Reconstruction of motile actin networks in giant liposome

To construct a simple model cellular system exhibiting the property of self-propelled motion, cell-sized giant liposomes encapsulating desired amounts of actoHMM, a mixture of actin filament (F-actin) and heavy meromyosin (HMM, an actin-related molecular motor), have been prepared. We adapted the methodology of spontaneous transfer of a water droplet through oil/water interface in the presence of phospholipid and successful obtained stable giant liposome with the inner physiological biopolymer solution. We introduced ATP to the bathing solution of liposome encapsulating actoHMM, in which bilayer membrane α-hemolysin, a bacterial membrane pore-forming toxin, is embedded. In this system, ATP is supplied into the inner volume of liposome through the protein pores in a passive manner. Accompanied by the ATP supply, actin networks or bundles that have encapsulated in the liposomes exhibited specific morphological change, being attributable to the active sliding between F-actin and HMM. Remarkable difference in the behavior of F-actins is found; i.e., inside the liposome, almost all the F-actins situate around the inner periphery of the liposome, whereas, in the bulk solution, actin bundles form an aster-like structure.