Glycine receptor mechanism elucidated by electron cryo-microscopy

Abstract

Summary The strychnine-sensitive glycine receptor (GlyR) mediates inhibitory synaptic transmission in the spinal cord and brainstem and is linked to neurological disorders including autism and hyperekplexia. Understanding of molecular mechanisms and pharmacology of GlyRs has been hindered by a dearth of high-resolution structures. Here we report electron cryo-microscopy structures of the α1 GlyR with strychnine, glycine, or glycine/ivermectin. Strychnine arrests the receptor in an antagonist-bound, closed ion channel state, glycine stabilizes the receptor in an agonist-bound open channel state, and the glycine/ivermectin complex adopts a potentially desensitized or partially open state. Relative to the glycine-bound state, strychnine expands the agonist-binding pocket via outward movement of the C loop, promotes rearrangement of the extracellular and transmembrane domain ‘wrist’ interface, and leads to rotation of the transmembrane domain toward the pore axis, occluding the ion conduction pathway. These structures illuminate GlyR mechanism and define a rubric to interpret structures of Cys-loop receptors.

Allosteric binding site in a Cys-loop receptor ligand-binding domain unveiled in the crystal structure of ELIC in complex with chlorpromazine

“…6B) (36). The orthosteric site is also occupied by the competitive antagonist strychnine in the closed α3 GlyR (35) and closed α1 GlyR structures (34). The occupancy of the vestibule site by flurazepam in ELIC was already mentioned in the previous paragraph (firebrick spheres, Fig.…”

“…6C was omitted for clarity because it obscures view on the pore. The ivermectin binding site was also found in the structure of α1 GlyR in complex with ivermectin and glycine (34). Different pore blocker sites have been identified in open GLIC, including at the 13′ position for bromo-lidocaine (brown sphere, Fig.…”

“…Finally, ivermectin in desensitized α1 GlyR occupies the same site as in the open GluCl structure (violet spheres, Fig. 6D) (34). The ivermectin site overlaps with the binding site for the lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in an intermediate GluCl structure (31).…”

“…(33). More recently, the cryo-EM structure of the α1 GlyR was determined in closed, open, and desensitized conformations (34). Finally, the X-ray crystal structure of the α3 GlyR was determined in a strychnine-bound state (35).…”

Crystal structure of a human neuronal nAChR extracellular domain in pentameric assembly: Ligand-bound α2 homopentamer

“…Following this need, structural studies of the nAChR have been the focus of numerous laboratories, leading to the achievement of many breakthroughs, such as the cryo-electron microscopy structure of the Torpedo nAChR (10) and the X-ray crystal structures of acetylcholine binding proteins (AChBPs; homologs of the ECD of nAChR) (11)(12)(13), mouse muscle-type α1 and human neuronal α9 nAChR ECDs (14,15), GLIC and ELIC (two prokaryotic homologs of pLGICs) (16,17), and two α7 nAChR ECD-AChBP chimeras (18,19). In addition, the structures of other members of the superfamily have recently become available, including that of an invertebrate anionic glutamate receptor (20), the human GABA A β3 (21), the mouse 5-HT 3 receptor (22), the human α3 glycine receptor (23), and the zebrafish α1 glycine receptor (24).…”