Sorting liposomes of distinct sizes by DNA-brick assisted centrifugation

Abstract

The "tiny bubbles of fluid" wrapped by lipid-bilayer membranes, termed vesicles, are abundant in cells and extracellular space, performing critical tasks including nutrient uptake, cargo transport, and waste confinement. Vesicles on different missions and transport routes are often distinct both in size and in chemical composition, which confers specificity to their interactions with other membranous compartments. Therefore, to accurately recapitulate the vesicles structure and behavior, it is important to use homogeneous liposomes (vesicles made of synthetic components) with precisely defined attributes as model membranes. Although existing methods can generate liposomes of selected sizes with reasonable homogeneity, the scalable production of uniformly-sized liposomes across a wide range of dimensions and compositions remains challenging. Here we report a streamlined, high-throughput sorting technique that uses cholesterol-modified "nanobricks" made of a few DNA oligonucleotides to differentiate hetero-sized liposomes by their buoyant densities. After DNA-brick coating, milligrams of liposomes of different origins (e.g., produced via extrusion or sonication, and reconstituted with membrane proteins) can be separated by centrifugation into six to eight homogeneous populations with mean diameters from 30 to 130 nm. In proof of concept experiments, we show that these uniform, leak-free liposomes are ideal substrates to study, with an unprecedented resolution, how membrane curvature influences the activity of peripheral (ATG3) and integral (SNARE) membrane proteins. We anticipate that our sorting technique will facilitate the quantitative understanding of membrane curvature in vesicular transport. Furthermore, adding a facile and standardized separation step to the conventional liposome preparation pipeline may benefit the formulation and prototyping of liposomal drug-carrying vehicles.