Molecular Mechanisms of Glutamate Receptor Channels

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DESCRIPTION (provided by applicant): We propose to study glutamate receptor-channel (GluR) gating. GluRs mediate the bulk of excitatory neurotransmission in the brain, and the energy required to restore the ionic gradients that run down as a consequence of GluR activation represents a significant fraction of the total energy budget of the organism. NMDA receptors are a subtype of GluR that generate a slow, depolarizing response and that participate in synaptic development and plasticity. NMDA receptor gating occurs as three distinct conformational steps, and the slow synaptic decay arises, to a large extent, from an open state 'trap' that maintains current flow and that keeps the receptor from adopting a conformation from which agonists can dissociate. Moreover, an individual NMDA receptor can generate three distinct gating kinetic modes that arise from fluctuations in the relative stability of the open conformations. We propose to explore the energy landscape for NMDA receptor gating by measuring the effects of perturbations (changes in agonists or mutation of sidechains) on the detailed, single-channel kinetics of the three gating reactions. Our approach is to use linear free energy analysis to reveal the order and organization of molecular motions that occur as the protein traverses the conformational landscape between 'closed' and 'open'. In addition, we propose to probe the gating reaction(s) for a second important class of GluRs, AMPA receptors. Our overall objective is to understand the molecular events that constitute gating of GluRs and to place this information in the context of gating of other synaptic receptors, ion channels, and allosteric proteins. Accordingly, we will better understand the mechanisms by which transmitters, drugs, and other ligands shape the cellular responses of neurons that express these important receptor-channel proteins.