Cryo-EM structure of the mechanically activated ion channel OSCA1.2
Abstract
Mechanically activated ion channels underlie touch, hearing, shear-stress sensing, and response to turgor pressure. OSCA/TMEM63s are a newly-identified family of eukaryotic mechanically activated ion channels opened by membrane tension. The structural underpinnings of OSCA/TMEM63 function are not explored. Here, we elucidate high resolution cryo-electron microscopy structures of OSCA1.2, revealing a dimeric architecture containing eleven transmembrane helices per subunit and surprising topological similarities to TMEM16 proteins. We locate the ion permeation pathway within each subunit by demonstrating that a conserved acidic residue is a determinant of channel conductance. Molecular dynamics simulations reveal membrane interactions, suggesting the role of lipids in OSCA1.2 gating. These results lay a foundation to decipher how the structural organization of OSCA/TMEM63 is suited for their roles as MA ion channels.
Data availability
Cryo-EM maps of OSCA1.2 in nanodiscs and LMNG have been deposited to the Electron Microscopy Data Bank under accession codes 9112 and 9113. Atomic coordinates of OSCA1.2 in nanodiscs and LMNG have been deposited to the PDB under IDs 6MGV and 6MGW. Due to their large size (300Gb+), the raw data files are available upon request to the corresponding author(s).
-
Cryo-EM map of mechanically activated ion channel OSCA1.2 in nanodiscElectron Microscopy Data Bank, 9112.
-
Cryo-EM map of mechanically activated ion channel OSCA1.2 in LMNGElectron Microscopy Data Bank, 9113.
-
Structure of mechanically activated ion channel OSCA1.2 in nanodiscProtein Data Bank, 6MGV.
-
Structure of mechanically activated ion channel OSCA1.2 in LMNGProtein Data Bank, 6MGW.
Article and author information
Author details
Funding
Howard Hughes Medical Institute
- Ardem Patapoutian
Croucher Foundation
- Che Chun (Alex) Tsui
National Institute of Neurological Disorders and Stroke (1R35NS105067)
- Ardem Patapoutian
Ray Thomas Edwards Foundation
- Andrew B Ward
Wellcome (208361/Z/17/Z)
- Mark SP Sansom
Biotechnology and Biological Sciences Research Council (BB/N000145/1)
- Mark SP Sansom
Biotechnology and Biological Sciences Research Council (BB/R00126X/1)
- Mark SP Sansom
Engineering and Physical Sciences Research Council (EP/R004722/1)
- Mark SP Sansom
Jane Coffin Childs Memorial Fund for Medical Research
- Kei Saotome
Skaggs-Oxford Scholarship
- Che Chun (Alex) Tsui
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Baron Chanda, University of Wisconsin-Madison, United States
Version history
- Received: September 8, 2018
- Accepted: October 11, 2018
- Accepted Manuscript published: November 1, 2018 (version 1)
- Version of Record published: November 14, 2018 (version 2)
Copyright
© 2018, Jojoa Cruz et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
Metrics
-
- 8,068
- views
-
- 1,186
- downloads
-
- 129
- citations
Views, downloads and citations are aggregated across all versions of this paper published by eLife.
Download links
Downloads (link to download the article as PDF)
Open citations (links to open the citations from this article in various online reference manager services)
Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)
Further reading
-
- Evolutionary Biology
- Structural Biology and Molecular Biophysics
Mechanically activated (MA) ion channels convert physical forces into electrical signals, and are essential for eukaryotic physiology. Despite their importance, few bona-fide MA channels have been described in plants and animals. Here, we show that various members of the OSCA and TMEM63 family of proteins from plants, flies, and mammals confer mechanosensitivity to naïve cells. We conclusively demonstrate that OSCA1.2, one of the Arabidopsis thaliana OSCA proteins, is an inherently mechanosensitive, pore-forming ion channel. Our results suggest that OSCA/TMEM63 proteins are the largest family of MA ion channels identified, and are conserved across eukaryotes. Our findings will enable studies to gain deep insight into molecular mechanisms of MA channel gating, and will facilitate a better understanding of mechanosensory processes in vivo across plants and animals.
-
- Structural Biology and Molecular Biophysics
The proteasome controls levels of most cellular proteins, and its activity is regulated under stress, quiescence, and inflammation. However, factors determining the proteasomal degradation rate remain poorly understood. Proteasome substrates are conjugated with small proteins (tags) like ubiquitin and Fat10 to target them to the proteasome. It is unclear if the structural plasticity of proteasome-targeting tags can influence substrate degradation. Fat10 is upregulated during inflammation, and its substrates undergo rapid proteasomal degradation. We report that the degradation rate of Fat10 substrates critically depends on the structural plasticity of Fat10. While the ubiquitin tag is recycled at the proteasome, Fat10 is degraded with the substrate. Our results suggest significantly lower thermodynamic stability and faster mechanical unfolding in Fat10 compared to ubiquitin. Long-range salt bridges are absent in the Fat10 structure, creating a plastic protein with partially unstructured regions suitable for proteasome engagement. Fat10 plasticity destabilizes substrates significantly and creates partially unstructured regions in the substrate to enhance degradation. NMR-relaxation-derived order parameters and temperature dependence of chemical shifts identify the Fat10-induced partially unstructured regions in the substrate, which correlated excellently to Fat10-substrate contacts, suggesting that the tag-substrate collision destabilizes the substrate. These results highlight a strong dependence of proteasomal degradation on the structural plasticity and thermodynamic properties of the proteasome-targeting tags.