Structural conformations of kainate receptors in physiology and pathophysiology

• Applicant: Patricia Brown, Ph.D.
• Subject Area: Structural Biology ; Molecular Biology and Physiology of Neurons and Glial Cells ; Molecular and Cellular Neurology and Neuropathology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 516425236

Ionotropic glutamate receptors (iGluRs) mediate fast excitatory neurotransmission in the mammalian central nervous system (CNS). While AMPA- and NMDA-type iGluRs play important roles in synaptic plasticity, kainate-type iGluRs (KARs) modulate neuronal circuits. Mice lacking all KAR genes (Grik) exhibit motor deficits and severe compulsive behaviours, which are correlated with anatomical and synaptic functional deficits in neuronal circuits. In humans, de novo loss-of-function and gain-of-function variants in the GRIK genes have been associated with neurological and neurodevelopmental disorders including intellectual disability, movement disorders and epilepsy. Therefore, KARs represent an important class of potential therapeutic targets and it is crucial to understand the architectural and functional properties governing their behaviour. Native KARs are thought to assemble as heteromeric complexes formed of primary and secondary subunits, each of which endows the receptor with unique functional properties. KAR desensitization is accompanied by extensive conformational changes in the ligand-binding domain (LBD), a feature that differentiates them structurally from other iGluRs. Specifically, the complete rupture of the LBD dimer following agonist binding results in receptor desensitization. Previously, studies examining mutations in the GluK2 subunit LBD established that the stability of the LBD dimer plays a major role in regulating receptor desensitization. For this project, I propose to use cryo-electron microscopy (cryo-EM) to investigate the structural impact of a non-desensitizing GluK2 mutant, namely D776K, in the context of full-length homomeric and heteromeric receptors. More specifically, this structural information will reveal how conformational changes in the LBD and channel pore lead to ion flux in the open conformation, which to date remains unknown for KARs. Furthermore, naturally-occurring gain-of-function variants in the GRIK2 gene are associated with severe neurodevelopmental disorders and bestow constitutive activity to the receptors. Here, I propose to examine the impact of the gain-of-function variant A657T on the structure of homomeric and heteromeric KARs using cryo-EM, in order to determine the precise conformational or architectural changes in the channel pore that lead to ion flux in the absence of ligand binding. In turn, this information could be very useful for the development of targeted therapeutic approaches in the future.

• DFG Programme: Research Grants