Crystal Structures of Potent Dimeric Positive Allosteric Modulators at the Ligand-Binding Domain of the GluA2 Receptor

Abstract

The ionotropic glutamate receptor GluA2 is considered to be an attractive target for positive allosteric modulation for the development of pharmacological tools or cognitive enhancers. Here, we report a detailed structural characterization of two recently reported dimeric positive allosteric modulators, TDPAM01 and TDPAM02, with nanomolar potency at GluA2. Using X-ray crystallography, TDPAM01 and TDPAM02 were crystallized in the ligandbinding domain of the GluA2 flop isoform as well as in the flip-like mutant N775S and the preformed dimer L504Y-N775S. In all structures, one modulator molecule binds at the dimer interface with two characteristic hydrogen bonds being formed from the modulator to Pro515. Whereas the GluA2 dimers and modulator binding mode are similar when crystallized in the presence of L-glutamate, the shape of the binding site differs when no L-glutamate is present. TDPAM02 has no effect on domain closure in both apo and L-glutamate bound GluA2 dimers compared to structures without modulator.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

“…Glutamate Receptor Ion Channels revealed that different PAMs can have distinct binding modes at different subsites within the ABD dimer interface (Sun et al, 2002;Jin et al, 2005;Kaae et al, 2007;Hald et al, 2009;Ptak et al, 2009;Sobolevsky et al, 2009;Timm et al, 2011;Krintel et al, 2013;Norholm et al, 2013;Goffin et al, 2018;Laulumaa et al, 2018). This discovery has stimulated development of newer classes of modulators with improved potency (Kaae et al, 2007;Pohlsgaard et al, 2011;Ptak et al, 2014;Laulumaa et al, 2018) (Section IX. Exogenous Positive and Negative Allosteric Modulators).…”

“…For other PAMs, such as aniracetam and CX614, one molecule binds but with two overlapping conformations in a more central site within the dimer interface (Jin et al, 2005;Krintel et al, 2013;Goffin et al, 2018). Finally, the PAM N,N 0 -(1,4-Phenylenedi-2,1-ethanediyl)bis-2-propanesulfonamide (CMPDA) has a symmetrical chemical structure and binds to a central site (Kaae et al, 2007;Sobolevsky et al, 2009;Timm et al, 2011;Laulumaa et al, 2018). The AMPA receptor PAMs increase the stability of the ABD dimer interface to slow the transition into the desensitized state, and a subset of PAMs also slows receptor deactivation (Jin et al, 2005;Mitchell and Fleck, 2007;Partin, 2015;Shaffer et al, 2015).…”

“…The discovery of the distinct binding modes of AMPA receptor PAMs, with subsites spanning the dimer interface (Fig. 41), stimulated the development of dimeric PAMs that interact with multiple subsites with increased affinity (Kaae et al, 2007;Ptak et al, 2014;Laulumaa et al, 2018). Characterization of early AMPA receptor PAMs has been described in several excellent reviews (Partin, 2015;Brogi et al, 2019).…”

Development of Thiochroman Dioxide Analogues of Benzothiadiazine Dioxides as New Positive Allosteric Modulators of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors

“…These compounds are active in vitro as AMPAR PAMs with nanomolar potency at GluA2, and they were also found to interact on both sites of the GluA2-LBD dimer interface. 13,14 In the present paper, we disclose the results of our studies on a new series of AMPAR PAMs designed using the classical isosteric replacement concept. 15,16 We have here focused our efforts on the replacement of the two nitrogen atoms of the thiadiazine ring by carbon atoms, leading to the preparation of thiochroman 1,1-dioxides.…”

“…Finally, a structure-based approach led to the preparation of dimers 6 and 7 . These compounds are active in vitro as AMPAR PAMs with nanomolar potency at GluA2, and they were also found to interact on both sites of the GluA2-LBD dimer interface. , …”