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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
J Biol Chem. 2017 292 (29): 12165-12177

PMID: 28515322 · PMCID: PMC5519367 · DOI:10.1074/jbc.M116.773523

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. Infusion 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.

MeSH Terms (24)

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

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