Invagination of\nGiant Unilamellar Vesicles upon Membrane\nMixing with Native Vesicles

We\ndemonstrate rapid\nmembrane mixing between GUVs of\npure lipid\ncompositions and membrane vesicles (MVs) isolated from the plasma\nmembrane of Vero cells, resulting in the transfer of native lipids\nand proteins to the GUVs. The steps involved in the membrane mixing\nare docking followed by membrane fusion. We show that positively charged\nlipids of the GUVs are essential for the docking, and the native membrane\ncomponents of MVs drive the fusion. The interleaflet and lateral asymmetry\nand a change in the membrane tension upon the membrane mixing trigger\nmembrane invagination. We detected outward and inward invagination\nsites at the rim of the GUVs within 10–40 min of the membrane\nmixing. The extent of the invaginations depends on the cholesterol\nand sphingomyelin (SM) contents in the GUVs. Cholesterol content above\na critical concentration disfavors membrane invaginations, and the\nSM lipid is an essential molecular factor for membrane invagination.