Controlled liposome fusion mediated by SNARE protein mimics

Abstract

The fusion of lipid membranes is essential for the delivery of chemicals across biological barriers to specific cellular locations. Intracellular membrane fusion is particularly precise and is critically mediated by SNARE proteins. To allow membrane fusion to be better understood and harnessed we have mimicked this important process with a simple bottom-up model in which synthetic fusogens replicate the essential features of SNARE proteins. In our fusogens, the coiled-coil molecular recognition motif of SNARE proteins is replaced by the coiled-coil E/K peptide complex, which is one-ninth the size. The peptides are anchored in liposome membranes via pegylated lipids. Here we discuss how the liposome fusion process is controlled by different parameters within the minimal model. The lipopeptide fusogens form specific coiled coils that dock liposomes together, resulting in the merging of membranes via the stalk intermediate. Unusually for model systems, the lipopeptides can rapidly lead to fusion of entire liposome populations and the liposomes can undergo many rounds of fusion. The rate and extent of fusion and the number of fusion rounds can be manipulated by adjusting the fusogen and liposome concentrations. For example, these parameters can be tuned such that tens of thousands of ∼100 nm liposomes fuse into a single giant liposome ∼10 μm in diameter; alternatively, conditions can be selected such that only two liposomes fuse. The improved understanding of membrane fusion shows how application-specific fusion attributes can be achieved, and paves the way for controlled nanoreactor mixing and controlled delivery of cargo to cells.