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Show 75 college of science NMDA receptors (NMDARs) are ionotropic glutamate receptors and have been associated with learning and memory and nervous system pathologies. Three of the best-characterized facets of the NMDAR are (1) a Mg2+ dependent voltage-sensitive ion channel block, (2) a glycine requirement for effective channel opening, and (3) Ca2+ permeability. All NMDARs are tetramers of different subunits; at least eight different splice variants for NR1 (A-H) and four different genes for NR2 (A-D), and the subunit composition of a channel is 2NR1.2NR2(A-D.) They also share common structural similarities: large N-terminal region extends into the extracellular space while the C terminus extends into the cytoplasm and two domains in the extracellular segments designated S1 and S2 associate with each other to form the binding site for agonist (Figure 1.) Conantokin-R (Con-R) is a small peptide (27 amino acids) found in the venoms of Conus radiatus that is active as an NMDAR antagonist. There are data that suggest conantokin activity is mediated competitively at the glutamate binding site on the NR2 subunit (Figure 1.) Con-R was shown to potently block NMDA-evoked currents in Xenopus oocytes expressing NR1/NR2B heteromeric receptors but did not block NMDA-evoked currents through NR1/ NR2D subunit combinations (Figure 2.) N-terminal, S1, S2 regions of NMDA receptors in extracellular space are thought to play important roles in ligand binding (Figure 1.) We hypothesized that these regions of NR2 subunits are involved in discriminating between conantokins with differing subtype selectivity. To test this hypothesis, various regions of S1 regions of NR2D were exchanged with corre-sponding regions of NR2B using recombinant DNA methods, and 12 chimera genes were constructed. The properties of the recombinant channels were investigated. Results suggest that NR2B amino acids present in Chimera 11 are important to Con-R sensitivity (Figure 3.) Data also suggest that S2 region may be important for Con-R selectivity. More chimera genes including S2 regions of NR2B subunit with either chimera 11 or 12 genes as a background were constructed (Figure 3.) Based on our data, we hypothesize that a substitution of charged residues at positions 511, 524, and 527 are important for sensitivity (Figure 4.) Complementary experiments using receptors in which residues in NR2D are replaced by those in NR2B are in progress. MAPPING OF CONANTOKIN BINDING SITES ON THE N-METHYL-D-ASPARTATE RECEPTOR Anthony Park (Vernon Twede, Pradip Bandyopadhyay, Baldomero M. Olivera) The Department of Biology University of Utah UNDERGRADUATE RESEARCH ABSTRACTS |
