1.A.10.1.1
AMPA-selective glutamate ionotropic channel receptor (GIC; AMPAR), kainate-subtype, GluR-K1; GluR1; GluR-A; GluA1; Gria1 of 906 aas (preferentially monovalent cation selective). A mature complex contains GluR1, TARPs, and PSD-95 (Fukata et al. 2005). The receptor contributes to amygdala-dependent emotional learning and fear conditioning (Humeau et al., 2007). Transmembrane AMPAR regulatory protein (TARP) gamma-7 (TC#8.A.16.2.5) selectively enhances the synaptic expression of Ca²⁺-permeable (CP-AMPARs) and suppresses calcium-impermeable (CI-AMPAR) activities (Studniarczyk et al. 2013).  Thus, TARPs modulate the pharmacology and gating of AMPA-type glutamate receptors (Soto et al. 2014).  TARPs interact with the N-terminal domain of the AMPAR and control channel gating; residues in the receptor and the TARP involved in this interaction have been identified (Cais et al. 2014).  The auxilary protein, Shisa9 or CKAMP44 (UniProt acc# B4DS77), has a C-terminal PDZ domain that allows interaction with scaffolding proteins and AMPA glutamate receptors (Karataeva et al. 2014).  The transmembrane domain alone can tetramerize (Gan et al. 2016). The most potent and well-tolerated AMPA receptor inhibitors, used to treat epilepsy, act via a noncompetitive mechanism.  The crystal structures of the rat AMPA-subtype GluA2 receptor in complex with three noncompetitive inhibitors have been solved. The inhibitors bind to a binding site, completely conserved between rat and human, at the interface between the ion channel and linkers connecting it to the ligand-binding domains (Yelshanskaya et al. 2016). The endogenous neuropeptide, cyclopropylglycine, at a physiological concentration of 1 μM, enhances the transmembrane AMPA currents in rat cerebellar Purkinje cells (Gudasheva et al. 2016). The energetics of glutamate binding have been estimated (Yu and Lau 2017). The TMEM108 protein (Q6UXF1 of 575 aas and 2 TMSs, N- and C-terminal, is required for surface expression of AMPA receptors (Jiao et al. 2017). CERC-611 is a selective antagonist of AMPA receptors containing transmembrane AMPA receptor regulatory protein (TARP; TC# 8.A.16) gamma-8 (Witkin et al. 2017). Drug effects, regulatory protein modulators and positive allosteric modulators have been reviewed (Fu et al. 2019). Herguedas et al. 2019 presented a cryo-EM structure of the heteromeric GluA1/2 receptor associated with two transmembrane AMPAR regulatory protein (TARP) gamma8 auxiliary subunits, the principal AMPAR complex at hippocampal synapses.  The native heterotetrameric AMPA-R adopts various conformations, which reflect a variable separation of the two dimeric extracellular amino-terminal domains; members of the stargazin/TARP family of transmembrane proteins co-purify with AMPA-Rs and contribute to the density representing the transmembrane region of the complex. Glutamate and cyclothiazide altered the conformational equilibrium of the channel complex, suggesting that desensitization is related to separation of the N-terminal domains (Nakagawa et al. 2005). Positive allosteric modulators (PAMs) of AMPA receptors boost cognitive performance in clinical studies, and mibampator and BIIB104 discriminate between AMPARs complexed with distinct TARPs, and particularly those with lower stargazin/gamma2 efficacy such as BIIB104 (Ishii et al. 2020). Yelshanskaya et al. 2020 identified trans-4-butylcyclohexane carboxylic acid (4-BCCA) binding sites in the transmembrane domain of AMPA receptors, at the lateral portals formed by TMSs M1-M4. At this binding site, 4-BCCA is very dynamic, assumes multiple poses and can enter the ion channel pore. Cannabidiol inhibits febrile seizure by modulating AMPA receptor kinetics through its interaction with the N-terminal domain of GluA1/GluA2 (Yu et al. 2020). Inhibition of AMPA receptors (AMPARs, e.g., TC# 1.A.10.1.1) containing transmembrane AMPAR regulatory protein gamma-8 (TC# 8.A.61.1.10) with JNJ-55511118 (TC#8.A.179.1.1) shows preclinical efficacy in reducing chronic repetitive alcohol self-administration (Hoffman et al. 2021). Mechanisms underlying TARP modulation of the GluA1/2-gamma8 AMPA receptor have been studied (Herguedas et al. 2022). L-Glutamate is the main excitatory neurotransmitter in the central nervous system (CNS). Its associated receptors, localized on neuronal and non-neuronal cells, mediate rapid excitatory synaptic transmission in the CNS and regulate a wide range of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors selective to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) also play an important role in numerous neurological disorders.  Golubeva et al. 2022 examined the structural diversity of chemotypes of agonists, competitive AMPA receptor antagonists, positive and negative allosteric modulators, TARP-dependent allosteric modulators, ion channel blockers ans their binding sites.