NMDA receptors have received a great deal of attention because of their role in synaptic plasticity, seizure initiation, and ischemia-induced neuronal death. Recent crystallographic advances have provided the first structure for the agonist binding domains of NR1 and NR2A subunits, and recent functional studies have provided the first conceptual models of NR1/NR2A receptor activation that account for both single channel and macroscopic properties. These advances create an ideal opportunity to explore in detail the relationship between structure and function for NMDA receptors. We will evaluate function in the context of structure for NR1/NR2C and NR1/NR2D receptors, which remain poorly understood despite their roles in striatal and cerebellar function and the intriguing therapeutic potential of NR2C/NR2D subunit-selective modulators. The proposed experiments exploit our recent success in obtaining outside-out membrane patches that contain only one active channel to examine the function of NR1/NR2C and NR1/NR2D receptors activated by both glutamate and novel subunit-selective agonists and modulators. Single channel studies will be extended to native NR2D-containing receptors and recombinant heterotrimeric receptors containing two different NR2 subunits, which can be unambiguously isolated in one channel patches. Complementary experiments will exploit structural data by using atomic co-variance analysis of molecular dynamics simulations of the agonist binding domains for all NR1/NR2 combinations to evaluate long-range intra-protein motions. Our preliminary data reveal intra-protein motions that show domain closure, a pivot around the NR1/NR2 dimer interface, and different interdomain contacts between functionally dissimilar NR2A and NR2D. Understanding the relationship between structure and function is a pre-requisite to rational drug design, which may ultimately yield therapeutically relevant compounds. Proposed experiments will address four questions. 1. How do the NR2C and NR2D subunits control NMDA receptor activation? 2. What are the functional properties of heterotrimeric NR1/NR2A/NR2D and NR1/NR2B/NR2D receptors? 3. How does the NR2D subunit control native NMDA receptor activation? 4. What structural features of the NR1/NR2 dimer influence intra-protein motion and receptor activation?
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