Structural basis of Ca2+-dependent activation and lipid transport by a TMEM16 scramblase
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.
-
afTMEM16 reconstituted in nanodiscs in the presence of Ca2+Protein Data Bank, 6E0H.
-
Ca2+-free afTMEM16 in nanodiscElectron Microscopy Data Bank, EMD-8931.
-
Ca2+-bound afTMEM16 in nanodiscElectron Microscopy Data Bank, EMD-8948.
-
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.
Reviewing Editor
- László Csanády, Semmelweis University, Hungary
Version history
- Received: October 30, 2018
- Accepted: January 2, 2019
- Accepted Manuscript published: January 16, 2019 (version 1)
- Version of Record published: January 31, 2019 (version 2)
- Version of Record updated: February 1, 2019 (version 3)
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.
Metrics
-
- 5,162
- views
-
- 1,010
- downloads
-
- 89
- 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
-
- Biochemistry and Chemical Biology
- Structural Biology and Molecular Biophysics
The articles in this special issue highlight how modern cellular, biochemical, biophysical and computational techniques are allowing deeper and more detailed studies of allosteric kinase regulation.
-
- Developmental Biology
- Structural Biology and Molecular Biophysics
The receptor tyrosine kinase ROR2 mediates noncanonical WNT5A signaling to orchestrate tissue morphogenetic processes, and dysfunction of the pathway causes Robinow syndrome, brachydactyly B, and metastatic diseases. The domain(s) and mechanisms required for ROR2 function, however, remain unclear. We solved the crystal structure of the extracellular cysteine-rich (CRD) and Kringle (Kr) domains of ROR2 and found that, unlike other CRDs, the ROR2 CRD lacks the signature hydrophobic pocket that binds lipids/lipid-modified proteins, such as WNTs, suggesting a novel mechanism of ligand reception. Functionally, we showed that the ROR2 CRD, but not other domains, is required and minimally sufficient to promote WNT5A signaling, and Robinow mutations in the CRD and the adjacent Kr impair ROR2 secretion and function. Moreover, using function-activating and -perturbing antibodies against the Frizzled (FZ) family of WNT receptors, we demonstrate the involvement of FZ in WNT5A-ROR signaling. Thus, ROR2 acts via its CRD to potentiate the function of a receptor super-complex that includes FZ to transduce WNT5A signals.