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Summer Research Fellowship Programme of India's Science Academies

Ionotropic Glutamate receptors: Cloning, expression and functional studies of Clinically significant Mutations

Diksha Kumari

The Maharaja Sayajirao University of Badoda, Vadodara (Gujarat), 390020

Dr. Janesh Kumar

National Centre for Cell Sciences, SP Pune University Campus, Pune (Maharashtra), 411007

Abstract

The functioning of nervous systems is pivoted on transmission at synapses and converting chemical signals into electrical ones, and vice-a-versa. Ionotropic glutamate receptors are ligand-gated, non-selective cation channels that play key roles in this process. They bind to the neurotransmitter glutamate, that acts as an endogenous ligand for these channels, to mediate fast excitatory synaptic transmission in the central nervous system. There are four different classes of ionotropic glutamate receptors based upon the name of the drugs that that bind to them and sequence homology, namely AMPA receptors (GluA1-GluA4), kainate receptors (GluK1-GluK5), NMDA receptors (GluN1,GluN2A-GluN2D, GluN3A and GluN3B) and delta receptors (GluD1 and GluD2). Each glutamate receptor is a tetramer made of four structurally different domains- amino terminal domain (ATD), ligand binding domain (LBD), transmembrane domain (TM) and carboxy terminal domain (CTD). It has been shown in different studies conducted previously that patients with some neurological disorders like perturbed sleep patterns, intellectual disability, autism etc, have mutations in various ionotropic glutamate receptor genes. The present study is focused on the GluK2 receptor which belongs to the kainate receptor family. Clinically significant missense Single Nucleotide Polymorphisms (SNPs) were selected for GluK2 from NCBI SNP database. The selected mutations were mapped on full-length hGluK2 structure (PDB ID5KUF) and it was found that most of them were present in either its amino terminal domain (ATD) or ligand-binding domain (LBD). The major objective of the present study is in-vitro electrophysiological profiling (important ion channel kinetic properties such as activation, desensitization, recovery from desensitization, steady state currents) of SNPs-harboring iGluRs expressed heterologously in HEK293 cells to investigate the functional and structural changes that occur in ligand-receptor interactions and ligand evoked receptor responses. Rat GluK2 was used as a template to generate human GluK2 equivalent. Introducing selected SNPs in human GluK2 template is under process.

 Keywords: Synapses, missense SNP, Neurotransmission, Kainate receptors, Electrophysiology, Therapeutics

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