Architecture and subunit arrangement of native AMPA receptors elucidated by cryo-EM

Abstract

Glutamate-gated AMPA receptors mediate the fast component of excitatory signal transduction at chemical synapses throughout all regions of the mammalian brain. AMPA receptors are tetrameric assemblies composed of four subunits, GluA1–GluA4. Despite decades of study, the subunit composition, subunit arrangement, and molecular structure of native AMPA receptors remain unknown. Here we elucidate the structures of 10 distinct native AMPA receptor complexes by single-particle cryo–electron microscopy (cryo-EM). We find that receptor subunits are arranged nonstochastically, with the GluA2 subunit preferentially occupying the B and D positions of the tetramer and with triheteromeric assemblies comprising a major population of native AMPA receptors. Cryo-EM maps define the structure for S2-M4 linkers between the ligand-binding and transmembrane domains, suggesting how neurotransmitter binding is coupled to ion channel gating.

A new mouse line with reduced GluA2 Q/R site RNA editing exhibits loss of dendritic spines, hippocampal CA1-neuron loss, learning and memory impairments and NMDA receptor-independent seizure vulnerability

“…AMPARs are tetrameric protein complexes composed of differing combinations of four subunits, denoted GluA1-GluA4 (also known as GluR1-4 and GluRA-D, for a full review of AMPAR architecture refer here [2]). Diversity of AMPARs is created through several mechanisms including differing subunit composition [3][4][5][6], posttranslational modifications [7,8], alternative splicing [9] and a process known as RNA editing [10][11][12], all of which can profoundly alter AMPAR properties.…”

“…R). The editing-induced amino acid change has a profound impact: AMPARs containing edited GluA2(R) (which appear to constitute a majority of total AMPARs physiologically [4][5][6]16]) are Ca 2+ -impermeable. This likely occurs because the arginine is positively charged and present in the pore-lining (M2) region [17] which, in contrast to the uncharged glutamine, prevents Ca 2+ flux.…”

Structural and functional insights into transmembrane AMPA receptor regulatory protein complexes

“…While the recent wealth of structural information on TARP/TARP-like complexes (Twomey et al, 2016, 2017a,b, 2018; Zhao et al, 2016, 2019; Chen et al, 2017; Herguedas et al, 2019) and claudins (Suzuki et al, 2014; Saitoh et al, 2015; Nakamura et al, 2019) has provided new insights into potential modulatory interfaces, the exact interactions are in fact ambiguous. The loops are often only visible at low thresholds in cryo-EM density maps, indicating that the loops are conformationally heterogeneous in the states that have been captured in structural studies and are not tightly bound.…”

“…Recent proteomics studies have identified >30 AMPAR regulatory proteins, which are structurally and functionally diverse (Schwenk et al, 2012; Shanks et al, 2012). In this review, we focus on the structure and function of claudin-fold auxiliary subunits, including TARPs, and advances in understanding their modulation of AMPAR function associated with recent developments in cryo-EM (Twomey et al, 2016, 2017a,b, 2018; Zhao et al, 2016, 2019; Chen et al, 2017; Herguedas et al, 2019). TARPs assemble around AMPARs at variable stoichiometry (Shi et al, 2009; Kim et al, 2010; Hastie et al, 2013; Twomey et al, 2016) but appear to share conserved assembly interfaces along the AMPAR TMD.…”

A comprehensive study of the voltage gated potassium channel Kv4.3: from functional analysis to molecular dynamics modelling

“…An alternative technique, which does not require the formation of crystals, has come to the forefront in the past few years: cryo-electron microscopy (cryo-EM). This technique has been used to solve the structure of different ion channels, such as the transient receptor potential (TRP) channel, whose structure had never been crystallized in its whole length, and other channels, such as the calciumactivated chloride channel TMEM16A, the Orai channel and the glutamate AMPA receptor Liu et al, 2019;Paulino, Kalienkova, Lam, Neldner, & Dutzler, 2017;Zhao, Chen, Swensen, Qian, & Gouaux, 2019). However, the drawback of cryo-EM is that it cannot be used on low molecular weight complexes (i.e., approximately 100 kDa).…”