A Novel NE-dlg/SAP102-associated Protein, p51-nedasin, Related to the Amidohydrolase Superfamily, Interferes with the Association between NE-dlg/SAP102 and N-Methyl-d-aspartate Receptor

Abstract

The membrane-associated guanylate kinase proteins have been known to interact various membrane receptors with their N-terminal segments designated the PDZ domains and to cluster these receptors at the target site of the cell membrane. NE-dlg/SAP102, a neuronal and endocrine tissue-specific MAGUK family protein, was found to be expressed in both dendrites and cell bodies in neuronal cells. Although NE-dlg/SAP102 localized at dendrites was shown to interact with N-methyl-D-aspartate receptor 2B via the PDZ domains to compose postsynaptic density, the binding proteins existing in the cell body of the neuron are still unknown. Here we report the isolation of a novel NE-dlg/SAP102-associated protein, p51-nedasin. Nedasin has a significant homology with amidohydrolase superfamily proteins and shows identical sequences to a recently identified protein that has guanine aminohydrolase activity. Nedasin has four alternative splice variants (S, V1, V2, and V3) that exhibited different C-terminal structures. NE-dlg/ SAP102 is shown to interact with only the S form of nedasin which is predominantly expressed in brain. The expression of nedasin in neuronal cells increases in parallel with the progress of synaptogenesis and is mainly detected in cell bodies where it co-localizes with NE-dlg/ SAP102. Furthermore, nedasin interferes with the association between NE-dlg/SAP102 and NMDA receptor 2B in vitro. These findings suggest that alternative splicing of nedasin may play a role in the formation and/or structural change in synapses during neuronal development by modifying clustering of neurotransmitter receptors at the synaptic sites.At the sites of cell-cell contacts of epithelial cells or the synaptic junctions of neuronal cells, several membrane receptors and channels are clustered into multiprotein complexes linked to the cytoskeleton via interactions of their C-terminal cytoplasmic tails with a novel protein family called membraneassociated guanylate kinase homologues (MAGUK) 1 (1). The MAGUK family proteins contain three distinct domains as follows: an N-terminal segment comprised of one or three copies of an 80 -90-amino acid motif called the PDZ (PSD-95/Dlg/ ZO-1) domain, an src homology 3 (SH3) domain, and a region with high similarity to guanylate kinases (GK) (2, 3). The PDZ domain is utilized as a module for interacting with the Cterminal Xaa-(Ser/Thr)-Xaa-Val (X(S/T)XV) motif of various proteins and generating multiprotein complexes (4, 5).Each MAGUK protein is thought to perform a distinct function depending upon its tissue distribution, cellular localization, and associated molecules. For instance, PSD-95/SAP90, which is one of the MAGUK proteins, is predominantly expressed in the brain and localizes at the postsynaptic membrane and presynaptic axon terminals of inhibitory neurons (6 -8). PSD-95/SAP90 binds to the cytoplasmic tail of both Shaker-type voltage-gated K ϩ channels and the 2B subunit of N-methyl-D-aspartate (NMDA)-type glutamate receptors (7, 9 -11). PSD-95/SAP90 expressed in neuronal cells is therefo...

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