Phospholipid Flip Mediated by Model Flippases

Abstract

Lipid translocation from one lipid bilayer leaflet to the other, termed flip-flop, is required for the distribution of newly synthesized phospholipids during membrane biogenesis over both membrane leaflets. However, a dedicated biogenic lipid flippase has not yet been identified and the mechanism by which phospholipids are translocated across the bilayer is unclear. Here, we present the flippase activity of de novo designed transmembrane helix peptides. The efficiency by which these peptides facilitate flip of reporter lipids critically depends on their helix backbone dynamics, the charge state of polar flanking residues, and the composition of the host membrane. In particular, increased backbone dynamics of the transmembrane helix relates to its increased ability to flip lipids with phosphatidylcholine headgroups while a more rigid helix favors phosphatidylethanolamine flip. Further, the transmembrane domains of many SNARE protein subtypes share essential features with the dynamic model peptides. Indeed, corresponding peptides as well as recombinant SNAREs possess significant lipid flippase activity.