Identification of an inhibitory Zn2+ binding site on the human glycine receptor alpha1 subunit

Harvey, R.J., Thomas, P., James, C.H., Wilderspin, A.F. and Smart, T.G. (1999) Identification of an inhibitory Zn2+ binding site on the human glycine receptor alpha1 subunit. Journal of Physiology, 520 (1). pp. 53-64. 10.1111/j.1469-7793.1999.00053.x.

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DOI: 10.1111/j.1469-7793.1999.00053.x

Abstract

Whole-cell glycine-activated currents were recorded from human embryonic kidney (HEK) cells expressing wild-type and mutant recombinant homomeric glycine receptors (GlyRs) to locate the inhibitory binding site for Zn2+ ions on the human α1 subunit. 2.Glycine-activated currents were potentiated by low concentrations of Zn2+ (<10 μm) and inhibited by higher concentrations (>100 μm) on wild-type α1 subunit GlyRs. 3.Lowering the external pH from 7.4 to 5.4 inhibited the glycine responses in a competitive manner. The inhibition caused by Zn2+ was abolished leaving an overt potentiating effect at 10 μm Zn2+ that was exacerbated at 100 μm Zn2+. 4.The identification of residues involved in the formation of the inhibitory binding site was also assessed using diethylpyrocarbonate (DEPC), which modifies histidines. DEPC (1 mm) abolished Zn2+-induced inhibition and also the potentiation of glycine-activated currents by Zn2+. 5.The reduction in glycine-induced whole-cell currents in the presence of high (100 μm) concentrations of Zn2+ did not increase the rate of glycine receptor desensitisation. 6.Systematic mutation of extracellular histidine residues in the GlyR α1 subunit revealed that mutations H107A or H109A completely abolished inhibition of glycine-gated currents by Zn2+. However, mutation of other external histidines, H210, H215 and H419, failed to prevent inhibition by Zn2+ of glycine-gated currents. Thus, H107 and H109 in the extracellular domain of the human GlyR α1 subunit are major determinants of the inhibitory Zn2+ binding site. 7.An examination of Zn2+ co-ordination in metalloenzymes revealed that the histidine- hydrophobic residue-histidine motif found to be responsible for binding Zn2+ in the human GlyR α1 subunit is also shared by some of these enzymes. Further comparison of the structure and location of this motif with a generic model of the GlyR α1 subunit suggests that H107 and H109 participate in the formation of the inhibitory Zn2+ binding site at the apex of a β sheet in the N-terminal extracellular domain.

Item Type:Article
Departments, units and centres:Department of Pharmacology > Department of Pharmacology
ID Code:2004
Journal or Publication Title:Journal of Physiology
Deposited By:Library Staff
Deposited On:01 Apr 2011 14:29
Last Modified:16 Jun 2011 09:50

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