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Stepwise activation mechanism of the scramblase nhTMEM16 revealed by cryo-EM.


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.

SUBMITTER: Kalienkova V 

PROVIDER: S-EPMC6414200 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Stepwise activation mechanism of the scramblase nhTMEM16 revealed by cryo-EM.

Kalienkova Valeria V   Clerico Mosina Vanessa V   Bryner Laura L   Oostergetel Gert T GT   Dutzler Raimund R   Paulino Cristina C  

eLife 20190221


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 Ca<sup>2+</sup>-dependent lipid scramblase, its regulation mechanism has remained elusive. Here, we have used cryo-electron microscopy and functional assays to address this question. Ca<sup>2+</sup>-bound and Ca<sup>2+</sup>-free conformations of nhTMEM16 in detergent and lipid nanodiscs illustrate the interactions with  ...[more]

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