Structural Basis for Xenon Inhibition in a Cationic Pentameric Ligand-Gated Ion Channel

Abstract

GLIC receptor is a bacterial pentameric ligand-gated ion channel whose action is inhibited by xenon. Xenon has been used in clinical practice as a potent gaseous anaesthetic for decades, but the molecular mechanism of interactions with its integral membrane receptor targets remains poorly understood. Here we characterize by X-ray crystallography the xenon-binding sites within both the open and “locally-closed” (inactive) conformations of GLIC. Major binding sites of xenon, which differ between the two conformations, were identified in three distinct regions that all belong to the trans-membrane domain of GLIC: 1) in an intra-subunit cavity, 2) at the interface between adjacent subunits, and 3) in the pore. The pore site is unique to the locally-closed form where the binding of xenon effectively seals the channel. A putative mechanism of the inhibition of GLIC by xenon is proposed, which might be extended to other pentameric cationic ligand-gated ion channels.

Allosteric binding site in a Cys-loop receptor ligand-binding domain unveiled in the crystal structure of ELIC in complex with chlorpromazine

“…6B), and the outer-interfacial sites (gray spheres, Fig. 6B) (61). Finally, xenon also occupies the 9′ pore site in locally closed GLIC (gray sphere, Fig.…”

“…6B) (41) or xenon in locally closed GLIC (gray sphere, Fig. 6B) (61). Additional binding sites for xenon in locally closed GLIC are located at the intrasubunit general anesthetic binding site (blue sphere, Fig.…”

“…Finally, xenon also occupies the 9′ pore site in locally closed GLIC (gray sphere, Fig. 6B) (61). Two additional binding sites for bromoform have been localized in the ELIC cocrystal structure, namely at an intersubunit transmembrane site (magenta spheres, Fig.…”

X-Ray Crystallographic Studies for Revealing Binding Sites of General Anesthetics in Pentameric Ligand-Gated Ion Channels

“…Likewise, soaking anesthetics into pLGIC crystals also requires a delicate balance between permeation of sufficient anesthetics into the crystals and potential disruption of the crystal lattice. Non-traditional soaking methods have proved successful for incorporating anesthetics into pLGICs, including adding saturated volatile desflurane to the reservoir well after GLIC crystals are observed (Nury et al, 2011) and pressuring xenon into GLIC crystals in a gas chamber (Sauguet, Fourati, Prange, Delarue, & Colloc’h, 2016). …”

“…Anomalous signals from xenon, bromide or selenium atoms, if they exist in the chosen anesthetics or anesthetic analogs, will also boost the certainty of the assignment of anesthetics. Xenon (Sauguet et al, 2016), 2-bromoethanol (Q. Chen et al, 2017; Sauguet, Howard, et al, 2013), bromoform (Laurent et al, 2016; Spurny et al, 2013), and brominated or seleniated barbiturates (Fourati et al, 2017) have all been successfully identified based on anomalous signals.…”