Article | Published:

X-ray structure of a calcium-activated TMEM16 lipid scramblase

Nature volume 516, pages 207212 (11 December 2014) | Download Citation

Abstract

The TMEM16 family of proteins, also known as anoctamins, features a remarkable functional diversity. This family contains the long sought-after Ca2+-activated chloride channels as well as lipid scramblases and cation channels. Here we present the crystal structure of a TMEM16 family member from the fungus Nectria haematococca that operates as a Ca2+-activated lipid scramblase. Each subunit of the homodimeric protein contains ten transmembrane helices and a hydrophilic membrane-traversing cavity that is exposed to the lipid bilayer as a potential site of catalysis. This cavity harbours a conserved Ca2+-binding site located within the hydrophobic core of the membrane. Mutations of residues involved in Ca2+ coordination affect both lipid scrambling in N. haematococca TMEM16 and ion conduction in the Cl channel TMEM16A. The structure reveals the general architecture of the family and its mode of Ca2+ activation. It also provides insight into potential scrambling mechanisms and serves as a framework to unravel the conduction of ions in certain TMEM16 proteins.

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Primary accessions

Data deposits

Coordinates and structure factors have been deposited in the Protein Data Bank under accession codes 4WIS (nhTMEM16 CF1) and 4WIT (nhTMEM16 CF2).

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Acknowledgements

This research was supported by a grant from the European Research Council (no. 339116, AnoBest) and by the Swiss National Science Foundation through the National Centre of Competence in Research TransCure. We thank the staff of the X06SA beamline for support during data collection, B. Blattman and C. Stutz-Ducommun of the Protein Crystallization Center at UZH, for their support with crystallization, B. Dreier for help with MALS experiments, A. Szydelko for providing ecClC as negative control in the scramblase assay and D. Drew for the FGY217 yeast strain. All members of the Dutzler laboratory are acknowledged for help in all stages of the project.

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  1. Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland

    • Janine D. Brunner
    • , Novandy K. Lim
    • , Stephan Schenck
    • , Alessia Duerst
    •  & Raimund Dutzler

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Contributions

J.D.B. screened homologues, purified and crystallized nhTMEM16 and performed scrambling experiments. N.K.L. screened and crystallized homologues, performed electrophysiological recordings and did the MALS measurement. S.S. started the project, made expression vectors and aided in cell culture. A.D. screened homologues. R.D. assisted J.D.B. and N.K.L. during structure determination. J.D.B., N.K.L., S.S. and R.D. jointly planned experiments, analysed data and wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Raimund Dutzler.

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https://doi.org/10.1038/nature13984

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