Specificity of Gβ and γ subunits to SNARE complex both at rest and after α 2a adrenergic receptor stimulation

G proteins are major transducers of signals from G-protein coupled receptors (GPCRs). They are made up of α, β, and γ subunits, with 16 Gα, 5 Gβ and 12 Gγ subunits. Though much is known about the specificity of Gα subunits, the specificity of Gβγs by a given GPCR and those that activate each effector is not clear. In a previous paper, we were able to identify Gβ and Gγ interacting specifically neuronal α-adrenergic receptors (αARs). However, it still remains unclear how G protein specificity plays out in αAR-mediated effector interactions. This receptor is the major autoreceptor that acts as a brake to synaptic transmission in adrenergic neurons and the sympathetic nervous system, and as heteroreceptors on other neurons throughout the brain. Here, we examined the specificity of Gβγ to the soluble NSF attachment proteins (SNARE) complex upon presynaptic αAR activation in both adrenergic (auto-αARs) and non-adrenergic (heteroreceptor) neurons for the first time. To understand how this interaction underlies inhibition of synaptic transmission in diverse physiological functions such as spontaneous locomotor activity, anesthetic sparing, and working memory enhancement, we applied a quantitative MRM proteomic analysis of Gβ and Gγ subunits co-immunoprecipitation from transgenic FLAG-αARs and wildtype mice. We evaluated Gβ and Gγ subunit binding to the SNARE complex with and without activation of auto-αAR and hetero-αAR using epinephrine. Without epinephrine stimulation, Gβ and Gγ interact with SNARE. When auto-αARs are activated, Gβ, Gβ, and Gγ interact with SNARE. Further understanding of Gβγ specificity to various effectors offers new insights into the multiplicity of genes for Gβ and Gγ, and the mechanisms underlying GPCR signaling through Gβγ subunits to this interaction as a potential therapeutic target.