Cys-Loop Receptor Channel Blockers Also Block GLIC

• Published in: Biophysical journal Vol. 101; no. 12; pp. 2912 - 2918
• Main Authors: Alqazzaz, Mona, Thompson, Andrew J., Price, Kerry L., Breitinger, Hans-Georg, Lummis, Sarah C.R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.12.2011; Biophysical Society; The Biophysical Society
• Subjects: antagonists; Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - chemistry; Bacterial Proteins - physiology; binding sites; Cellular Biophysics and Electrophysiology; Cysteine Loop Ligand-Gated Ion Channel Receptors - antagonists & inhibitors; Cysteine Loop Ligand-Gated Ion Channel Receptors - chemistry; Cysteine Loop Ligand-Gated Ion Channel Receptors - physiology; electrophysiology; Humans; inhibitory concentration 50; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; ion channels; Ions; Ligands; lindane; Lindane - pharmacology; mutagenesis; Pharmacology; Physiology; Picrotoxin - analogs & derivatives; Picrotoxin - pharmacology; Protein Binding; Proteins; receptors; Rimantadine - pharmacology; sequence homology; vertebrates
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2011.10.055

The Gloeobacter ligand-gated ion channel (GLIC) is a bacterial homolog of vertebrate Cys-loop ligand-gated ion channels. Its pore-lining region in particular has a high sequence homology to these related proteins. Here we use electrophysiology to examine a range of compounds that block the channels of Cys-loop receptors to probe their pharmacological similarity with GLIC. The data reveal that a number of these compounds also block GLIC, although the pharmacological profile is distinct from these other proteins. The most potent compound was lindane, a GABAA receptor antagonist, with an IC50 of 0.2 μM. Docking studies indicated two potential binding sites for this ligand in the pore, at the 9′ or between the 0′ and 2′ residues. Similar experiments with picrotoxinin (IC50 = 2.6 μM) and rimantadine (IC50 = 2.6 μM) reveal interactions with 2′Thr residues in the GLIC pore. These locations are strongly supported by mutagenesis data for picrotoxinin and lindane, which are less potent in a T2′S version of GLIC. Overall, our data show that the inhibitory profile of the GLIC pore has considerable overlap with those of Cys-loop receptors, but the GLIC pore has a unique pharmacology.