Replies to post #1548 on RespireRx Pharmaceuticals Inc (RSPI)

[gfp927z]

An SFN paper from Organon studying the high impact site. This site was identified several years ago, and is where high impacts AMPA upmodulators bind (CX-546, CX-614, cyclothiazide, Lilly's compounds, etc, and aniracetam also binds here). Dr. Rogers discussed related research at the annual SHM several years ago -

>>> Program#/Poster#: 231.5/D2
Title: Biostructural studies of the AMPA GluR1flip and GluR2flip receptor complexes
Location: Georgia World Congress Center: Halls B3-B5
Presentation Start/End Time: Sunday, Oct 15, 2006, 1:00 PM - 2:00 PM
Authors: *J. A. MORROW1, B. KAZEMIER2, S. M. BASTEN2, J. K. MACLEAN3;
1Molecular Pharmacology, Organon Laboratories Limited, Newhouse, UNITED KINGDOM, 2Molecular Pharmacology, NV Organon, Oss, THE NETHERLANDS, 3Medicinal Chemistry, Organon Laboratories Limited, Newhouse, UNITED KINGDOM.

AMPA receptors are ligand-gated ion channels that mediate fast excitatory amino acid transmission in the CNS and participate in forms of synaptic plasticity underlying learning and memory. Drugs that positively modulate the AMPA receptor hold promise for the treatment of cognition related disorders such as Alzheimer’s disease and schizophrenia. The receptor is a heterotetrameric complex formed from subunits encoded by four genes GluR1-4 each of which exists in alternative splice variants termed flip and flop. The receptor subunit and splice variant composition confer unique functional and pharmacological properties on the receptor. Structural studies performed using the GluR2 flop subunit has identified a binding pocket for AMPA receptor positive modulators, thereby advancing our understanding of the biophysical effects elicited by different classes of modulators. We have performed biostructrural studies on the GluR2flip and GluR1flip subunits and compared this with the published GluR2flop structure. The GluR2flip and GluR2flop S1S2 ligand binding domain (LBD) constructs differ by only four amino acids. High resolution crystal structures demonstrate the GluR2 flip LBD structure is essentially identical to that of the published for GluR2flop. Furthermore, cyclothiazide binds GluR2 flip in a manner identical to that predicted by the GluR2flip N754S mutant. Co-crystallisation studies with the ampakine CX546 in the GluR2 flip construct reveal that a single molecule of CX546 occupies a binding site a the hinge region of the LBD ‘clamshell’ similar to that observed with aniracetam and CX614. The interactions between CX546 and the binding pocket are predominantly hydrophobic in nature. High resolution crystal structure studies with the GluR1flip reveal subtle differences in comparison to GluR2flip. While the allosteric modulator binding pockets are quite similar, any differences are propagated at changes in the agonist binding site with the ‘clamshell’ being slightly more closed in the GluR1-glutamate bound complex in comparison with the GluR2-glutamate complex. A greater understanding of the structural differences between AMPA receptor subunits should lead to rational structure base drug design of subtype selective AMPA receptor modulators with enormous clinical potential. <<<