Biophysics: Droplets in motion

The separation of oil and water is a classic example: phase separation, i.e. the separation of mixtures into their components, is ubiquitous in nature. Biomolecular droplets, which are formed by the phase separation of proteins and nucleic acids, have also been detected many times in the cell. They play an important role in cell biology, for example by creating a local environment for chemical reactions and are responsible for the localisation of proteins in the centre of the cell during cell division. A team led by LMU physicist Professor Erwin Frey has now investigated the behaviour of enzyme droplets and shown that they can move directionally in the cell. 

In a thermodynamic equilibrium system, large droplets grow at the expense of smaller droplets because a state with many droplets is not stable. In the cell, on the other hand, as has been shown on various occasions, the droplets are often brought out of equilibrium by the supply of energy. „This leads to completely new phenomena“, says Frey. Together with his team, he has investigated the mechanisms of triggers consisting of enzymes that catalyse chemical reactions between proteins. Using a minimal model, the researchers were able to show that these enzymatic droplets can move in a directed manner and specifically migrate to the centre of the container in closed containers.

„This property is similar to the mechanism by which protein droplets can find the centre of cells in prokaryotes (bacteria) and control correct cell division,

says Frey. Under other conditions, however, the droplets, depending on their size, can also divide and stabilise a state with many droplets. „This is in contrast to the dynamics that would be expected in thermal equilibrium,“ says Frey. „Our results emphasise the role of chemical reactions in trough formation, which is a broad and very active field of research.“

Press release of the "idw - Informationsdienst Wissenschaft" from 22 March 2023