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Physicists investigate the dynamics of active protein droplets in cells

Physicists investigate the dynamics of active protein droplets in cells
Self-centering and oscillations. (a) Droplet center trajectories in simulations for different values of M; symbols indicate the position in the diagram shown in Fig. 2. The droplet center is initially at xd(0)=−l0 in a domain of size L=3l0. (b) Decay rate (black dots) and frequency (red dots) as functions of M, obtained by fitting the respective droplet trajectories. Red triangle indicates overdamped regime. (c) Relaxation rate λ as a function of k1 (bottom axis), for Mε0/D=10 and xd(0)=−0.3l0. Top axis relates the domain size to the length scale of the concentration profiles. The analytical predictions (blue line) in the quasi-steady-state approximation match our simulations (black dots). Credit: Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.128401

The phase separation of oil and water is a classic example of a process ubiquitous in nature, in which mixtures separate into their constituent parts. Scientists have also repeatedly identified biomolecular droplets in cells that originate from the phase-separation of proteins and nucleic acids. These droplets play various vital roles in cells where, for example, they create a local environment for chemical reactions, and are responsible for the midcell localization of proteins during cell division.

A team led by LMU physicist Professor Erwin Frey has now investigated the behavior of enzymatic and predicted that they can show directed self-propulsion in the cell. The study is published in the journal Physical Review Letters.

In a thermodynamic system that is in thermal equilibrium, large droplets grow at the expense of smaller droplets, thus rendering a state with many droplets unstable. In a cell, by contrast, several studies have demonstrated droplets are often driven out of equilibrium by influx of energy. "This leads to a wealth of novel phenomena," says Frey. With his team, he investigated the mechanisms of droplets made up of enzymes that catalyze between proteins. Using a minimal model, the researchers were able to show that these enzymatic droplets can direct self-propulsion and that, in closed domains, they move to the center in a directed manner.

"This property resembles the mechanism by which protein droplets find the cell middle in prokaryotes (bacteria) and can control correct ," says Frey. Under other conditions, however, the droplets, depending on their size, can also divide, resulting in a stable coexistence of multiple droplets. "This stands in contrast to the dynamics that one would expect in ," says Frey. "Our results underscore the role of chemical reactions in droplet formation, representing a broad and very active research domain."

More information: Leonardo Demarchi et al, Enzyme-Enriched Condensates Show Self-Propulsion, Positioning, and Coexistence, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.128401

Journal information: Physical Review Letters

Citation: Physicists investigate the dynamics of active protein droplets in cells (2023, March 22) retrieved 5 June 2023 from
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