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Disabling the Gβγ-SNARE interaction disrupts GPCR-mediated presynaptic inhibition, leading to physiological and behavioral phenotypes.
Zurawski Z, Thompson Gray AD, Brady LJ, Page B, Church E, Harris NA, Dohn MR, Yim YY, Hyde K, Mortlock DP, Jones CK, Winder DG, Alford S, Hamm HE
(2019) Sci Signal 12:
MeSH Terms: Animals, Calcium, Exocytosis, GTP-Binding Protein alpha Subunits, Gi-Go, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Mice, Inbred C57BL, Mice, Inbred DBA, Mice, Knockout, Neural Inhibition, Phenotype, Protein Binding, Receptors, G-Protein-Coupled, Synaptic Transmission, Synaptosomal-Associated Protein 25
Show Abstract · Added February 22, 2019
G protein-coupled receptors (GPCRs) that couple to G proteins modulate neurotransmission presynaptically by inhibiting exocytosis. Release of Gβγ subunits from activated G proteins decreases the activity of voltage-gated Ca channels (VGCCs), decreasing excitability. A less understood Gβγ-mediated mechanism downstream of Ca entry is the binding of Gβγ to SNARE complexes, which facilitate the fusion of vesicles with the cell plasma membrane in exocytosis. Here, we generated mice expressing a form of the SNARE protein SNAP25 with premature truncation of the C terminus and that were therefore partially deficient in this interaction. SNAP25Δ3 homozygote mice exhibited normal presynaptic inhibition by GABA receptors, which inhibit VGCCs, but defective presynaptic inhibition by receptors that work directly on the SNARE complex, such as 5-hydroxytryptamine (serotonin) 5-HT receptors and adrenergic α receptors. Simultaneously stimulating receptors that act through both mechanisms showed synergistic inhibitory effects. SNAP25Δ3 homozygote mice had various behavioral phenotypes, including increased stress-induced hyperthermia, defective spatial learning, impaired gait, and supraspinal nociception. These data suggest that the inhibition of exocytosis by G-coupled GPCRs through the Gβγ-SNARE interaction is a crucial component of numerous physiological and behavioral processes.
Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
1 Communities
3 Members
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15 MeSH Terms
Quantitative Multiple-Reaction Monitoring Proteomic Analysis of Gβ and Gγ Subunits in C57Bl6/J Brain Synaptosomes.
Yim YY, McDonald WH, Hyde K, Cruz-Rodríguez O, Tesmer JJG, Hamm HE
(2017) Biochemistry 56: 5405-5416
MeSH Terms: Amino Acid Sequence, Animals, Brain, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Mice, Mice, Inbred C57BL, Protein Multimerization, Protein Structure, Quaternary, Protein Transport, Proteomics, Synaptosomes
Show Abstract · Added March 24, 2020
Gβγ dimers are one of the essential signaling units of activated G protein-coupled receptors (GPCRs). There are five Gβ and 12 Gγ subunits in humans; numerous studies have demonstrated that different Gβ and Gγ subunits selectively interact to form unique Gβγ dimers, which in turn may target specific receptors and effectors. Perturbation of Gβγ signaling can lead to impaired physiological responses. Moreover, previous targeted multiple-reaction monitoring (MRM) studies of Gβ and Gγ subunits have shown distinct regional and subcellular localization patterns in four brain regions. Nevertheless, no studies have quantified or compared their individual protein levels. In this study, we have developed a quantitative MRM method not only to quantify but also to compare the protein abundance of neuronal Gβ and Gγ subunits. In whole and fractionated crude synaptosomes, we were able to identify the most abundant neuronal Gβ and Gγ subunits and their subcellular localizations. For example, Gβ was mostly localized at the membrane while Gβ was evenly distributed throughout synaptosomal fractions. The protein expression levels and subcellular localizations of Gβ and Gγ subunits may affect the Gβγ dimerization and Gβγ-effector interactions. This study offers not only a new tool for quantifying and comparing Gβ and Gγ subunits but also new insights into the in vivo distribution of Gβ and Gγ subunits, and Gβγ dimer assembly in normal brain function.
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MeSH Terms
Gβγ directly modulates vesicle fusion by competing with synaptotagmin for binding to neuronal SNARE proteins embedded in membranes.
