Probable adapter protein that bind to and organize the subcellular localization of a variety of membrane proteins containing some PDZ recognition sequence. Involved in the clustering of various receptors, possibly by acting at the receptor internalization level. Plays a role in synaptic plasticity by regulating the trafficking and internalization of AMPA receptors. May be regulated upon PRKCA activation. May regulate ASIC1/ASIC3 channel. Regulates actin polymerization by inhibiting the actin-nucleating activity of the Arp2/3 complex; the function is competitive with nucleation promoting factors and is linked to neuronal morphology regulation and AMPA receptor (AMPAR) endocytosis. Via interaction with the Arp2/3 complex involved in regulation of synaptic plasicity of excitatory synapses and required for spine shrinkage during long-term depression (LTD). Involved in regulation of astrocyte morphology, antagonistic to Arp2/3 complex activator WASL/N-WASP function (By similarity). Monomer and homodimer. Interacts with CXADR. Interacts presynaptically with the glutamate receptors GRIA2, GRIA3, GRIK3, isoform 3 of GRIA4, isoform A of GRM4, GRM7 and GRM8; with NAPA and NAPB; and with BTG2. The interaction with NAPA and NAPB disrupts the interaction with GRIA2, conducting to the internalization of GRIA2. Interacts with PRKCA; with the amine transporters SLC6A2 and SLC6A3; with the channels ASIC1 and ASIC2; with the GTP-binding proteins ARF1 and ARF3; with the ephrin receptor tyrosine kinases EPHA7, EPHB1 and EPHB2; with ERBB2 and through its PDZ domain with the C-terminal tail of PRLHR. Interacts with UNC5A. Interacts (via AH domain) with NCS1/FREQ; in a calcium-dependent manner. Interacts with F-actin and associates with the ARP2/3 complex. Interacts (via PDZ domain) with ARF1 (activated); the interaction blocks Arp2/3 complex inhibition (By similarity). Also membrane-associated, present at excitatory synapses. The AH domain mediates binding to F-actin. The unoccupied PDZ domain is probably involved in allosteric modulation by forming an intramolecular bridge with the AH domain leading to a 'closed' formation. Binding of a PDZ ligand, such as GRIA2, allows enhanced interactions with F-actin and the Arp2/3 complex thus enhanced inhibition of actin polymerization (By similarity). Phosphorylation at Thr-82 appears to inhibit the interaction with AMPA receptors. Palmitoylation on Cys-413 is essential for long-term synaptic depression (LTD).