Activation and desensitization mechanism of AMPA receptor-TARP complex by cryo-EM

Abstract

SummaryAMPA receptors mediate the majority of fast excitatory neurotransmission in the mammalian brain and transduce the binding of presynaptically released glutamate to the opening of a transmembrane cation channel. Within the postsynaptic density, however, AMPA receptors coassemble with transmembrane AMPA receptor regulatory proteins (TARPs), yielding altered gating kinetics, receptor pharmacology and pore properties.Here we elucidate full-length GluA2-TARP γ2 complex structures in the presence of the partial agonist kainate or the full agonist quisqualate together with a positive allosteric modulator, and with quisqualate alone. We show how TARPs sculpt the ligand binding domain gating ring, enhancing kainate potency and diminishing the ensemble of desensitized states. The 4 TARPs encircle receptor ion channel, stabilizing M2 helices and pore loops, thus showing how TARPs alter receptor pore properties. Structural and computational analysis suggests the full agonist/modulator complex harbors an ionpermeable channel gate, thus providing the first view of an activated AMPA receptor.All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint (which . http://dx.doi.org/10.1101/158402 doi: bioRxiv preprint first posted online page 3In the mammalian central nervous system the majority of fast excitatory neurotransmission is initiated by -amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-sensitive ionotropic glutamate receptors in complex with modulatory auxiliary subunits (Jackson and Nicoll, 2011;Traynelis et al., 2010). Transmembrane AMPA receptor regulatory proteins (TARPs) (Chen et al., 2000), the most widespread and well studied family of auxiliary proteins, alter AMPA receptor gating kinetics, ion channel properties and pharmacology (Milstein and Nicoll, 2008). The prototypical TARP, deemed stargazin or TARP 2, potentiates AMPA activity by decelerating deactivation and desensitization kinetics, facilitating recovery from desensitization, boosting the efficacy of partial agonists, and attenuating polyamine block (Milstein et al., 2007;Soto et al., 2007;Tomita et al., 2005).AMPA receptors have a modular architecture with synaptically localized amino terminal domains (ATDs) and ligand binding domains (LBDs), an ion channel forming transmembrane domain (TMD) and a largely unstructured cytoplasmic domain (CTD) (O'Hara et al., 1993;Soderling and Derkach, 2000;Stern-Bach et al., 1994;Wo and Oswald, 1995;Wollmuth and Sobolevsky, 2004). Extensive studies on isolated receptor domains and intact receptors have illuminated, at high resolution, how agonists induce local 'clamshell' closure of the LBDs and how the LBDs are arranged as nonequivalent pairs of A/C and B/D dimers within an overall 2-fold symmetric LBD 'gating ring' (Armstrong and Gouaux, 2000;Jin et al., 2009;Kuusinen et al., 1999;Sobolevsky et al., 2009;Sun et al., 2002). Although crystallograp...

Non-selective cation permeation in an AMPA-type glutamate receptor

“…The dashed line shows the fitted chord conductance, which for this patch was 33 pS. simultaneously enter the inner mouth of the region, classically expected to be part of the SF 141 (2,24), and composed by the residues G588, C589 and D590. K + and Na + paused frequently 142 but briefly at a secondary site (which we denote SII) which is positioned around 10 Å into the 143 pore, cytoplasmic to the SI site ( Figure 3B).…”