Abstract
Both lipid and ion translocation by Ca2+-regulated TMEM16 transmembrane proteins utilizes a membrane-exposed hydrophilic groove. Several conformations of the groove are observed in TMEM16 protein structures, but how these conformations form, and what functions they support, remains unknown. From analyses of atomistic molecular dynamics simulations of Ca2+-bound nhTMEM16 we find that the mechanism of a conformational transition of the groove from membrane-exposed to occluded from the membrane involves the repositioning of transmembrane helix 4 (TM4) following its disengagement from a TM3/TM4 interaction interface. Residue L302 is a key element in the hydrophobic TM3/TM4 interaction patch that braces the open-groove conformation, which should be changed by an L302A mutation. The structure of the L302A mutant determined by cryogenic electron microscopy (cryo-EM) reveals a partially closed groove that could translocate ions, but not lipids. This is corroborated with functional assays showing severely impaired lipid scrambling, but robust channel activity by L302A.
Highlights
Both lipid and ion translocation by Ca2+-regulated TMEM16 transmembrane proteins utilizes a membrane-exposed hydrophilic groove
We recently reported on rare scrambling-incompetent conformational states observed in our molecular dynamics (MD) simulations of the Ca2+bound nhTMEM1621 in which the groove is structurally similar to the Ca2+-bound intermediate conformations of TMEM16 scramblases and channels[9,10,17,19]
Our results illuminate the detailed molecular mechanism by which the lipid groove of the nhTMEM16 scramblase can rearrange from a membrane-exposed conformation to an intermediate state that is occluded from the membrane, forming an ion-conductive conformation
Summary
Both lipid and ion translocation by Ca2+-regulated TMEM16 transmembrane proteins utilizes a membrane-exposed hydrophilic groove. The Ca2+ binding sites of the TMEM16 scramblases are disrupted by repositioning of the intracellular half of TM69,10,17–19, the extracellular portion of TM4 bends and interacts with TM6, occluding the groove from the membrane (except in nhTMEM16 in detergent[18]) In this conformation, termed here Ca2+-free closed, the internal groove diameter of
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
