A Novel Multiple PDZ Domain-containing Molecule Interacting withN-Methyl-d-aspartateReceptors and Neuronal Cell Adhesion Proteins

Abstract

At synaptic junctions, pre-and postsynaptic membranes are connected by cell adhesion and have distinct structures for specialized functions. The presynaptic membranes have a machinery for fast neurotransmitter release, and the postsynaptic membranes have clusters of neurotransmitter receptors. The molecular mechanism of the assembly of synaptic junctions is not yet clear. Pioneering studies identified postsynaptic density (PSD)-95/SAP90 as a prototypic synaptic scaffolding protein to maintain the structure of synaptic junctions. PSD-95/SAP90 belongs to a family of membrane-associated guanylate kinases and binds N-methyl-D-aspartate receptors, potassium channels, and neuroligins through the PDZ domains and GKAP/SAPAP/DAP through the guanylate kinase (GK) domain. We performed here a yeast two-hybrid screening for SAPAP-interacting molecules and identified a novel protein that has an inverse structure of membrane-associated guanylate kinases with an NH 2 -terminal GK-like domain followed by two WW and five PDZ domains. It binds SAPAP through the GK-like domain and NMDA receptors and neuroligins through the PDZ domains. We named this protein S-SCAM (synaptic scaffolding molecule) because S-SCAM may assemble receptors and cell adhesion proteins at synaptic junctions.Effective neurotransmission requires the precise localization of the receptors for neurotransmitters opposite to the presynaptic active zone. The postsynaptic membrane has a dense thickening of submembranous cytoskeleton, called postsynaptic density (PSD) 1 (for review, see Refs. 1 and 2). PSDs play essential roles in the localization of the receptors. Recent studies have identified several molecules that may function in the accumulation and clustering of various receptors at PSDs. PSD-95/SAP90 and its isoforms interact with NMDA receptors and Shaker type potassium channels (3-10), whereas glutamate receptor-interacting protein and Homer interact with ␣-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid and metabotropic glutamate receptors, respectively (11, 12). The common feature for these molecules is that they have a modular PDZ domain for protein-protein interactions (for review, see Refs. 13-16).PDZ domains were originally recognized as the repeats of about 90 amino acids in PSD-95/SAP90 and named after three proteins containing such repeats, PSD-95/SAP90, Drosophila discs-large tumor suppressor protein (Dlg-A), and a tight junction protein, 4,[17][18][19]. The PDZ domains bind to COOH-terminal sequences of various proteins. The first and second PDZ domains of PSD-95/SAP90 interact with NMDA receptors and Shaker type potassium channels (5, 6). PSD-95/ SAP90 is multimerized through the NH 2 -terminal disulfide linkage and clusters these receptors and channels (20). The third PDZ domain of PSD-95/SAP90 binds to the cytoplasmic domain of neuronal cell adhesion molecules, called neuroligins (21).PSD-95/SAP90 has one SH3 domain and one guanylate kinase (GK) domain in addition to the PDZ domains. The SH3 domain was defined as a signaling module in Src ty...

Identification of MAGI1 as a tumor-suppressor protein induced by cyclooxygenase-2 inhibitors in colorectal cancer cells

“…MAGI1 localizes to cell-cell contacts and acts as a scaffold molecule to stabilize cadherin-mediated adhesions and to recruit molecules at cell-cell contacts in endothelial and epithelial cells (Laura et al, 2002). Through its PDZ domains MAGI1 associates with a variety of PDZ-binding molecules such as N-methyl-Daspartate receptors (Hirao et al, 1998), d-catenin (Ide et al, 1999), brain specific angiogenesis inhibitor 1 (BAI-1) (Mino et al, 2000), mNET1 (Dobrosotskaya, 2001), phosphatase and tensin homologue (PTEN) (Kotelevets et al, 2005) and b-catenin (Dobrosotskaya and James, 2000;Kawajiri et al, 2000). In epithelial cells MAGI1 localizes at adherens junctions in complex with b-catenin/ E-cadherin (Dobrosotskaya and James, 2000;Kawajiri et al, 2000) as well as at tight junctions (Ide et al, 1999).…”

MAGUIN, a Novel Neuronal Membrane-associated Guanylate Kinase-interacting Protein

“…Synaptic scaffolding molecule (S-SCAM) was originally identified as a SAPAP-interacting protein (24). We have first reported that S-SCAM has one GK, two WW, and five PDZ domains (24). The GK domain of S-SCAM is shorter than that of PSD-95/SAP90.…”

“…The ligands for other PDZ domains of glutamate receptor-interacting protein have not been so far reported. Synaptic scaffolding molecule (S-SCAM) was originally identified as a SAPAP-interacting protein (24). We have first reported that S-SCAM has one GK, two WW, and five PDZ domains (24).…”

“…We number these PDZ domains consecutively from 0 to 5 (PDZ0, -1, -2, -3, -4, and -5) to keep consistency with the first report. Among six PDZ domains, PDZ1 and -5 bind to the C termini of neuroligin and NMDA receptors, respectively (24). Because S-SCAM has more PDZ domains than PSD-95/SAP90, it may integrate more components of synaptic junctions.…”

Association of synapse‐associated protein 90/ postsynaptic density‐95‐associated protein (SAPAP) with neurofilaments

“…pCMV NMDAR1, pCMV NMDAR2A, and pCMV SAPAP1 were as previously described Hirao et al 1998). The eukaryotic expression constructs of SAPAP are summarized in Fig.…”