Structure of acid-sensing ion channel 1 at 1.9 Å resolution and low pH

Abstract

Acid-sensing ion channels (ASICs) are voltage-independent, proton-activated receptors that belong to the epithelial sodium channel/degenerin family of ion channels and are implicated in perception of pain, ischaemic stroke, mechanosensation, learning and memory. Here we report the low-pH crystal structure of a chicken ASIC1 deletion mutant at 1.9 Å resolution. Each subunit of the chalice-shaped homotrimer is composed of short amino and carboxy termini, two transmembrane helices, a bound chloride ion and a disulphide-rich, multidomain extracellular region enriched in acidic residues and carboxyl-carboxylate pairs within 3 Å, suggesting that at least one carboxyl group bears a proton. Electrophysiological studies on aspartate-to-asparagine mutants confirm that these carboxyl-carboxylate pairs participate in proton sensing. Between the acidic residues and the transmembrane pore lies a disulphide-rich ‘thumb’ domain poised to couple the binding of protons to the opening of the ion channel, thus demonstrating that proton activation involves long-range conformational changes.

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Figure 1: Function and structure of chicken ASIC1.
Figure 2: Subunit structure and trimer assembly.
Figure 3: Intersubunit interactions and solvent-filled cavities.
Figure 4: Structure and key residues in the transmembrane domains.
Figure 5: Proton- and chloride-binding sites.
Figure 6: Mechanism of pH-dependent gating.

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Acknowledgements

We thank all groups that provided us with ASIC DNAs. We thank T. Kawate for sharing the FSEC screening protocol, Gouaux laboratory members and E. McCleskey for discussions. We also thank the personnel at beamlines 8.2.1 and 8.2.2 of the Advanced Light Source and beamline X29 of the National Synchrotron Light Source. This work was supported by the NIH. E.G. is an investigator with the Howard Hughes Medical Institute.

Author Contributions E.G. and J.J. designed the project. J.J. performed cloning, cell culture, FSEC screening, purification and crystallography work. H.F. and E.B.G. did patch-clamp recordings. E.G. and J.J. wrote the manuscript.

Coordinates have been deposited with the Protein Data Bank under code 2QTS.

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Correspondence to Eric Gouaux.

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Supplementary Information

The file contains Supplementary Table S1, and Supplementary Figures S1-S9 with Legends. (PDF 1209 kb)

Supplementary Movie

This file contains a Supplementary Movie showing speculative mechanism of pH mediated channel gating. Simple animation of domain movement that might occur upon transition from high pH (resting state) to low pH (activated state/desensitized state). At high pH, the finger and thumb domains are separated, perhaps with one or more intervening calcium ions binding in the interdomain cleft and the ion channel is in closed state. Upon exposure to low pH, the calcium ions are released, the key acidic residues bind protons, the thumb and finger domains move closer, pivoting around the β-ball domain, and the ion channel opens and then desensitizes, coupled to the thumb domain by way of the ball-and-socket joint at the wrist junction. This file was uploaded on 11 October 2007 and the legend updated on 18 October 2007. (HTML 1105 kb)

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Jasti, J., Furukawa, H., Gonzales, E. et al. Structure of acid-sensing ion channel 1 at 1.9 Å resolution and low pH. Nature 449, 316–323 (2007). https://doi.org/10.1038/nature06163

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