Zurawski Z, Page B, Chicka MC, Brindley RL, Wells CA, Preininger AM, Hyde K, Gilbert JA, Cruz-Rodriguez O, Currie KPM, Chapman ER, Alford S, Hamm HE
(2017) J Biol Chem 292: 12165-12177
MeSH Terms: Animals, Binding, Competitive, Calcium Signaling, Cattle, Cell Line, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Humans, Lipid Bilayers, Liposomes, Membrane Fusion, Models, Molecular, Mutation, Nerve Tissue Proteins, Peptide Fragments, Protein Conformation, Protein Interaction Domains and Motifs, Protein Multimerization, Rats, Recombinant Fusion Proteins, Recombinant Proteins, Synaptosomal-Associated Protein 25, Synaptotagmin I, Syntaxin 1
Show Abstract · Added July 12, 2017
G-coupled G protein-coupled receptors can inhibit neurotransmitter release at synapses via multiple mechanisms. In addition to Gβγ-mediated modulation of voltage-gated calcium channels (VGCC), inhibition can also be mediated through the direct interaction of Gβγ subunits with the soluble -ethylmaleimide attachment protein receptor (SNARE) complex of the vesicle fusion apparatus. Binding studies with soluble SNARE complexes have shown that Gβγ binds to both ternary SNARE complexes, t-SNARE heterodimers, and monomeric SNAREs, competing with synaptotagmin 1(syt1) for binding sites on t-SNARE. However, in secretory cells, Gβγ, SNAREs, and synaptotagmin interact in the lipid environment of a vesicle at the plasma membrane. To approximate this environment, we show that fluorescently labeled Gβγ interacts specifically with lipid-embedded t-SNAREs consisting of full-length syntaxin 1 and SNAP-25B at the membrane, as measured by fluorescence polarization. Fluorescently labeled syt1 undergoes competition with Gβγ for SNARE-binding sites in lipid environments. Mutant Gβγ subunits that were previously shown to be more efficacious at inhibiting Ca-triggered exocytotic release than wild-type Gβγ were also shown to bind SNAREs at a higher affinity than wild type in a lipid environment. These mutant Gβγ subunits were unable to inhibit VGCC currents. Specific peptides corresponding to regions on Gβ and Gγ shown to be important for the interaction disrupt the interaction in a concentration-dependent manner. In fusion assays using full-length t- and v-SNAREs embedded in liposomes, Gβγ inhibited Ca/synaptotagmin-dependent fusion. Together, these studies demonstrate the importance of these regions for the Gβγ-SNARE interaction and show that the target of Gβγ, downstream of VGCC, is the membrane-embedded SNARE complex.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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2 Members
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24 MeSH Terms
A Presynaptic Group III mGluR Recruits Gβγ/SNARE Interactions to Inhibit Synaptic Transmission by Cone Photoreceptors in the Vertebrate Retina.
Van Hook MJ, Babai N, Zurawski Z, Yim YY, Hamm HE, Thoreson WB
(2017) J Neurosci 37: 4618-4634
MeSH Terms: Ambystoma, Animals, Excitatory Postsynaptic Potentials, Female, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Male, Receptors, Metabotropic Glutamate, Retinal Cone Photoreceptor Cells, Retinal Horizontal Cells, SNARE Proteins, Synapses, Synaptic Transmission
Show Abstract · Added March 24, 2020
G-protein βγ subunits (Gβγ) interact with presynaptic proteins and regulate neurotransmitter release downstream of Ca influx. To accomplish their roles in sensory signaling, photoreceptor synapses use specialized presynaptic proteins that support neurotransmission at active zone structures known as ribbons. While several G-protein coupled receptors (GPCRs) influence synaptic transmission at ribbon synapses of cones and other retinal neurons, it is unknown whether Gβγ contributes to these effects. We tested whether activation of one particular GPCR, a metabotropic glutamate receptor (mGluR), can reduce cone synaptic transmission via Gβγ in tiger salamander retinas. In recordings from horizontal cells, we found that an mGluR agonist (L-AP4) reduced cone-driven light responses and mEPSC frequency. In paired recordings of cones and horizontal cells, L-AP4 slightly reduced cone I (∼10%) and caused a larger reduction in cone-driven EPSCs (∼30%). Proximity ligation assay revealed direct interactions between SNAP-25 and Gβγ subunits in retinal synaptic layers. Pretreatment with the SNAP-25 cleaving protease BoNT/A inhibited L-AP4 effects on synaptic transmission, as did introduction of a peptide derived from the SNAP-25 C terminus. Introducing Gβγ subunits directly into cones reduced EPSC amplitude. This effect was inhibited by BoNT/A, supporting a role for Gβγ/SNAP-25 interactions. However, the mGluR-dependent reduction in I was not mimicked by Gβγ, indicating that this effect was independent of Gβγ. The finding that synaptic transmission at cone ribbon synapses is regulated by Gβγ/SNAP-25 interactions indicates that these mechanisms are shared by conventional and ribbon-type synapses. Gβγ liberated from other photoreceptor GPCRs is also likely to regulate synaptic transmission. Dynamic regulation of synaptic transmission by presynaptic G-protein coupled receptors shapes information flow through neural circuits. At the first synapse in the visual system, presynaptic metabotropic glutamate receptors (mGluRs) regulate cone photoreceptor synaptic transmission, although the mechanisms and functional impact of this are unclear. We show that mGluRs regulate light response encoding across the cone synapse, accomplished in part by triggering G-protein βγ subunits (Gβγ) interactions with SNAP-25, a core component of the synaptic vesicle fusion machinery. In addition to revealing a role in visual processing, this provides the first demonstration that Gβγ/SNAP-25 interactions regulate synaptic function at a ribbon-type synapse, contributing to an emerging picture of the ubiquity of Gβγ/SNARE interactions in regulating synaptic transmission throughout the nervous system.
