Out-of-the-groove transport of lipids by TMEM16 and GPCR scramblases.

TitleOut-of-the-groove transport of lipids by TMEM16 and GPCR scramblases.
Publication TypeJournal Article
Year of Publication2018
AuthorsMalvezzi M, Andra KK, Pandey K, Lee B-C, Falzone ME, Brown A, Iqbal R, Menon AK, Accardi A
JournalProc Natl Acad Sci U S A
Date Published2018 07 24
KeywordsAnoctamins, Biological Transport, Active, HEK293 Cells, Humans, Lipid Metabolism, Phospholipid Transfer Proteins, Receptors, G-Protein-Coupled, Saccharomyces cerevisiae

Phospholipid scramblases externalize phosphatidylserine to facilitate numerous physiological processes. Several members of the structurally unrelated TMEM16 and G protein-coupled receptor (GPCR) protein families mediate phospholipid scrambling. The structure of a TMEM16 scramblase shows a membrane-exposed hydrophilic cavity, suggesting that scrambling occurs via the ‟credit-card" mechanism where lipid headgroups permeate through the cavity while their tails remain associated with the membrane core. Here we show that afTMEM16 and opsin, representatives of the TMEM16 and GCPR scramblase families, transport phospholipids with polyethylene glycol headgroups whose globular dimensions are much larger than the width of the cavity. This suggests that transport of these large headgroups occurs outside rather than within the cavity. These large lipids are scrambled at rates comparable to those of normal phospholipids and their presence in the reconstituted vesicles promotes scrambling of normal phospholipids. This suggests that both large and small phospholipids can move outside the cavity. We propose that the conformational rearrangements underlying TMEM16- and GPCR-mediated credit-card scrambling locally deform the membrane to allow transbilayer lipid translocation outside the cavity and that both mechanisms underlie transport of normal phospholipids.

Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID29925604
PubMed Central IDPMC6065010
Grant ListP41 GM103310 / GM / NIGMS NIH HHS / United States
R21 EY028314 / EY / NEI NIH HHS / United States
T32 GM008539 / GM / NIGMS NIH HHS / United States
R01 GM106717 / GM / NIGMS NIH HHS / United States
S10 OD019994 / OD / NIH HHS / United States