
Stepwise activation mechanism of the scramblase nhTMEM16 revealed by cryo-EM
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Abstract
Scramblases catalyze the movement of lipids between both leaflets of a bilayer. Whereas the X-ray structure of the protein nhTMEM16 has previously revealed the architecture of a Ca2+-dependent lipid scramblase, its regulation mechanism has remained elusive. Here, we have used cryo-electron microscopy and functional assays to address this question. Ca2+-bound and Ca2+-free conformations of nhTMEM16 in detergent and lipid nanodiscs illustrate the interactions with its environment and they reveal the conformational changes underlying its activation. In this process, Ca2+-binding induces a stepwise transition of the catalytic subunit cavity, converting a closed cavity that is shielded from the membrane in the absence of ligand, into a polar furrow that becomes accessible to lipid headgroups in the Ca2+-bound state. Additionally, our structures demonstrate how nhTMEM16 distorts the membrane at both entrances of the subunit cavity, thereby decreasing the energy barrier for lipid movement.
Article and author information
Author details
Funding
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (740.018.016)
- Cristina Paulino
H2020 European Research Council (339116)
- Raimund Dutzler
H2020 European Research Council (AnoBest)
- Raimund Dutzler
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Kenton Jon Swartz, National Institute of Neurological Disorders and Stroke, National Institutes of Health, United States
Publication history
- Received: December 12, 2018
- Accepted: February 8, 2019
- Accepted Manuscript published: February 20, 2019 (version 1)
- Accepted Manuscript updated: February 21, 2019 (version 2)
- Version of Record published: March 12, 2019 (version 3)
Copyright
© 2019, Kalienkova 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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Further reading
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- Biochemistry and Chemical Biology
- Structural Biology and Molecular Biophysics
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- Biochemistry and Chemical Biology
- Structural Biology and Molecular Biophysics