Exploring the Gating Pathway in an Eukaryotic Ligand-Gated Ion Channel

Abstract

Pentameric ligand-gate ion channels (pLGIC) such as the GABAA-, 5-HT3- and Glycine receptor play a crucial role in neurotransmission and are targeted by a wide variety of drugs including anesthetics, benzodiazepines, and anticonvulsants. Despite their high pharmacological importance, little is known about the pathway from neurotransmitter binding in the extracellular domain to the opening of the channel in the transmembrane domain. Partly, this is due to the lack of high-resolution structural data of pharmacologically relevant receptors. Recently however, the crystallographic structures of the C. elagans glutamate-gated chloride channel (GluCl) both in an apo- as well as in a presumed open state became available (PDB: 4TNV, 4TNW; 3RHW). Based on theses structures along with observations made from molecular dynamics simulations, we focused our interest on one specific loop in the extracellular domain. We have used electrophysiological experiments on Xenopus oocytes to explore the effect of mutations in loop F on the activation of GluCl by glutamate. We also investigated the influence of the partial allosteric agonist ivermectin on glutamate response both in presence and absence of the same mutations in loop F. We found that mutation of a residue in this region has a significant influence on glutamate response. This suggests that this region plays an important role in the pathway between ligand binding to channel opening. These insights should help to better understand the underlying mechanism of this receptor family and might open up new possibilities for drug treatment.