(Nanowerk News) Creating artificial cells with life-like characteristics from a minimal set of components is a major goal of synthetic biology. Autonomous movement is the main ability here, and one that is difficult to reproduce in a test tube. A team led by physicists Erwin Frey, Professor of Statistical Physics and Biology at LMU, and Petra Schwille of the Max Planck Institute for Biochemistry, have now made important advances in this area, the researchers report in the journal. Natural Physics (“A mechanochemical feedback loop drives the continuous movement of liposomes”).
Scientists have succeeded in keeping vesicles covered by lipid membranes – which are called liposomes – in constant motion on a supporting membrane. This movement is driven by the interaction of the vesicle membrane with certain protein patterns, which in turn require the biochemical “fuel” ATP. These patterns are generated by a system known for biological patterning: the Min protein system, which controls cell division within E. coli bacteria.
Experiments in Schwille’s laboratory have shown that the membrane-binding protein Min in artificial systems arranges itself asymmetrically around vesicles and interacts with them in such a way as to move them. In the process, the protein binds both to the supporting membrane and to the vesicle itself.
“Directional transport of large membrane vesicles is otherwise only found in higher cells, where complex motor proteins perform this task. To find out that a small bacterial protein is capable of doing something similar was a complete surprise,” said Schville. “Right now it’s not clear not only what exactly protein molecules do on the surface of the membrane, but also for what purpose bacteria need such a function.”
Two possible mechanisms
With the help of theoretical analysis, Frey’s team identified two distinct mechanisms that might be behind the movement: “One possible mechanism is that proteins in the support membrane interact with those on the surface of the vesicles such as zippers and form or dissolve molecular compounds in this way,” Frey explained. “If there is more protein on one side than the other, the zipper opens there, while the other side closes. The vesicles thus move in the direction where there is less protein.
The second possible mechanism is that membrane-bound proteins deform the vesicle membrane and change its curvature. This change in shape then causes forward motion.
“Both mechanisms are possible in principle,” said Frey. “What we do know for sure, however, is that the patterns of proteins on the supporting membranes and on the vesicles cause movement. This is a big step forward towards artificial cells.” The authors believe that their system can serve as a future modeling platform for the development of artificial systems with life-like motion.