Cryo-EM Studies of TMEM16F Calcium-Activated Ion Channel Suggest Features Important for Lipid Scrambling

Shengjie Feng; Shangyu Dang; Tina Wei Han; Wenlei Ye; Peng Jin; Tong Cheng; Junrui Li; Yuh Nung Jan; Lily Yeh Jan; Yifan Cheng

doi:10.1016/j.celrep.2019.06.023

Cryo-EM Studies of TMEM16F Calcium-Activated Ion Channel Suggest Features Important for Lipid Scrambling

Cell Rep. 2019 Jul 9;28(2):567-579.e4. doi: 10.1016/j.celrep.2019.06.023.

Authors

Shengjie Feng¹, Shangyu Dang², Tina Wei Han¹, Wenlei Ye¹, Peng Jin¹, Tong Cheng¹, Junrui Li², Yuh Nung Jan³, Lily Yeh Jan⁴, Yifan Cheng⁵

Affiliations

¹ Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA.
² Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
³ Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA; Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA.
⁴ Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA; Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA. Electronic address: lily.jan@ucsf.edu.
⁵ Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA; Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA. Electronic address: ycheng@ucsf.edu.

Abstract

As a Ca²⁺-activated lipid scramblase and ion channel that mediates Ca²⁺ influx, TMEM16F relies on both functions to facilitate extracellular vesicle generation, blood coagulation, and bone formation. How a bona fide ion channel scrambles lipids remains elusive. Our structural analyses revealed the coexistence of an intact channel pore and PIP₂-dependent protein conformation changes leading to membrane distortion. Correlated to the extent of membrane distortion, many tightly bound lipids are slanted. Structure-based mutagenesis studies further reveal that neutralization of some lipid-binding residues or those near membrane distortion specifically alters the onset of lipid scrambling, but not Ca²⁺ influx, thus identifying features outside of channel pore that are important for lipid scrambling. Together, our studies demonstrate that membrane distortion does not require open hydrophilic grooves facing the membrane interior and provide further evidence to suggest separate pathways for lipid scrambling and ion permeation.

Keywords: PIP(2) modulation; TMEM16F; calcium; cryo-EM; ion channel; lipid scramblase; membrane distortion.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Abstract

Publication types

Grants and funding