Copyright © 2017 the authors 0270-6474/17/374619-17$15.00/0.
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MeSH Terms
Gβγ Binds to the Extreme C Terminus of SNAP25 to Mediate the Action of Gi/o-Coupled G Protein-Coupled Receptors.
Zurawski Z, Rodriguez S, Hyde K, Alford S, Hamm HE
(2016) Mol Pharmacol 89: 75-83
MeSH Terms: Animals, Cattle, GTP-Binding Protein alpha Subunits, Gi-Go, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Mice, Petromyzon, Protein Binding, Protein Structure, Secondary, Synaptosomal-Associated Protein 25
Show Abstract · Added March 24, 2020
Gi/o-coupled G protein-coupled receptors can exert an inhibitory effect on vesicle release through several G protein-driven mechanisms, more than one of which may be concurrently present in individual presynaptic terminals. The synaptosomal-associated protein of 25 kDa (SNAP25) is a key downstream effector of Gβγ subunits. It has previously been shown that proteolytic cleavage of SNAP25 by botulinum toxin A reduces the ability of Gβγ to compete with the calcium sensor synaptotagmin 1 (Syt1) for binding to SNAP25 in a calcium-dependent manner. These truncated SNAP25 proteins sustain a low level of exocytosis but are unable to support serotonin-mediated inhibition of exocytosis in lamprey spinal neurons. Here, we generate a SNAP25 extreme C-terminal mutant that is deficient in its ability to bind Gβγ while retaining normal calcium-dependent Syt1 binding to soluble N-ethylmaleimide attachment protein receptor (SNARE) and vesicle release. The SNAP25Δ3 mutant, in which residue G204 is replaced by a stop codon, features a partial reduction in Gβ1γ2 binding in vitro as well as a partial reduction in the ability of the lamprey 5-hydroxytryptamine1b-type serotonin receptor to reduce excitatory postsynaptic current amplitudes, an effect previously shown to be mediated through the interaction of Gβγ with SNAP25. Syt1 calcium-dependent binding to SNAP25Δ3 was reduced by a small extent compared with the wild type. We conclude that the extreme C terminus of SNAP25 is a critical region for the Gβγ-SNARE interaction.
Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.
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1 Members
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MeSH Terms
Differential stimulation of insulin secretion by GLP-1 and Kisspeptin-10.
