Structure and function at the lipid–protein interface of a pentameric ligand-gated ion channel
Pramod Kumar, Gisela D. Cymes, Claudio Grosman
Abstract
Significance The preparation of membrane-protein specimens for structural characterization commonly involves a detergent-solubilization step that is sometimes followed by the reincorporation of the protein into laboratory-made lipid nanodiscs. Whether the native conformation and arrangement of tightly bound lipids are retained despite solubilization or restored upon nanodisc formation cannot be predicted. To determine the structure of the bacterial pentameric ligand-gated ion channel ELIC in its native environment, we overexpressed it in Escherichia coli , fragmented the inner membranes into disc-shaped structures in the absence of detergents, purified discs containing single copies of the protein, and imaged the resulting particles using cryogenic electron microscopy. The obtained three-dimensional reconstruction of the unliganded channel (2.5-Å resolution) revealed previously unseen details of the lipid–protein interface.