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Pore architecture and ion sites in acid-sensing ion channels and P2X receptors

Abstract

Acid-sensing ion channels are proton-activated, sodium-selective channels composed of three subunits, and are members of the superfamily of epithelial sodium channels, mechanosensitive and FMRF-amide peptide-gated ion channels. These ubiquitous eukaryotic ion channels have essential roles in biological activities as diverse as sodium homeostasis, taste and pain. Despite their crucial roles in biology and their unusual trimeric subunit stoichiometry, there is little knowledge of the structural and chemical principles underlying their ion channel architecture and ion-binding sites. Here we present the structure of a functional acid-sensing ion channel in a desensitized state at 3 Å resolution, the location and composition of the 8 Å ‘thick’ desensitization gate, and the trigonal antiprism coordination of caesium ions bound in the extracellular vestibule. Comparison of the acid-sensing ion channel structure with the ATP-gated P2X4 receptor reveals similarity in pore architecture and aqueous vestibules, suggesting that there are unanticipated yet common structural and mechanistic principles.

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Figure 1: Identification of a minimally functional chicken ASIC1 construct.
Figure 2: Structure of ASIC1mfc.
Figure 3: Vestibules and possible ion permeation pathways.
Figure 4: Cs + -binding sites.
Figure 5: ASIC and P2X receptors share a common pore architecture.

Accession codes

Primary accessions

Protein Data Bank

Data deposits

Atomic coordinates and structure factors have been deposited with the Protein Data Bank under accession 3HGC.

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Acknowledgements

We thank the personnel at beamlines 5.0.2 of the Advanced Light Source. We also thank C. Canessa for chicken ASIC1 DNA, L. Vaskalis for assistance with illustrations, and Gouaux laboratory members for discussion. This work was supported by a National Institute of General Medical Sciences (NIGMS)-National Research Service Award (NRSA) to E.B.G. and the National Institutes of Health (NIH) (E.G.). E.G. is an investigator with the Howard Hughes Medical Institute.

Author Contributions E.G. and E.B.G. designed the project. E.B.G. performed cloning, cell culture, FSEC screening, purification, crystallography and electrophysiology. T.K. provided the zebrafish ΔP2X4 crystal structure. E.B.G. and E.G. wrote the manuscript.

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Correspondence to Eric Gouaux.

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Gonzales, E., Kawate, T. & Gouaux, E. Pore architecture and ion sites in acid-sensing ion channels and P2X receptors. Nature 460, 599–604 (2009). https://doi.org/10.1038/nature08218

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