Schwetz TA, Reissaus CA, Piston DW
(2014) PLoS One 9: e113020
MeSH Terms: Animals, Blood Glucose, Calcium, Calcium Signaling, GTP-Binding Protein alpha Subunits, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Glucagon-Like Peptide 1, Humans, Insulin, Insulin-Secreting Cells, Islets of Langerhans, Kisspeptins, Male, Mice, Oxidation-Reduction, Signal Transduction
Show Abstract · Added January 20, 2015
β-cells in the pancreatic islet respond to elevated plasma glucose by secreting insulin to maintain glucose homeostasis. In addition to glucose stimulation, insulin secretion is modulated by numerous G-protein coupled receptors (GPCRs). The GPCR ligands Kisspeptin-10 (KP) and glucagon-like peptide-1 (GLP-1) potentiate insulin secretion through Gq and Gs-coupled receptors, respectively. Despite many studies, the signaling mechanisms by which KP and GLP-1 potentiate insulin release are not thoroughly understood. We investigated the downstream signaling pathways of these ligands and their affects on cellular redox potential, intracellular calcium activity ([Ca(2+)]i), and insulin secretion from β-cells within intact murine islets. In contrast to previous studies performed on single β-cells, neither KP nor GLP-1 affect [Ca(2+)]i upon stimulation with glucose. KP significantly increases the cellular redox potential, while no effect is observed with GLP-1, suggesting that KP and GLP-1 potentiate insulin secretion through different mechanisms. Co-treatment with KP and the Gβγ-subunit inhibitor gallein inhibits insulin secretion similar to that observed with gallein alone, while co-treatment with gallein and GLP-1 does not differ from GLP-1 alone. In contrast, co-treatment with the Gβγ activator mSIRK and either KP or GLP-1 stimulates insulin release similar to mSIRK alone. Neither gallein nor mSIRK alter [Ca(2+)]i activity in the presence of KP or GLP-1. These data suggest that KP likely alters insulin secretion through a Gβγ-dependent process that stimulates glucose metabolism without altering Ca(2+) activity, while GLP-1 does so, at least partly, through a Gα-dependent pathway that is independent of both metabolism and Ca(2+).
0 Communities
1 Members
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17 MeSH Terms
Differential localization of G protein βγ subunits.
Betke KM, Rose KL, Friedman DB, Baucum AJ, Hyde K, Schey KL, Hamm HE
(2014) Biochemistry 53: 2329-43
MeSH Terms: Amino Acid Sequence, Animals, Chromatography, Liquid, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Male, Mice, Mice, Inbred C57BL, Molecular Sequence Data, Protein Isoforms, Signal Transduction, Subcellular Fractions, Synaptosomes, Tandem Mass Spectrometry
Show Abstract · Added May 27, 2014
G protein βγ subunits play essential roles in regulating cellular signaling cascades, yet little is known about their distribution in tissues or their subcellular localization. While previous studies have suggested specific isoforms may exhibit a wide range of distributions throughout the central nervous system, a thorough investigation of the expression patterns of both Gβ and Gγ isoforms within subcellular fractions has not been conducted. To address this, we applied a targeted proteomics approach known as multiple-reaction monitoring to analyze localization patterns of Gβ and Gγ isoforms in pre- and postsynaptic fractions isolated from cortex, cerebellum, hippocampus, and striatum. Particular Gβ and Gγ subunits were found to exhibit distinct regional and subcellular localization patterns throughout the brain. Significant differences in subcellular localization between pre- and postsynaptic fractions were observed within the striatum for most Gβ and Gγ isoforms, while others exhibited completely unique expression patterns in all four brain regions examined. Such differences are a prerequisite for understanding roles of individual subunits in regulating specific signaling pathways throughout the central nervous system.
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2 Members
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14 MeSH Terms
Gβγ inhibits exocytosis via interaction with critical residues on soluble N-ethylmaleimide-sensitive factor attachment protein-25.
Wells CA, Zurawski Z, Betke KM, Yim YY, Hyde K, Rodriguez S, Alford S, Hamm HE
(2012) Mol Pharmacol 82: 1136-49
MeSH Terms: Alanine, Animals, Binding Sites, Botulinum Toxins, Calcium, Cell Line, Exocytosis, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Lampreys, Mutation, Neurons, Peptides, Protein Binding, Protein Interaction Domains and Motifs, Recombinant Fusion Proteins, SNARE Proteins, Sf9 Cells, Spodoptera, Synaptosomal-Associated Protein 25, Synaptotagmin I, Syntaxin 1
Show Abstract · Added December 10, 2013
Spatial and temporal regulation of neurotransmitter release is a complex process accomplished by the exocytotic machinery working in tandem with numerous regulatory proteins. G-protein βγ dimers regulate the core process of exocytosis by interacting with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins soluble N-ethylmaleimide-sensitive factor attachment protein-25 (SNAP-25), syntaxin 1A, and synaptobrevin. Gβγ binding to ternary SNAREs overlaps with calcium-dependent binding of synaptotagmin, inhibiting synaptotagmin-1 binding and fusion of the synaptic vesicle. To further explore the binding sites of Gβγ on SNAP-25, peptides based on the sequence of SNAP-25 were screened for Gβγ binding. Peptides that bound Gβγ were subjected to alanine scanning mutagenesis to determine their relevance to the Gβγ-SNAP-25 interaction. Peptides from this screen were tested in protein-protein interaction assays for their ability to modulate the interaction of Gβγ with SNAP-25. A peptide from the C terminus, residues 193 to 206, significantly inhibited the interaction. In addition, Ala mutants of SNAP-25 residues from the C terminus of SNAP-25, as well as from the amino-terminal region decreased binding to Gβ₁γ₁. When SNAP-25 with eight residues mutated to alanine was assembled with syntaxin 1A, there was significantly reduced affinity of this mutated t-SNARE for Gβγ, but it still interacted with synaptotagmin-1 in a Ca²⁺ -dependent manner and reconstituted evoked exocytosis in botulinum neurotoxin E-treated neurons. However, the mutant SNAP-25 could no longer support 5-hydroxytryptamine-mediated inhibition of exocytosis.
