Cais, O. | bioRxiv Science

bioRxiv2022

Modulatory mechanisms of TARP γ8-selective AMPA receptor therapeutics

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 {gamma}8 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-{gamma}8 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.

neuroscience↗

bioRxiv2020

Gating transitions and modulation of a hetero-octameric AMPA glutamate receptor

AMPA glutamate receptors (AMPARs) mediate the majority of excitatory transmission in the brain, and enable synaptic plasticity that underlies learning 1. A diverse array of AMPAR signaling complexes are established by receptor auxiliary subunits, associating in various combinations to modulate trafficking, gating and synaptic strength 2. However, their mechanisms of action are poorly understood. Here, we determine cryo-electron microscopy structures of the heteromeric GluA1/2 receptor assembled with both TARP-{gamma}8 and CNIH2, the predominant AMPAR complex in the forebrain, in both resting and active states (at 3.2 and 3.7 [A], respectively). Consequential for gating regulation, two {gamma}8 and two CNIH2 subunits lodge at distinct sites beneath the ligand-binding domains of the receptor tetramer, with site-specific lipids shaping each interaction. Activation leads to a stark asymmetry between GluA1 and GluA2 along the ion conduction path, and an outward expansion of the channel triggers counter-rotations of both auxiliary subunit pairs, that promotes the active-state conformation. In addition, both {gamma}8 and CNIH2 pivot towards the pore exit on activation, extending their reach for cytoplasmic receptor elements. CNIH2 achieves this through its uniquely extended M2 helix, which has transformed this ER-export factor into a powerful positive AMPAR modulator, capable of providing hippocampal pyramidal neurons with their integrative synaptic properties.

neuroscience↗