Modulatory mechanisms of TARP γ8-selective AMPA receptor therapeutics

Abstract

AMPA glutamate receptors (AMPARs) mediate excitatory neurotransmission throughout the brain. Their signalling is uniquely diversified by brain region-specific auxiliary subunits, providing an opportunity for the development of selective therapeutics. AMPARs associated with TARP γ8 are enriched in the hippocampus, and are targets of emerging anti-epileptic drugs. To understand their therapeutic activity, we determined cryo-EM structures of the GluA1/2-γ8 receptor associated with three potent, chemically diverse drugs. We find that despite sharing a lipid-exposed and water-accessible binding pocket, drug action is differentially affected by binding-site mutants. Together with patch-clamp recordings and MD simulations we demonstrate that ligand-triggered reorganisation of the AMPAR-TARP interface contributes to modulation. Unexpectedly, one ligand (JNJ-61432059) acts bifunctionally, negatively affecting GluA1 but exerting positive modulatory action on GluA2-containing AMPARs, in a TARP stoichiometry-dependent manner. These results further illuminate the action of TARPs, demonstrate the sensitive balance between positive and negative modulatory action, and provide a mechanistic platform for development of both positive and negative selective AMPAR modulators.

Structure of Transmembrane AMPA Receptor Regulatory Protein Subunit γ2

“…Previously determined structures of TARPs are overall like our structure of TARPγ2 ( Fig. 2b ), and the loop anchor DSB is within structures of TARPγ3 18 and TARPγ8 11,12,19 , and even previously published structures of TARPγ2 6 . However, it is absent, as expected, in the structure of the type-II TARP, TARPγ5 20,21 ( Fig.…”

“…2c ). In contrast, the TARP cleat motif is conserved in all TARPγ3, γ5, and γ8 subunit structures as well as GSG1L 11,18,20 ( Fig. 2d ).…”

Allosteric Competition and Inhibition in AMPA Receptors

“…AMPARs are tightly regulated by TARPs and other auxiliary subunits 23,24,28,32,[54][55][56] and recently identified compounds demonstrate selectivity for particular AMPAR-TARP complexes [57][58][59][60][61][62] .…”

“…However, noncompetitive inhibition of AMPARs may function similarly across different drug types. AMPARs are tightly regulated by TARPs and other auxiliary subunits 23,24,28,32,54–56 and recently identified compounds demonstrate selectivity for particular AMPAR-TARP complexes 57–62 . Structural investigations of the binding sites reveal that drug binding of TARP-dependent inhibitors is at a site distinct from that of PPLMs; the site is within the interface between TARPs and AMPAR transmembrane helices.…”

Allosteric competition and inhibition in AMPA receptors

“…However, noncompetitive inhibition of AMPARs may function similarly across different drug types. AMPARs are tightly regulated by TARPs and other auxiliary subunits 27,28,41,47,55,56 and recently identified compounds (for example, JNJ-55511118, JNJ-118, JNJ-059 and LY-481) demonstrate selectivity for particular AMPAR-TARP complexes 53,[71][72][73][74][75][76] . The binding sites are distinct from those of PPLMs, located within the interface between TARPs and AMPARs.…”