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Phys Rev Lett. 2018 Dec 21;121(25):258101. doi: 10.1103/PhysRevLett.121.258101.

Salt-Dependent Rheology and Surface Tension of Protein Condensates Using Optical Traps.

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Max-Planck-Institut für Zellbiologie und Genetik, Pfotenhauerstraße 108, 01307 Dresden, Germany.
Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzerstraße 38, 01187 Dresden, Germany.
Center for Systems Biology Dresden, Pfotenhauerstraße 108, 01307 Dresden, Germany.
Biotechnology Center, Technische Universität Dresden, Tatzberg 47-49, 01307 Dresden, Germany.


An increasing number of proteins with intrinsically disordered domains have been shown to phase separate in buffer to form liquidlike phases. These protein condensates serve as simple models for the investigation of the more complex membraneless organelles in cells. To understand the function of such proteins in cells, the material properties of the condensates they form are important. However, these material properties are not well understood. Here, we develop a novel method based on optical traps to study the frequency-dependent rheology and the surface tension of P-granule protein PGL-3 condensates as a function of salt concentration. We find that PGL-3 droplets are predominantly viscous but also exhibit elastic properties. As the salt concentration is reduced, their elastic modulus, viscosity, and surface tension increase. Our findings show that salt concentration has a strong influence on the rheology and dynamics of protein condensates suggesting an important role of electrostatic interactions for their material properties.

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