Zinc Potentiates GluK3 Glutamate Receptor Function by Stabilizing the Ligand Binding Domain Dimer Interface.
ABSTRACT Kainate receptors (KARs) play a key role in the regulation of synaptic networks. Here, we show that zinc, a cation released at a subset of glutamatergic synapses, potentiates glutamate currents mediated by homomeric and heteromeric KARs containing GluK3 at 10-100 μM concentrations, whereas it inhibits other KAR subtypes. Potentiation of GluK3 currents is mainly due to reduced desensitization, as shown by kinetic analysis and desensitization mutants. Crystallographic and mutation analyses revealed that a specific zinc binding site is formed at the base of the ligand binding domain (LBD) dimer interface by a GluK3-specific aspartate (Asp759), together with two conserved residues, His762 and Asp730, the latter located on the partner subunit. In addition, we propose that tetrameric GluK2/GluK3 receptors are likely assembled as pairs of heterodimeric LBDs. Therefore, zinc binding stabilizes the labile GluK3 dimer interface, slows desensitization, and potentiates currents, providing a mechanism for KAR potentiation at glutamatergic synapses.
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ABSTRACT: It has been about 25 years since a landmark cloning study identified the molecular identity of the first of 18 different genes that encode the ionotropic glutamate receptor (iGluR) family (Hollmann et al. 1989). Since that time, we have witnessed major advances in our understanding of the biology of iGluRs. Breakthroughs in genetics provided our first insights into the many roles iGluRs fulfil in behaviour and disease (Mulle et al. 1998), with advances in biochemistry identifying the myriad of protein partners that shuttle iGluRs into and out of synapses (Nicoll et al. 2006; Sheng & Kim, 2011). The last decade has been dominated by structural biology, which has offered an unprecedented glimpse into the working life of the iGluR at atomic resolution (Gouaux, 2004; Mayer & Armstrong, 2004). Each great advance has drawn more and more distinct scientific disciplines into the iGluR field, making it a challenge to keep up with the latest technological developments and biological advances. With this in mind, a group of iGluR aficionados looked for ways to bring the iGluR community together to enhance trainee development and bring greater collaboration amongst the disciplines. The solution was to hold an annual iGluR Retreat on a university campus within reach by car to minimize cost. With so many iGluR researchers residing within the northeast quadrant of North America, the idea was met with great enthusiasm. The inaugural iGluR Retreat was held on the campus of Cornell University in August 2013 organized by Dr. Linda Nowak and Robert Oswald (see Fig. 1), with Dr Gabriela Popescu hosting the 2014 Retreat at SUNY Buffalo. This issue of The Journal of Physiology brings together seven timely review articles that capture some of the new ideas, discussions and debates that arose during these meetings.The Journal of Physiology 01/2015; 593(1). · 4.38 Impact Factor
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ABSTRACT: The kainate receptors are the least studied subfamily of ionotropic glutamate receptors. These receptors are thought to have a neuromodulatory role and have been associated with a variety of disorders in the central nervous system. This makes kainate receptors interesting potential drug targets. Today, structures of the ligand binding domain (LBD) of the kainate receptor GluK3 are only known in complex with the endogenous agonist glutamate, the natural product kainate, and two synthetic agonists. Herein we report structures of GluK3 LBD in complex with two 2,4-syn-functionalized (S)-glutamate analogues to investigate their structural potential as chemical scaffolds. Similar binding affinities at GluK3 were determined for the 2-(methylcarbamoyl)ethyl analogue (Ki=4.0 μM) and the 2-(methoxycarbonyl)ethyl analogue (Ki=1.7 μM), in agreement with the similar positioning of the compounds within the binding pocket. As the binding affinity is similar to that of glutamate, this type of Cγ substituent could be used as a scaffold for introduction of even larger substituents reaching into unexplored binding site regions to achieve subtype selectivity.ChemMedChem 07/2014; 9(10). · 3.05 Impact Factor
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ABSTRACT: The divalent cation, zinc is the second most abundant metal in the human body and is indispensable for life. Zinc concentrations must however, be tightly regulated as deficiencies are associated with multiple pathological conditions while an excess can be toxic. Zinc plays an important role as a cofactor in protein folding and function, e.g. catalytic interactions, DNA recognition by zinc finger proteins and modulation ion channel activity. There are 24 mammalian proteins specific for zinc transport that are subdivided in two groups with opposing functions: ZnT proteins reduce cytosolic zinc concentration while ZIP proteins increase it. The mammalian brain contains a significant amount of zinc, with 5-15% concentrated in synaptic vesicles of glutamatergic neurons alone. Accumulated in these vesicles by the ZnT3 transporter, zinc is released into the synaptic cleft at concentrations from nanomolar at rest to high micromolar during active neurotransmission. Low concentrations of zinc modulate the activity of a multitude of voltage- or ligand-gated ion channels, indicating that this divalent cation must be taken into account in the analysis of the pathophysiology of CNS disorders including epilepsy, schizophrenia and Alzheimer's Disease. In the context of the latest findings, we review the role of zinc in the central nervous system and discuss the relevance of the most recent association between the zinc transporter, ZIP8 and schizophrenia. An enhanced understanding of zinc transporters in the context of ion channel modulation may offer new avenues in identifying novel therapeutic entities that target neurological disorders.Biochemical Pharmacology 08/2014; · 4.65 Impact Factor