Ligand-gated ion channels mediate information transfer at synapses. The binding of neurotransmitter molecules to the ligand-binding domains (LBDs) of these channels drive the opening of transmembrane pores, allowing cations to flow across the cell membrane to trigger the generation of a nerve impulse in the postsynaptic neuron. The site of agonist binding is usually distant from the transmembrane pore, so activation of the channel must be mediated by allosteric coupling of conformational changes at the binding site to corresponding changes at the channel's gate. The ionotropic glutamate receptor ion channels (iGluRs) mediate excitatory responses at the vast majority of synapses in the brain and spinal cord. A growing body of evidence indicates that iGluRs have key roles in a broad variety of neurodegenerative and psychiatric diseases, which makes them important targets for therapeutic intervention. iGluRs are divided into four major families, the AMPA, kainate, NMDA, and delta receptors. These receptors assemble as tetramers. The available crystal structures of the LBDs are very informative, but they can only provide a static view of the most stable conformational state of the system. We have designed a joint computational and experimental study to extend our knowledge of the atomic and molecular factors responsible for iGluR regulation. We will (1) characterize the process of ligand-binding for a set of ligands to the AMPA, kainate, and NMDA receptor LBDs using free energy computations and experimental measurements, (2) characterize LBD-LBD dimer rearrangements that underlie desensitization for the AMPA, kainate, and NMDA receptors using free energy computations, (3) measure solution X-ray scattering from LBD monomers, tethered dimers, and crosslinked tetramers to compare with the predicted conformational populations, and (4) try to crystallize crosslink-stabilized LBD tetramers and a stabilized LBD-pore assembly.
We propose a research project to understand the atomic and molecular factors that regulate "neuroreceptor" proteins called glutamate receptors. These proteins have key roles in neurodegenerative and psychiatric diseases. The research will help better understand the action of drugs targeting glutamate receptors.
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