Structural basis of Ca2+-dependent activation and lipid transport by a TMEM16 scramblase
- Weill Cornell Medical College, United States
- New York Structural Biology Center, United States
Abstract
The lipid distribution of plasma membranes of eukaryotic cells is asymmetric and phospholipid scramblases disrupt this asymmetry by mediating the rapid, nonselective transport of lipids down their concentration gradients. As a result, phosphatidylserine is exposed to the outer leaflet of membrane, an important step in extracellular signaling networks controlling processes such as apoptosis, blood coagulation, membrane fusion and repair. Several TMEM16 family members have been identified as Ca2+-activated scramblases but the mechanisms underlying their Ca2+-dependent gating and their effects on the surrounding lipid bilayer remain poorly understood. Here we describe three high-resolution cryo-electron microscopy structures of a fungal scramblase from Aspergillus fumigatus, afTMEM16, reconstituted in lipid nanodiscs. These structures reveal that Ca2+-dependent activation of the scramblase entails global rearrangement of the transmembrane and cytosolic domains. These structures, together with functional experiments, suggest that activation of the protein thins the membrane near the transport pathway to facilitate rapid transbilayer lipid movement.
Data availability
CryoEM data have been deposited in the EMPDB database under accession codes: 6E0H, 6DZ7, 6E1O, EMD-8931, EMD-8948, EMD-8959. Raw EM micrographs and un-masked maps are in the process of being deposited.Key parameters of the fluorescence time courses are detailed in the tables and figures and representative traces used in the figures have been provided as source data files. The raw fluorescence time courses are available upon request to the corresponding author.
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afTMEM16 reconstituted in nanodiscs in the presence of Ca2+Protein Data Bank, 6E0H.
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Ca2+-free afTMEM16 in nanodiscElectron Microscopy Data Bank, EMD-8931.
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Ca2+-bound afTMEM16 in nanodiscElectron Microscopy Data Bank, EMD-8948.
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Structure of afTMEM16 in nanodisc in the presence of 0.5 mM Ca2+ and 0.5 mol% Ceramide 24:0Electron Microscopy Data Bank, EMD-8959.
Article and author information
Author details
Funding
National Institute of General Medical Sciences (R01GM106717)
- Alessio Accardi
National Institute of Neurological Disorders and Stroke (R21NS10451)
- Annarita Di Lorenzo
Irma T. Hirschl Trust
- Alessio Accardi
Margaret and Herman Sokol Fellowship
- Maria E Falzone
National Research Foundation of Korea (2013R1A6A3A03064407)
- Byoung-Cheol Lee
Agouron Institute (F00316)
- Edward T Eng
Simons Foundation (349247)
- Edward T Eng
National Institute of General Medical Sciences (GM103310)
- Edward T Eng
National Institute of General Medical Sciences (1R01GM124451-02)
- Crina M Nimigean
Korean Ministry of Science (18-BR-01-02)
- Byoung-Cheol Lee
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2019, Falzone 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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Structural basis of Ca2+-dependent activation and lipid transport by a TMEM16 scramblase
eLife 8:e43229.
https://doi.org/10.7554/eLife.43229
