Synthetic biology: proteins set vesicles in motion

Reconstructing artificial cells with life-like properties from minimal components is an important goal of synthetic biology. The ability to move independently is a key property that is difficult to reconstruct in a test tube. A team led by physicists Erwin Frey, holder of the Chair of Statistical and Biological Physics at LMU, and Petra Schwille from the MPI of Biochemistry has now taken an important step forward, as the researchers report in the journal Nature Physics.

The scientists have succeeded in keeping vesicles enclosed by a lipid membrane - so-called liposomes - in constant motion on a supporting membrane. They are 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 known system for biological pattern formation: The system of Min proteins that controls cell division in the bacterium E. coli. Experiments in Schwille's laboratory have shown that in the artificial system, membrane-binding Min proteins arrange themselves asymmetrically around the vesicles and interact with them in such a way that they set themselves in motion. The proteins bind to both the supporting membrane and the vesicles themselves. „Directed transport of large membrane vesicles is otherwise only found in higher cells, where complex motor proteins are responsible for this. The fact that small bacterial proteins are able to do this completely surprised us," comments Schwille. „It is currently not clear exactly what the protein molecules on the membrane surface do, nor why bacteria might need such a function.“

Two possible mechanisms
Frey's team used theoretical analyses to identify two different mechanisms that could be behind the movement: „One possible mechanism is that the proteins on the supporting membrane interact with those on the vesicle surface as in a kind of friction lock and build or dissolve molecular bonds,„ explains Frey. If there are more proteins on one side than on the other, the frictional seal opens there, while it closes on the other. The vesicle then moves in the direction in which there are fewer proteins.“ The second possibility for a mechanism is that the membrane-bound proteins deform the vesicle membrane and change its curvature. This change in shape then causes the forward movement.

„Both mechanisms are possible in principle,

emphasises Frey. But what we know for sure is that the protein patterns on the support and on the vesicle are responsible for the movement. This means that we have taken a huge step towards an artificial cell.

The authors are convinced that their system can serve as a modelling platform for the development of artificial systems with life-like movements in the future.

Press release of the "idw - Informationsdienst Wissenschaft" from 16 May 2023