DNA cytoskeleton strengthens liposomes

Liposomes have many potential uses: as models for biological cells, as ­biosensor platforms, and as drug delivery systems. But these lipid membrane structures are fragile. To shore up these structures, Miho Yanagisawa of Tokyo University of Agriculture & Technology, Masahiro Takinoue of Tokyo Institute of Technology, and coworkers use DNA as a structural ­material to build a cytoskeleton for liposomes (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1702208114). The researchers make the cytoskeleton out of three DNA sequences that self-assemble into a Y-shaped ­double-stranded motif with overhanging pieces of single-stranded DNA. The overhangs allow the Y motifs to further assemble into larger spherical networks. Negatively charged DNA interacts with positively charged lipids in the liposome membranes to form a shell at the interior surface of the liposomes. Liposomes with the DNA structures are sturdier than ones without the cytoskeletons. For example, they are better able to withstand sudden concentration changes in their molecular surroundings, a phenomenon known as osmotic shock. But this extra stability occurs only when the DNA is in a gel phase rather than when it’s crystalline. The ­mechanical properties of the DNA gel can be controlled by changing the DNA sequence and the length of the overhangs, the researchers note.