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The Split Personality of Glutamate Transporters: A Chloride Channel and a Transporter

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Abstract

Transporters and ion channels are conventionally categorised into distinct classes of membrane proteins. However, some membrane proteins have a split personality and can function as both transporters and ion channels. The excitatory amino acid transporters (EAATs) in particular, function as both glutamate transporters and chloride (Cl−) channels. The EAATs couple the transport of glutamate to the co-transport of three Na+ ions and one H+ ion into the cell, and the counter-transport of one K+ ion out of the cell. The EAAT Cl− channel is activated by the binding of glutamate and Na+, but is thermodynamically uncoupled from glutamate transport and involves molecular determinants distinct from those responsible for glutamate transport. Several crystal structures of an EAAT archaeal homologue, GltPh, at different stages of the transport cycle, alongside numerous functional studies and molecular dynamics simulations, have provided extensive insights into the mechanism of substrate transport via these transporters. However, the molecular determinants involved in Cl− permeation, and the mechanism by which this channel is activated are not entirely understood. Here we will discuss what is currently known about the molecular determinants involved in EAAT-mediated Cl− permeation and the mechanisms that underlie their split personality.

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Acknowledgments

R.J.C. is supported by an Australian Postgraduate Award and a John Lamberton scholarship. This work is supported by a National Health and Medical Research Council Project Grant (#1048784) to R.M.R. and R.J.V.

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  1. Discipline of Pharmacology, School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, NSW, 2006, Australia

    Rosemary J. Cater, Renae M. Ryan & Robert J. Vandenberg

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  1. Rosemary J. Cater
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  2. Renae M. Ryan
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  3. Robert J. Vandenberg
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Correspondence to Renae M. Ryan or Robert J. Vandenberg.

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Special Issue: In honor of Philip Beart.

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Cater, R.J., Ryan, R.M. & Vandenberg, R.J. The Split Personality of Glutamate Transporters: A Chloride Channel and a Transporter. Neurochem Res 41, 593–599 (2016). https://doi.org/10.1007/s11064-015-1699-6

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