PSD-95/SAP90 is a member of membrane-associated guanylate kinases localized at postsynaptic density (PSD) in neuronal cells. Membrane-associated guanylate kinases are a family of signaling molecules expressed at various submembrane domains which have the PDZ (DHR) domains, the SH3 domain, and the guanylate kinase domain. PSD-95/SAP90 interacts with Nmethyl-D-aspartate receptors 2A/B, Shaker-type potassium channels, and brain nitric oxide synthase through the PDZ (DHR) domains and clusters these

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... molecules at synaptic junctions. However, neither the function of the SH3 domain or the guanylate kinase domain of PSD-95/ SAP90, nor the protein interacting with these domains has been identified. We have isolated here a novel protein family consisting of at least four members which specifically interact with PSD-95/SAP90 and its related proteins through the guanylate kinase domain, and named these proteins SAPAPs (SAP90/PSD-95-Associated Proteins). SAPAPs are specifically expressed in neuronal cells and enriched in the PSD fraction. SAPAPs induce the enrichment of PSD-95/SAP90 to the plasma membrane in transfected cells. Thus, SAPAPs may have a potential activity to maintain the structure of PSD by concentrating its components to the membrane area. * The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. The nucleotide sequence(s) reported in this paper has been submitted to the GenBank TM /EBI Data Bank with accession number(s) U67137-67140 for SAPAPs and U53367 for PSRP1. . 1 The abbreviations used are: PSD, postsynaptic density; NMDA, N-methyl-D-aspartate; MAGUK, membrane-associated guanylate kinase; SAPAP, SAP90/PSD-95-associated protein; GST, glutathione Stransferase; MBP, maltose-binding protein; PAGE, polyacrylamide gel electrophoresis; PSRP1, PSD-95/SAP90-related protein 1; kb, kilobase pair(s).