Guanylate kinase-associated protein (GKAP; also known as synapse-associated 42 protein 90-postsynaptic density-95-associated protein (SAPAP) and Discs-large-associated 43 protein (DAP) family proteins) a synaptic protein is one of the major constituent of the postsynaptic density (PSD). GKAP binds directly to the GK (guanylate kinase-like) domain of the four known members of the PSD-95 (postsynaptic density protein 95) family (Kim et al. 1997, Naisbitt et al. 1997, Takeuchi et al. 1997). GKAP is therefore one of the major scaffold proteins organizing glutamate receptors in the PSD.