Binding of glutamate receptor δ2 to its scaffold protein, Delphilin, is regulated by PKA

The glutamate receptor δ2 (GluRδ2) is selectively expressed in cerebellar Purkinje cells and plays an important role in motor learning, motor coordination, and long-term depression. Delphilin is identified as a GluRδ2-interacting protein, selectively expressed in Purkinje cell-parallel fiber synapses, and specifically interacts with the GluRδ2 C-terminus via its PDZ domain. Here, surface plasmon resonance analyses showed that Delphilin PDZ bound to GluRδ2 C-terminal peptide (DPDRGTSI), but not to its phosphopeptides (DPDRGphosphoTSI and DPDRGTphosphoSI). We showed the incorporation of phosphate into threonine at −2 (−2T) and serine at −1 (−1S) of GluRδ2 C-terminus by cAMP-dependent protein kinase (PKA) in vitro. In the experiments using heterologous expression system, Delphilin coimmunoprecipitated with GluRδ2 was dramatically decreased under the condition with forskolin and isobutylmethylxanthine, which led to cAMP-dependent phosphorylation by PKA. Thus, phosphorylation of −2T and/or −1S of GluRδ2 C-terminus by PKA may regulate the binding of GluRδ2 to its scaffolding protein, Delphilin.