Interaction of α1‐syntrophin with multiple isoforms of heterotrimeric G protein α subunits

Syntrophins are components of the dystrophin–glycoprotein complex of the plasma membrane in muscular and neuronal cells, and recruit signaling proteins such as neuronal nitric oxide synthase via their multiple protein–protein interaction motifs. In this study, we found that α1‐syntrophin binds to various subtypes of guanine nucleotide‐binding protein α subunits (Gα). A pull‐down analysis using full‐length recombinant α1‐syntrophin and MS analysis showed that α1‐syntrophin was coprecipitated with several isoforms of Gα proteins in addition to known binding partners such as dystrobrevin and neuronal nitric oxide synthase. Further analysis using recombinant Gα isoforms showed that α1‐syntrophin associates with at least Gαi, Gαo, Gαs and Gαq subtypes. The region of α1‐syntrophin required for its interaction with Gαs was determined as the N‐terminal half of the first pleckstrin homology domain. In addition, the syntrophin unique domain of α1‐syntrophin was suggested to contribute to this interaction. In COS‐7 cells, downregulation of α1‐syntrophin by RNAi resulted in enhanced cAMP production and cAMP response element‐binding protein phosphorylation induced by isoproterenol treatment. These results suggest that α1‐syntrophin provides a scaffold for the Gα family of heterotrimeric G proteins in the brain to regulate the efficiency of signal transduction evoked by G‐protein‐coupled receptors.