💥 Bioinspired Protein Droplets Swim Thanks to This Newly Discovered Physical Effect

2024-07-18 06:00:08

In cells, true chemical factories, reactions are organized by compartments, or organelles, some of which are devoid of membranes.

An international collaboration has revealed the existence of an unexpected phenomenon, called dialytaxis, in artificial organelles without membranes. According to this work published in Nature Communicationsthis effect could play a role in theorganisation cellular compartments and be exploited in bioengineering.

(top) Passive droplets are attracted to mixing-stabilizing solutes and repelled by droplet-stabilizing solutes. Opposing gradients can lead to no net motion.
(bottom) Droplets producing mixture-stabilizing solutes (resp. droplet stabilizers) swim towards (resp. away from) each other. Droplets producing competing solutes can chase each other.

Inside cells, there are well-defined compartments that regulate biochemical activity. Some, such as the nucleus, have a membrane, while others are delimited only by a liquid-liquid interface that is maintained despite the many surrounding chemical reactions.

If the properties of a liquid interface vary along itself, such as by locally adding a surfactant like soap, spontaneous flows appear and move the matter: this is what is called the Marangoni effect. It is found for example in tears of wine, these liquid beads that form above the wine when you shake your glass. glass. In this case, alcohol, whose quantity varies along the interface, plays the role of soap.

However, the vast majority of membrane-free compartments of cells do not synthesize soap or alcohol, and the Marangoni effect is therefore not supposed to be able to occur there. Researchers from the Hydrodynamics Laboratory (LadHyXCNRS/École Polytechnique), from the Swiss Federal Institute of Technology in Zurich (ETHZSwitzerland) and theCornell University (United States) have however discovered that the Marangoni effect could well take place there, according to a more generic principle than expected.

The team was studying chemical reactions inside an artificial system of enzyme-laden protein drops that mimic the membraneless compartments of cells. The scientists were looking at the reaction of urea breaking down into ammonia and carbon dioxide when they saw the protein drops begin to swim and attract each other. This behavior corresponds to the Marangoni effect. The molecules produced by the breakdown of urea, although very different from soap or alcohol, disrupt the stability of the liquid-liquid interface between the drop and the solution.

By testing different molecules, the researchers realized that the protein droplets then collectively move toward areas concentrated in molecules that dissolve them. This phenomenon, which the co-authors have named dialytaxis, could participate in the transport of membrane-free compartments inside cells.

This principle could eventually be used to design “robot droplets” that would sense variations in the chemical composition of their environment, move accordingly, and then transform into chemical microreactors at the desired location.

References:
Phase-separated droplets swim to their dissolution.
Etienne Jambon-Puillet, Andrea Testa, Charlotta Lorenz, Robert W. Style, Aleksander A. Rebane & Eric R. Dufresne.
Nature Communications volume 15, article number: 3919 (2024).
https://doi.org/10.1038/s41467-024-47889-y
Article available on the open archive database HAL

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