Cation-selective mutations in the M2 domain of the inhibitory glycine receptor channel reveal determinants of ion-charge selectivity

Keramidas, Angelo, Moorhouse, Andrew J., Pierce, Kerrie D. and Schofield, Peter R. (2002) Cation-selective mutations in the M2 domain of the inhibitory glycine receptor channel reveal determinants of ion-charge selectivity. Journal of General Physiology, 119 5: 393-410. doi:10.1085/jgp.20028552


Author Keramidas, Angelo
Moorhouse, Andrew J.
Pierce, Kerrie D.
Schofield, Peter R.
Title Cation-selective mutations in the M2 domain of the inhibitory glycine receptor channel reveal determinants of ion-charge selectivity
Journal name Journal of General Physiology   Check publisher's open access policy
ISSN 0022-1295
1540-7748
Publication date 2002-05
Year available 2002
Sub-type Article (original research)
DOI 10.1085/jgp.20028552
Open Access Status Not Open Access
Volume 119
Issue 5
Start page 393
End page 410
Total pages 18
Place of publication New York, NY, United States
Publisher Rockefeller University Press
Language eng
Formatted abstract
Ligand-gated ion channel receptors mediate neuronal inhibition or excitation depending on their ion charge selectivity. An investigation into the determinants of ion charge selectivity of the anion-selective α1 homomeric glycine receptor (α1 glycine receptor [GlyR]) was undertaken using point mutations to residues lining the extra- and intracellular ends of the ion channel. Five mutant GlyRs were studied. A single substitution at the intracellular mouth of the channel (A-1′E GlyR) was sufficient to convert the channels to select cations over anions with PCl/PNa = 0.34. This result delimits the selectivity filter and provides evidence that electrostatic interactions between permeating ions and pore residues are a critical factor in ion charge selectivity. The P-2′Δ mutant GlyR retained its anion selectivity (PCl/PNa = 3.81), but it was much reduced compared with the wild-type (WT) GlyR (PCl/PNa = 27.9). When the A-1′E and the P-2′Δ mutations were combined (selectivity double mutant [SDM] GlyR), the relative cation permeability was enhanced (PCl/PNa = 0.13). The SDM GlyR was also Ca2+ permeable (PCa/PNa = 0.29). Neutralizing the extracellular mouth of the SDM GlyR ion channel (SDM+R19′A GlyR) produced a more Ca2+-permeable channel (PCa/PNa = 0.73), without drastically altering monovalent charge selectivity (PCl/PNa = 0.23). The SDM+R19′E GlyR, which introduces a negatively charged ring at the extracellular mouth of the channel, further enhanced Ca2+ permeability (PCa/PNa = 0.92), with little effect on monovalent selectivity (PCl/PNa = 0.19). Estimates of the minimum pore diameter of the A-1′E, SDM, SDM+R19′A, and SDM+R19′E GlyRs revealed that these pores are larger than the α1 GlyR, with the SDM-based GlyRs being comparable in diameter to the cation-selective nicotinic acetylcholine receptors. This result provides evidence that the diameter of the ion channel is also an important factor in ion charge selectivity.
Keyword Ligand-gated ion channels
Electrostatics
Pore diameter
Permeability
Selectivity filter
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: Queensland Brain Institute Publications
 
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Created: Tue, 02 Aug 2016, 15:35:05 EST by Angelo Keramidas on behalf of Queensland Brain Institute