Cryo-EM structure of the mechanically activated ion channel OSCA1.2
- The Scripps Research Institute, United States
- University of Oxford, United Kingdom
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).
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Cryo-EM map of mechanically activated ion channel OSCA1.2 in nanodiscElectron Microscopy Data Bank, 9112.
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Cryo-EM map of mechanically activated ion channel OSCA1.2 in LMNGElectron Microscopy Data Bank, 9113.
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Structure of mechanically activated ion channel OSCA1.2 in nanodiscProtein Data Bank, 6MGV.
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Structure of mechanically activated ion channel OSCA1.2 in LMNGProtein Data Bank, 6MGW.
Article and author information
Author details
Sebastian Jojoa Cruz
Che Chun (Alex) Tsui
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.
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.
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Cryo-EM structure of the mechanically activated ion channel OSCA1.2
eLife 7:e41845.
https://doi.org/10.7554/eLife.41845
Further reading
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- 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.
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- Immunology and Inflammation
- Structural Biology and Molecular Biophysics
Antibodies are a major component of adaptive immunity against invading pathogens. Here, we explore possibilities for an analytical approach to characterize the antigen-specific antibody repertoire directly from the secreted proteins in convalescent serum. This approach aims to perform simultaneous antibody sequencing and epitope mapping using a combination of single particle cryo-electron microscopy (cryoEM) and bottom-up proteomics techniques based on mass spectrometry (LC-MS/MS). We evaluate the performance of the deep-learning tool ModelAngelo in determining de novo antibody sequences directly from reconstructed 3D volumes of antibody-antigen complexes. We demonstrate that while map quality is a critical bottleneck, it is possible to sequence antibody variable domains from cryoEM reconstructions with accuracies of up to 80–90%. While the rate of errors exceeds the typical levels of somatic hypermutation, we show that the ModelAngelo-derived sequences can be used to assign the used V-genes. This provides a functional guide to assemble de novo peptides from LC-MS/MS data more accurately and improves the tolerance to a background of polyclonal antibody sequences. Following this proof-of-principle, we discuss the feasibility and future directions of this approach to characterize antigen-specific antibody repertoires.
