Dynamic closed states of a ligand-gated ion channel captured by cryo-EM and simulations

Ligand-gated ion channels are critical mediators of electrochemical signal transduction across evolution. Biophysical and pharmacological characterization of these receptor proteins relies on high-quality structures in multiple, subtly distinct functional states. However, structural data in this family remain limited, particularly for resting and intermediate states on the activation pathway.

Here, we report cryo-electron microscopy (cryo-EM) structures of the proton-activated Gloeobacter violaceus ligand-gated ion channel (GLIC) under three pH conditions. Decreased pH was associated with improved resolution and side chain rearrangements at the subunit/domain interface, particularly involving functionally important residues in the β1–β2 and M2–M3 loops.

Molecular dynamics simulations substantiated flexibility in the closed-channel extracellular domains relative to the transmembrane ones and supported electrostatic remodeling around E35 and E243 in proton-induced gating. Exploration of secondary cryo-EM classes further indicated a low-pH population with an expanded pore.

These results allow us to define distinct protonation and activation steps in pH-stimulated conformational cycling in GLIC, including interfacial rearrangements largely conserved in the pentameric channel family.

Citation

Urška Rovšnik, Yuxuan Zhuang, Björn O Forsberg, Marta Carroni, Linnea Yvonnesdotter, Rebecca J Howard, Erik Lindahl (2021):
Dynamic closed states of a ligand-gated ion channel captured by cryo-EM and simulations.
Life Science Alliance 4(8)
https://doi.org/10.26508/lsa.202101011