| NMDA receptors represent a very important class of receptors that can be activated by the neurotransmitter glutamate. These receptors play a major role in long-term potentiation, memory formation, and neuronal degeneration. NMDA receptors consist of NMDAR1, NMDAR2A-2D, and NMDAR3. Our laboratory identified an NMDA receptor-like complex comprised of different proteins from NMDAR1-R3. These are a glutamate-binding protein (GBP), a (±)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP)-binding protein CPP-BP), a glycine-binding protein GIyBP, and an N-[1-(2-thienyl)cyclohexyl]piperidine (TCP)-binding protein (TCP-BP). In the present study, polyclonal antibodies against the native GlyBP subunit of rat brain have been generated and used to study the structure and function of the NMDA receptor-like complex. Immunohistochemical and biochemical studies were carried out using the polyclonal antibodies for GlyBP together with those for two other subunits, GBP and CPPBP. The results from studies of immunohistochemical localization indicated that GlyBP, GBP, and CPPBP distributed in brain regions known to have glutamatergic neurotransmission. Within those regions, the three proteins were expressed in neurons, and in particular in cell bodies and dendrites of neurons. Co-immunoprecipitation experiments demonstrated the association of GlyBP with GBP and CPPBP, but not with either NR1 or NR2. Therefore, NMDA receptor proteins did not appear to interact with those of the receptor-like complex. In the studies of NMDA-induced toxicity and NMDA-induced currents in hippocampal neurons, the anti-GlyBP antibodies protect neurons from NMDA-induced neurotoxicity and partially inhibited NMDA-induced currents. The latter inhibition was specific not only for NMDA-induced currents but also for immune IgG against the GlyBP. Based on the lack of interaction between GlyBP and NMDAR1/R2 the effects of the anti-GIyBP antibodies on cell viability and currents were indicative of a receptor-like function for the complex of proteins that includes GlyBP. |
