LAUSR

Non-vesicular lipid transport between bilayers at membrane contact sites plays important physiological roles. Mechanistic insight into the action of lipid-transport proteins localized at these sites requires determination of the distance between bilayers at which this transport can occur. Here we developed DNA-origami nanostructures to organize size-defined liposomes at precise distances and used them to study lipid transfer by the synaptotagmin-like mitochondrial lipid-binding protein (SMP) domain of extended synaptotagmin 1 (E-Syt1). Pairs of DNA-ring-templated donor and acceptor liposomes were docked through DNA pillars, which determined their distance. The SMP domain was anchored to donor liposomes via an unstructured linker, and lipid transfer was assessed via a Förster resonance energy transfer (FRET)-based assay. We show that lipid transfer can occur over distances that exceed the length of an SMP dimer, which is compatible with the shuttle model of lipid transport. The DNA nanostructures developed here can also be adapted to study other processes occurring where two membranes are closely apposed to each other. Use of DNA-origami nanostructures to study lipid transfer between closely apposed membrane bilayers supports a model where phospholipids are transferred by extended synaptotagmin 1 between the endoplasmic reticulum and plasma membrane through a shuttle mechanism.