Pentameric ligand-gated ion channels (pLGICs) are key players in the early events of electrical signal transduction at chemical synapses. The family codes for a structurally conserved scaffold of channel proteins that open in response to the binding of neurotransmitter molecules. All proteins share a pentameric organization of identical or related subunits that consist of an extracellular ligand-binding domain followed by a transmembrane channel domain. The nicotinic acetylcholine receptor (nAChR) is the most thoroughly studied member of the pLGIC family (for recent reviews see refs 1–3). Two sources of structural information provided an architectural framework for the family. The structure of the soluble acetylcholine-binding protein (AChBP) defined the organization of the extracellular domain and revealed the chemical basis of ligand interaction4,5,6. Electron microscopy studies of the nAChR from Torpedo electric ray have yielded a picture of the full-length protein and have recently led to the interpretation of an electron density map at 4.0 Å resolution7,8,9. Despite the wealth of experimental information, high-resolution structures of any family member have so far not been available. Until recently, the pLGICs were believed to be only expressed in multicellular eukaryotic organisms. The abundance of prokaryotic genome sequences, however, allowed the identification of several homologous proteins in bacterial sources10,11. Here we present the X-ray structure of a prokaryotic pLGIC from the bacterium Erwinia chrysanthemi (ELIC) at 3.3 Å resolution. Our study reveals the first structure of a pLGIC at high resolution and provides an important model system for the investigation of the general mechanisms of ion permeation and gating within the family.
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We thank I. Toth from the Scottish Crop Research Institute for providing g-DNA of E. chrysanthemi, B. Blattmann and A. Haisch for assistance with crystal screening, D. Sargent for help with Xe derivatization, C. Schulze-Briese and the staff of the X06SA beamline for support during data collection, the Protein Analysis Group at the Functional Genomics Center of the University of Zürich for help with mass spectrometry, R. MacKinnon for comments on the manuscript and members of the Dutzler laboratory for help in all stages of the project. Data collection was performed at the Swiss Light Source of the Paul Scherrer Institute. This work was supported by a grant from the National Center for Competence in Research in Structural Biology and the EMBO Young Investigator Program to R.D. R.J.C.H. is affiliated with the Molecular Life Sciences Ph.D. Program of the University/ETH Zürich.
Author Contributions R.D. and R.J.C.H. designed the project. R.J.C.H. performed all experiments. R.D. assisted in data collection, structure determination and electrostatic calculations. R.D. and R.J.C.H. jointly wrote the manuscript.
Coordinates have been deposited in the Protein Data Bank under code 2vl0.
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Hilf, R., Dutzler, R. X-ray structure of a prokaryotic pentameric ligand-gated ion channel. Nature 452, 375–379 (2008). https://doi.org/10.1038/nature06717
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