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 alpha 1-syntrophin binds to various subtypes of guanine nucleotide-binding protein alpha subunits (G alpha). A pull-down analysis using full-length recombinant alpha 1-syntrophin and MS analysis showed that alpha 1-syntrophin was coprecipitated with several isoforms of G alpha proteins in addition to known binding partners such as dystrobrevin and neuronal nitric oxide synthase. Further analysis using recombinant G alpha isoforms showed that alpha 1-syntrophin associates with at least G alpha i, G alpha o, G alpha s and G alpha q subtypes. The region of alpha 1-syntrophin required for its interaction with G alpha s was determined as the N-terminal half of the first pleckstrin homology domain. In addition, the syntrophin unique domain of alpha 1-syntrophin was suggested to contribute to this interaction. In COS-7 cells, downregulation of alpha 1-syntrophin by RNAi resulted in enhanced cAMP production and cAMP response element-binding protein phosphorylation induced by isoproterenol treatment. These results suggest that alpha 1-syntrophin provides a scaffold for the G alpha family of heterotrimeric G proteins in the brain to regulate the efficiency of signal transduction evoked by G-protein-coupled receptors.