Architecture of the heteromeric GluA1/2 AMPA receptor in complex with the auxiliary subunit TARP γ8

Abstract

AMPA-type glutamate receptors (AMPARs) mediate excitatory neurotransmission, and are central regulators of synaptic plasticity, a molecular mechanism underlying learning and memory. Although AMPARs act predominantly as heteromers, structural studies have focused on homomeric assemblies. Here we present a cryo-EM structure of the heteromeric GluA1/2 receptor associated with two TARP γ8 auxiliary subunits, the principal AMPAR complex at hippocampal synapses. Within the receptor, the core subunits arrange to give the GluA2 subunit dominant control of gating. This structure reveals the geometry of the Q/R-site controlling calcium flux, suggests association of TARP-stabilized lipids, and demonstrates that the extracellular loop of γ8 modulates gating by selectively interacting with the GluA2 ligand-binding domain. Collectively, this structure provides a blueprint for deciphering the signal transduction mechanisms of synaptic AMPARs.

Identification of synaptic PPT1 substrates highlight roles of depalmitoylation in disulfide bond formation and synaptic function

“…We have identified that the PPT1 depalmitoylation site for the GluA1 AMPA receptor subunit (GRIA1) is also on the extracellular domain. This extracellular site has not been previously identified, though other palmitoylation sites have been previously identified (Herguedas et al, 2019). The site we identified, (C323) typically forms a disulfide bond (to C75).…”

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.…”

Homomeric Q/R edited AMPA receptors conduct when desensitized

“…These auxiliary proteins determine many biophysical and pharmacological properties of AMPARs and influence their desensitization 23,24 . The prototypical TARP -2 markedly slows the rate of AMPAR desensitization and accelerates recovery from desensitization 25,26 , while TARP -8 and GSG1L slow both the entry into and the recovery from desensitization 21,22,27 . The structures of desensitized complexes, composed of homomeric GluA2 AMPARs with either -2 or GSG1L, have recently been determined at~8 Å resolution by cryo-electron microscopy (cryo-EM) 16,19 .…”