Journal of Biological Chemistry
Volume 286, Issue 51, 23 December 2011, Pages 43913-43924
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Neurobiology
Molecular Determinants of Ivermectin Sensitivity at the Glycine Receptor Chloride Channel*

https://doi.org/10.1074/jbc.M111.262634Get rights and content
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Ivermectin is an anthelmintic drug that works by activating glutamate-gated chloride channel receptors (GluClRs) in nematode parasites. GluClRs belong to the Cys-loop receptor family that also includes glycine receptor (GlyR) chloride channels. GluClRs and A288G mutant GlyRs are both activated by low nanomolar ivermectin concentrations. The crystal structure of the Caenorhabditis elegans α GluClR complexed with ivermectin has recently been published. Here, we probed ivermectin sensitivity determinants on the α1 GlyR using site-directed mutagenesis and electrophysiology. Based on a mutagenesis screen of transmembrane residues, we identified Ala288 and Pro230 as crucial sensitivity determinants. A comparison of the actions of selamectin and ivermectin suggested the benzofuran C05-OH was required for high efficacy. When taken together with docking simulations, these results supported a GlyR ivermectin binding orientation similar to that seen in the GluClR crystal structure. However, whereas the crystal structure shows that ivermectin interacts with the α GluClR via H-bonds with Leu218, Ser260, and Thr285 (α GluClR numbering), our data indicate that H-bonds with residues homologous to Ser260 and Thr285 are not important for high ivermectin sensitivity or direct agonist efficacy in A288G α1 GlyRs or three other GluClRs. Our data also suggest that van der Waals interactions between the ivermectin disaccharide and GlyR M2–M3 loop residues are unimportant for high ivermectin sensitivity. Thus, although our results corroborate the ivermectin binding orientation as revealed by the crystal structure, they demonstrate that some of the binding interactions revealed by this structure do not pertain to other highly ivermectin-sensitive Cys-loop receptors.

Chloride Channels
Drug Action
Membrane Biophysics
Neurotransmitter Receptors
Parasitology
Cys-loop Receptor
Binding Site
Electrophysiology
Molecular Docking
Site-directed Mutagenesis

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*

This work was supported in part by the Australian Research Council and the National Health and Medical Research Council of Australia.

1

Supported by Australian postgraduate awards.

2

Present address: Dept. of Molecular and Cellular Neurophysiology, Technical University of Darmstadt, 64287 Darmstadt, Germany.

3

Present address: Ion Channel Biotechnology Centre, Dundalk Institute of Technology, Dundalk, Ireland.