Molecular regulation of Kainate receptors

PROJECT SUMMARY/ABSTRACT Kainate receptors (KARs) are a type of ionotropic glutamate receptors (iGluRs) found in the mammalian central nervous system (CNS). These receptors mediate excitatory neurotransmission, which is essential for normal brain function. Native KARs form heteromeric complexes consisting of primary (GluK1-3) and secondary (GluK4- 5) subunits, each contributing unique functional characteristics to KARs. In humans, perturbation in KAR functions or novel genetic variations causing either loss or gain of function in KAR subunits have been associated with neurological and neurodevelopmental disorders, such as intellectual disability, movement disorders, and epilepsy. Consequently, KARs represent a set of potential targets for therapeutic interventions, and it is imperative to gain a deep understanding of the structural and functional characteristics that govern the behavior of KARs. So far, the structural details about the open state of KARs are unavailable; hence, the mechanism of ion permeation through KARs remains poorly understood. However, the Cryo-electron microscopy (cryo-EM) structures of KARs showed that ligand binding domain (LBD) in the desensitized state of KARs separate from each other, compared to other iGluRs, indicating that LBDs in KARs are susceptible to dissociation in continuous presence of agonist. Therefore, this research proposes to investigate the structural aspects of KARs using a (Aim 1) non-desensitizing mutant GluK2-D776K and (Aim 2) a de novo gain-of-function variant GluK2-A657T using cryo-EM. The GluK-D776K is expected to stabilize the LBD to facilitate the capture of the open state of KAR. In contrast, GluK2-A657T results in the constitutive activity or the 'channel leakiness' without ligand binding and is associated with ataxia, speech, and mental disabilities. The expected outcome of this proposal will uncover the architectural and conformational changes in KARs and the mechanism of ion permeation through KARs in an agonist-dependent and independent manner. The obtained structural insights will also facilitate the design of selective KAR inhibitors for neurological disorders.