High-Level Expression of Human EAAT3 for Biochemical and Structural Analysis

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DESCRIPTION (provided by applicant): Glutamate is released by presynaptic neurons and stimulates an electrical signal in postsynaptic neurons. In order for recurrent signaling to occur, the neurotransmitter must be removed from the synapse soon after release. In the normal brain, glutamate is efficiently removed by glutamate transporters, known as excitatory amino acid transporters (EAATs). These molecules are found on the surface of neurons and other brain cells. In abnormal states, however, high amounts of glutamate can lead to overexcitation of the receiving nerve cell, resulting in damage or death. This process, known as glutamate excitotoxicity, is thought to contribute to neuronal loss seen in cerebral ischemia and head trauma, and is involved in neurodegenerative conditions such as Huntington's and Alzheimer's diseases. Therefore, treatments aimed at returning glutamate transporters to normal levels of expression and function may be therapeutic. Both antagonists and agonists of EAATs could be neuroprotective under certain conditions, and so development of such compounds is of significant biomedical importance. Development of effective inhibitors is impeded by lack of a recombinant expression system for EAAT3. Current methods to assay the transporter activity of EAATs are cumbersome, and the lack of high-resolution structural information for mammalian EAAT3 makes rational inhibitor design challenging. The goal of this project is to develop an insect cell expression system to produce pure, active human EAAT3 as a stable detergent complex in milligram quantities. The purified protein will be used for ligand screening, biophysical characterization and crystallization for high resolution X-ray structure determination. A novel fluorescence-based assay will be created, based on site-directed mutants of EAAT3, to measure binding activity in a microplate format for screening of glutamate transporter inhibitors synthesized at the University of Montana. A variety of experimental approaches will be taken to produce and optimize crystals of EAAT3 suitable for high-resolution structural analysis, in order to elucidate the mechanism of human EAAT3 transport activity and facilitate the design of compounds to block glutamate excitotoxicity. PUBLIC HEALTH RELEVANCE: In stroke, head trauma, Huntington's and Alzheimer's diseases, levels of glutamate become too high, causing the permanent loss of neurons. In the normal brain, glutamate levels are kept low by glutamate transporters, known as excitatory amino acid transporters (EAATs). This research will help explain how these proteins work and possibly aid in the development of new drugs that will help prevent the effects of high glutamate.