Activation and Desensitization Mechanism of AMPA Receptor-TARP Complex by Cryo-EM

Abstract

Summary AMPA receptors mediate 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 a receptor complex with altered gating kinetics, pharmacology and pore properties. Here we elucidate structures of the GluA2-TARP γ2 complex in the presence of the partial agonist kainate or the full agonist quisqualate together with a positive allosteric modulator, or with quisqualate alone. We show how TARPs sculpt the ligand binding domain gating ring, enhancing kainate potency and diminishing the ensemble of desensitized states. TARPs encircle the receptor ion channel, stabilizing M2 helices and pore loops, illustrating how TARPs alter receptor pore properties. Structural and computational analysis suggests the full agonist/modulator complex harbors an ion-permeable channel gate, providing the first view of an activated AMPA receptor.

Mechanism of modulation of AMPA receptors by TARP-γ8

“…A large number of structures are available for the AMPA receptor in various liganded conditions, in addition to structures of the receptor in the presence of the auxiliary protein γ2 (Dürr et al, 2014;Sobolevsky et al, 2009;Yelshanskaya et al, 2014;Zhao et al, 2016;Twomey et al, 2016;Twomey et al, 2017;Chen et al, 2017;Meyerson et al, 2014). In addition, spectroscopic and biochemical investigations have provided a map of the conformational and functional landscape of the receptor under these conditions (Gonzalez et al, 2008;Gonzalez et al, 2010;Ramaswamy et al, 2012;MacLean et al, 2014).…”

Small-angle neutron scattering studies on the AMPA receptor GluA2 in the resting, AMPA-bound and GYKI-53655-bound states

“…Methods to study the structures of ionotropic glutamate receptors are essential in order to understand how these receptors function as well as to understand their roles in diseases and as targets for medicines. In recent years, the AMPA receptor GluA2 has been thoroughly characterized in the resting, activated and desensitized states using X-ray crystallography and cryo-EM (see, for example, Dü rr et al, 2014;Twomey et al, 2017a,b;Chen et al, 2017). In this study, we investigated GluA2 in solution at 10 C using SANS.…”

“…Recently, the first structures of GluA2 in the activated state and in the desensitized state (an inactive form of the receptor where glutamate is still bound) have been reported using cryo-electron microscopy (cryo-EM; Twomey et al, 2017a,b). To date, approximately 40 full-length GluA2 structures have been deposited in the Protein Data Bank (PDB; http://www.rcsb.org), of which half were determined by X-ray crystallography (Sobolevsky et al, 2009;Chen et al, 2014;Dü rr et al, 2014;Yelshanskaya et al, 2014Yelshanskaya et al, , 2016 and the other half by electron microscopy (Meyerson et al, 2014;Twomey et al, 2016Twomey et al, , 2017aZhao et al, 2016;Chen et al, 2017). As can be seen in Fig.…”

Structural Mechanisms of Gating in Ionotropic Glutamate Receptors

“…Consistent with this idea, incompletely closed clamshells are easier to capture in structures with partial agonists, especially if these structures are stabilized by crystal contacts or complexes with auxiliary subunits. 13 , 16 , 49 …”