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1 Members
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22 MeSH Terms
GPCR mediated regulation of synaptic transmission.
Betke KM, Wells CA, Hamm HE
(2012) Prog Neurobiol 96: 304-21
MeSH Terms: Animals, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Humans, Receptors, G-Protein-Coupled, Synaptic Membranes, Synaptic Transmission
Show Abstract · Added December 10, 2013
Synaptic transmission is a finely regulated mechanism of neuronal communication. The release of neurotransmitter at the synapse is not only the reflection of membrane depolarization events, but rather, is the summation of interactions between ion channels, G protein coupled receptors, second messengers, and the exocytotic machinery itself which exposes the components within a synaptic vesicle to the synaptic cleft. The focus of this review is to explore the role of G protein signaling as it relates to neurotransmission, as well as to discuss the recently determined inhibitory mechanism of Gβγ dimers acting directly on the exocytotic machinery proteins to inhibit neurotransmitter release.
Copyright © 2012 Elsevier Ltd. All rights reserved.
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1 Members
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7 MeSH Terms
Regulator of G protein signaling 6 (RGS6) protein ensures coordination of motor movement by modulating GABAB receptor signaling.
Maity B, Stewart A, Yang J, Loo L, Sheff D, Shepherd AJ, Mohapatra DP, Fisher RA
(2012) J Biol Chem 287: 4972-81
MeSH Terms: Animals, Baclofen, Cerebellar Ataxia, Cerebellum, G Protein-Coupled Inwardly-Rectifying Potassium Channels, GABA-B Receptor Agonists, GABAergic Neurons, GTP-Binding Protein beta Subunits, Humans, Locomotion, Mice, Mice, Knockout, Motor Activity, Multiprotein Complexes, Nerve Tissue Proteins, RGS Proteins, Receptors, GABA-B, Signal Transduction
Show Abstract · Added August 7, 2014
γ-Aminobutyric acid (GABA) release from inhibitory interneurons located within the cerebellar cortex limits the extent of neuronal excitation in part through activation of metabotropic GABA(B) receptors. Stimulation of these receptors triggers a number of downstream signaling events, including activation of GIRK channels by the Gβγ dimer resulting in membrane hyperpolarization and inhibition of neurotransmitter release from presynaptic sites. Here, we identify RGS6, a member of the R7 subfamily of RGS proteins, as a key regulator of GABA(B)R signaling in cerebellum. RGS6 is enriched in the granule cell layer of the cerebellum along with neuronal GIRK channel subunits 1 and 2 where RGS6 forms a complex with known binding partners Gβ(5) and R7BP. Mice lacking RGS6 exhibit abnormal gait and ataxia characterized by impaired rotarod performance improved by treatment with a GABA(B)R antagonist. RGS6(-/-) mice administered baclofen also showed exaggerated motor coordination deficits compared with their wild-type counterparts. Isolated cerebellar neurons natively expressed RGS6, GABA(B)R, and GIRK channel subunits, and cerebellar granule neurons from RGS6(-/-) mice showed a significant delay in the deactivation kinetics of baclofen-induced GIRK channel currents. These results establish RGS6 as a key component of GABA(B)R signaling and represent the first demonstration of an essential role for modulatory actions of RGS proteins in adult cerebellum. Dysregulation of RGS6 expression in human patients could potentially contribute to loss of motor coordination and, thus, pharmacological manipulation of RGS6 levels might represent a viable means to treat patients with ataxias of cerebellar origin.
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18 MeSH Terms