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.
SourceAvailable from: Werner Baumgartner[Show abstract] [Hide abstract]
ABSTRACT: Synapses in the central nervous system (CNS) are highly dynamic structures that undergo reorganisation in response to synaptic activity. Dysfunctional structural synaptic plasticity is associated with impaired brain function and several neurological disorders. As response to synaptic activity, dendritic spines of excitatory synapses were reported to undergo alterations in their molecular structure and morphology leading to increased postsynaptic density size and spine volume. For these structural changes a transient activity-dependent weakening of synaptic adhesion will be necessary. Here, we report that zinc can modulate N-cadherin-mediated adhesion. Quantification of binding activity was performed using laser tweezer technique. Our results show that increased levels of zinc abolished N-cadherin binding without altering the number of N-cadherin molecules expressed at the cell surface. Furthermore, zinc directly interacted with N-cadherin and the regulatory role was found to take place under physiological zinc concentrations within minutes. Given that zinc is released at zincergic synapses in the CNS, our findings may contribute to mechanistic insights in the interplay between zinc signalling, activation of glutamate receptors and downstream pathways, and the coordination of pre- and postsynaptic changes via trans-synaptic cell adhesion complexes, all finally contributing to synaptic plasticity.Metallomics 01/2015; 7(2). DOI:10.1039/C4MT00300D · 3.98 Impact Factor
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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). DOI:10.1113/jphysiol.2014.284448 · 4.54 Impact Factor
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ABSTRACT: NMDA receptors (NMDAR) are voltage- and glutamate-gated heteromeric ion channels found at excitatory neuronal synapses, the functions of which are to mediate the mechanisms of brain plasticity and, thereby, its higher order functions. In addition to Glu, the activation of these heteromeric receptors requires Gly or D-Ser as a coagonist. However, it is not fully known as to why coagonism is required for the opening of NMDAR ion channels. We show herein that the ligand binding domains (LBD) of the GluN1 and GluN2A subunits of the NMDAR heterodimerize only when both coagonists, Glu and Gly/D-Ser, bind to their respective sites on GluN2 and GluN1. In the agonist-free state, these domains form homomeric interactions, which are disrupted by binding of their respective agonists. Also, in a heteromer formed by the LBDs, GluN2A is more sensitized to bind Glu, while the affinity of Gly for GluN1 remains unchanged. We thus provide direct evidence to show that coagonism is necessary for heteromeric pairing of LBDs, which is an essential step in forming functional ion channels in NMDARs.Biochemistry 12/2014; DOI:10.1021/bi501437s · 3.19 Impact Factor