Glycine Receptor Assays
Background of Glycine Receptor
The glycine receptor chloride channel (GlyR) is a member of the pentameric Cys-loop ion channel receptor family that mediates inhibitory neurotransmission in the spinal cord, brain stem, and retina. They are also found presynaptically, where they modulate neurotransmitter release.
General Structural Features of GlyR
Functional GlyRs assemble as homopentamers of α subunits, or as heteropentamers of α and β subunits. Heteromeric GlyRs comprise either three α and two β or two α and three β subunits. Each transmembrane subunit consists of an extracellular domain containing ligand binding sites, a transmembrane domain consisting of four α-helix domains (TM1-TM4), and a larger intracellular ring domain connecting TM3 and TM4, which affects ionic conductance and mediates interactions with intracellular proteins.
Fig.1 Molecular structure of the human α3 GlyR. (Lynch, 2017)
GlyR in Diseases
Disturbances in glycinergic inhibition at the functional level or impairment in the GlyR life cycle trigger neurological diseases such as startle disease and are associated with pain mechanisms as well as autism spectrum and panic disorders. Another rare neurological disorder associated with disturbed glycinergic inhibition is the GlyR autoantibody-mediated form of stiff-person syndrome (SPS). Startle disease is caused by mutated GlyRs or other proteins expressed at inhibitory synapses. Now GlyRs emerge as a potential therapeutic target for several neurological diseases such as pain, anxiety, drug addiction, and hyperekplexia disease.
Published Data
| Paper Title | Mechanism of gating and partial agonist action in the glycine receptor |
| Journal | Cell |
| Published | 2021 |
| Abstract | Ligand-gated ion channels mediate signal transduction at chemical synapses and transition between resting, open, and desensitized states in response to neurotransmitter binding. The neurotransmitters that produce the highest probability of channel opening (Po) are complete agonists, while those whose production is below the maximum Po are local agonists. The Cys-loop receptor is a class of important neurotransmitter receptors. Here, scientists studied the glycine receptor as a full agonist of glycine and a partial agonist of taurine and G-aminobutyric acid (GABA). Using electrophysiology to show how partial agonists fill the agonist-bound closed channel state and cryo-EM reconstruction to illuminate the intermediate structure, the pre-open state, the research provides previously unseen insight into the conformational state along the receptor response pathway. Further linking agonist-induced conformational changes to Po among members of the receptor family provides a hypothesized mechanism for partial and total agonist action of the Cys-loop receptor. |
| Result |
The scientists isolated full-length GlyR using ethylene maleic acid polymer (SMA) so that the receptor as an endogenous lipid complex can be extracted directly. The full-length receptor was further reorganized into nanodiscs containing brain fat, and then the high-resolution structure of the receptor bound to glycine, taurine, or GABA in the SMA and nanodisc environment was determined. Two strategies, SMA and nanodisk, were explored since they both allow receptors to be coated by protozoan or protozoa-like lipids across the membrane domain, understanding the sensitivity of membrane proteins and the membrane or membrane simulation environment of pentameric ligand-gated channels. These studies of GlyR binding to taurine or GABA revealed the closed state of agonist binding as well as the open and desensitized state, illuminated the conformational state on the receptor response pathway, and provided structure-based insights into some of the mechanisms of agonist action.
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Fig.2 GlyR gating mechanism. (Yu, 2021)
References
- Lynch, J.W.; et al. Glycine receptor drug discovery. Advances in Pharmacology. 2017, 79: 225-253.
- Yu, J.; et al. Mechanism of gating and partial agonist action in the glycine receptor. Cell. 2021, 184(4): 957-968. e21.
