7 research outputs found
Salt-dependent rheology and surface tension of protein condensates using optical traps
An increasing number of proteins with intrinsically disordered domains have
been shown to phase separate in buffer to form liquid-like phases. These
protein condensates serve as simple models for the investigation of the more
complex membrane-less 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 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.Comment: 5 pages, 3 figures, 1 supplemen
Principles of Systems Biology, No. 11
This month: AI that learns patterns and facts, new protein-RNA and protein-protein relationships, engineering signaling and metabolism, and more variants of Cas9
Polar Positioning of Phase-Separated Liquid Compartments in Cells Regulated by an mRNA Competition Mechanism
P granules are non-membrane-bound RNA-protein compartments that are involved in germline development in C. elegans. They are liquids that condense at one end of the embryo by localized phase separation, driven by gradients of polarity proteins such as the mRNA-binding protein MEX-5. To probe how polarity proteins regulate phase separation, we combined biochemistry and theoretical modeling. We reconstitute P granule-like droplets in vitro using a single protein PGL-3. By combining in vitro reconstitution with measurements of intracellular concentrations, we show that competition between PGL-3 and MEX-5 for mRNA can regulate the formation of PGL-3 droplets. Using theory, we show that, in a MEX-5 gradient, this mRNA competition mechanism can drive a gradient of P granule assembly with similar spatial and temporal characteristics to P granule assembly in vivo. We conclude that gradients of polarity proteins can position RNP granules during development by using RNA competition to regulate local phase separation