27 research outputs found
Cys-Loop Receptor Channel Blockers Also Block GLIC
AbstractThe 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
Varenicline Interactions at the 5‑HT<sub>3</sub> Receptor Ligand Binding Site are Revealed by 5‑HTBP
Cys-loop receptors are the site of
action of many therapeutic drugs.
One of these is the smoking cessation agent varenicline, which has
its major therapeutic effects at nicotinic acetylcholine (nACh) receptors
but also acts at 5-HT<sub>3</sub> receptors. Here, we report the X-ray
crystal structure of the 5-HT binding protein (5-HTBP) in complex
with varenicline, and test the predicted interactions by probing the
potency of varenicline in a range of mutant 5-HT<sub>3</sub> receptors
expressed in HEK293 cells and <i>Xenopus</i> oocytes. The
structure reveals a range of interactions between varenicline and
5-HTBP. We identified residues within 5 Ã… of varenicline and
substituted the equivalent residues in the 5-HT<sub>3</sub> receptor
with Ala or a residue with similar chemical properties. Functional
characterization of these mutant 5-HT<sub>3</sub> receptors, using
a fluorescent membrane potential dye in HEK cells and voltage clamp
in oocytes, supports interactions between varenicline and the receptor
that are similar to those in 5-HTBP. The structure also revealed C-loop
closure that was less than in the 5-HT-bound 5-HTBP, and hydrogen
bonding between varenicline and the complementary face of the binding
pocket via a water molecule, which are characteristics consistent
with partial agonist behavior of varenicline in the 5-HT<sub>3</sub> receptor. Together, these data reveal detailed insights into the
molecular interaction of varenicline in the 5-HT<sub>3</sub> receptor