PSD-95 interacts with GKAP through its GK domain (Kim et al. 1997). In turn, the C-terminus of GKAP binds to the Shank family of PDZ-containing scaffold proteins. The Shank family of proteins is highly enriched in the postsynaptic density (PSD) of excitatory synapses in brain. There are three known SHANK proteins: SHANK1, SHANK2, and SHANK3. SHANK contains multiple domains for protein-protein interactions, including ankyrin repeats, SH3 domain, PDZ domain, SAM domain, and an extensive proline-rich region (Sheng & Kim 2000). Shank may function as a scaffold protein in the PSD, potentially cross-linking NMDA receptor or Neuroligin:PSD-95 complexes and coupling them to regulators of the actin cytoskeleton (Naisbitt et al.1999).