Part of the postsynaptic scaffold in neuronal cells. Interacts with guanylate kinase-like domain of DLG1, DLG2, DLG3, DLG4 and AIP1. Interacts with the PDZ domain of SHANK1, SHANK2 and SHANK3. Found in a complex with DLG4 and SHANK1, SHANK2 or SHANK3. Found in a complex with DLG4 and BEGAIN. Interacts with DYL2 and LRFN1 (By similarity). Interacts with MPP2 (via the SH3-Guanylate kinase-like sub-module) (By similarity). Expressed in brain. Belongs to the SAPAP family.