We have employed a model system, inspired by SNARE proteins, to facilitate membrane fusion between Giant Unilamellar Vesicles (GUVs) and Large Unilamellar Vesicles (LUVs) under physiological conditions. In this system, two synthetic lipopeptide constructs comprising the coiled-coil heterodimer-forming peptides K4, (KIAALKE)4, or E4, (EIAALEK)4, a PEG spacer of variable length, and a cholesterol moiety to anchor the peptides into the liposome membrane replace the natural SNARE proteins. GUVs are functionalized with one of the lipopeptide constructs and the fusion process is triggered by adding LUVs bearing the complementary lipopeptide. Dual-colour time lapse fluorescence microscopy was used to visualize lipid- and content-mixing. Using conventional confocal microscopy, lipid mixing was observed on the lipid bilayer of individual GUVs. In addition to lipid-mixing, content-mixing assays showed a low efficiency due to clustering of K4-functionalized LUVs on the GUVs target membranes. We showed that, through the use of the non-ionic surfactant Tween 20, content-mixing between GUVs and LUVs could be improved, meaning this system has the potential to be employed for drug delivery in biological systems.

J Heyrovský Institute of Physical Chemistry Academy of Sciences of the Czech Republic v v i Dolejškova 2155 3 182 23 Prague 8 Czech Republic

Supramolecular and Biomaterials Chemistry Leiden Institute of Chemistry Leiden University P O Box 9502 2300 RA Leiden The Netherlands

Supramolecular and Biomaterials Chemistry Leiden Institute of Chemistry Leiden University P O Box 9502 2300 RA Leiden The Netherlands Macromolecular Biochemistry Leiden Institute of Chemistry Leiden University P O Box 9502 2300 RA Leiden The Netherlands

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