Postsynaptic scaffolding protein at the Purkinje cell synapse, where it may serve to link GRID2 with actin cytoskeleton and various signaling molecules. Interacts with C-terminus of the glutamate receptor GRID2 via PDZ domain. Isoform 2 interacts also with Profilin-2/PFN2 and with the monocarboxylate transporter SLC16A7 via PDZ domain. The interaction of isoform 2 with GRID2 is dependent on GRID2 phosphorylation by PKA. Localized to the postsynaptic junction site of the parallel fiber-Purkinje cell synapse. Highly present in the dendritic spines. Localized at the dendritic spines, but also in dendritic shafts apart fron spines. Isoform 1 is expressed in the cerebellum, but not in the cerebral cortex. Isoform 2 is expressed in the cell body of purkinge cells of the cerebellum and weakly expressed in the cerebrum and the brainstem as well as various nuclei of the thalamus. Isoform 2 is highly expressed in the cerebral cortex than in the cerebellum. Isoform 3 is expressed in the cerebellum and cerebrum. Isoform 3 expression is maintained throughout cerebellar development, while isoform 2 expression gradually decrease following the first postnatal week. PDZ 1 domain is responsible for cytoplasmic clustering of isoform 1. Isoform 2 is palmitoylated. Palmitoylation of isoform 2 is necessary for the enhanced cell surface expression of GRID2, and is also responsible for the accumulation of isoform 2 within dendritic spines. Isoform 1 and isoform 2 are differentially localized, probably modulating GRID2 signaling in neurons. Isoform 1 shows a punctate distribution throughout the cytoplasm when expressed in COS cells, whereas isoform 2 is enriched at the edges of the plasma membranes. When expressed in cultured hippocampal neurons, isoform 1 forms clusters mainly in the dendritic shafts, whereas isoform 2 is preferentially expressed in spines. Not palmitoylated. When Cys-3 is mutated to Ala-3, isoform 2 is not palmitoylated anymore.