G proteins. The guanine nucleotide binds at the interface of the two domains, but nucleotide-binding residues and switch regions are contained within the Ras domain and linker regions. The recently solved cocrystal structure of a G-protein heterotrimer with an activated receptor shows a large receptorinduced displacement of the Gα helical domain relative to the Ras domain (7). It is unclear whether this interdomain rearrangement is the cause or the consequence of nucleotide release. Nonetheless this work shows that both intradomain and interdomain rearrangements are required for G-p...

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Section: Gpa1 and Gα I1 Exhibit Different Frequencies Of Two-domain Msupporting

confidence: 92%

Section: Gpa1 and Gα I1mentioning

confidence: 99%

mentioning

confidence: 99%

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Differences in intradomain and interdomain motion confer distinct activation properties to structurally similar Gα proteins

Jones¹,

Jones²,

Temple

et al. 2012

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

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“…Heterotrimeric G-proteins are conserved signaling components across diverse eukaryote species (Jones and Assmann, 2004;Johnston et al, 2007;Jones et al, 2011aJones et al, , 2011b. Upon perception of a cognate ligand by its seven-transmembrane receptor on the cell surface, the seven-transmembrane receptor-associated heterotrimeric G-protein complex dissociates to form an activated Ga-subunit and an obligate Gbg dimer, which in turn trigger transient cellular changes by interacting with downstream proteins, typically enzymes, called effectors.…”

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confidence: 99%

Dissecting Arabidopsis Gβ Signal Transduction on the Protein Surface

et al. 2012

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The heterotrimeric G-protein complex provides signal amplification and target specificity. The Arabidopsis (Arabidopsis thaliana) Gb-subunit of this complex (AGB1) interacts with and modulates the activity of target cytoplasmic proteins. This specificity resides in the structure of the interface between AGB1 and its targets. Important surface residues of AGB1, which were deduced from a comparative evolutionary approach, were mutated to dissect AGB1-dependent physiological functions. Analysis of the capacity of these mutants to complement well-established phenotypes of Gb-null mutants revealed AGB1 residues critical for specific AGB1-mediated biological processes, including growth architecture, pathogen resistance, stomata-mediated leaf-air gas exchange, and possibly photosynthesis. These findings provide promising new avenues to direct the finely tuned engineering of crop yield and traits.

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“…Biochemical analysis suggests that AtGPA1 is a unique heterotrimeric G-protein a-subunit that binds constitutively to GTP. It is suggested that high Glc modulates the GTPase-activating protein activity of AtRGS1 to inhibit AtGPA1 (Johnston et al, 2007). This Glc-sensing mechanism is distinct from the HXK1 pathway.…”

Section: Connecting the Sugar Signaling Networkmentioning

confidence: 99%

Discover and Connect Cellular Signaling

Sheen

2010

Plant Physiology

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The unique nature of the plant system as a selfsufficient, robust, and resilient organism requires the dynamic coordination of numerous signal transduction pathways in multiple organs and cell types with complementary functions to capture energy and nutrients, to orchestrate growth and development, to adjust or adapt to fluctuating environment, and to live with symbiotic or curb invasive microbes and animals. Plants "move" through their growth and developmental programs highly integrated with the complex environmental cues. Our understanding of plant signal transduction pathways has been greatly facilitated by the isolation and characterization of a wealth of mutant collections in Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), barley (Hordeum vulgare), pea (Pisum sativum), tomato (Solanum lycopersicum), Medicago truncatula, moss (Physcomitrella patens), Chlamydomonas reinhardtii, and many other plants. A quantum leap in the field was made possible when the molecular cloning of mutated genes and transgenic plant analysis became a reality in several reference plants in the past two decades. Although the mainstream research on signal transduction has focused on single signals and linear pathways, recent findings have revealed many previously unexpected signaling interconnections, manifesting both the complexity and reality (Fig. 1). The increasing availability of annotated plant genome sequences and large-scale genome-wide databases and computational tools have further empowered the dissection of signaling pathways based on traditional characterization in whole plants, organs, or tissues. Moving forward to discovering and connecting the cellular signaling networks, functional characterization of thousands of genes encoding large families of key regulatory components (Fig. 1) in single cell resolution with time kinetics will be the next challenge. Integrative approaches combing creative genetics, sensitive mass spectrometry, genome-wide screens, powerful bioinformatics tools and skills, versatile cell-based assays, and targeted mutagenesis will be critical for future discoveries (Fig. 2). Glc signaling networks and emerging research tools are briefly highlighted to help pave the way for future research in cellular signaling. CONNECTING THE SUGAR SIGNALING NETWORKCharacterization of plant signaling pathways has been remarkably successful based on single signals (e.g. hormones, stresses, and microbial elicitors) and phenotypic or reporter-based observation of insensitive, constitutive, or hypersensitive response mutants, especially in Arabidopsis and rice. General frameworks, often with linear relationship of positive or negative regulators, for many plant signaling pathways have been established based on the initial signals applied in the mutant screens and molecular identification of the mutated genes. However, Arabidopsis mutant screens with an unconventional signal such as Glc (e.g. at high concentrations to trigger developmental arrest of seedlings) have reve...

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GTPase acceleration as the rate-limiting step in Arabidopsis G protein-coupled sugar signaling

Cited by 198 publications

References 38 publications

Differences in intradomain and interdomain motion confer distinct activation properties to structurally similar Gα proteins

Differences in intradomain and interdomain motion confer distinct activation properties to structurally similar Gα proteins

Dissecting Arabidopsis Gβ Signal Transduction on the Protein Surface

Discover and Connect Cellular Signaling

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