From Physiological Fluids to Pathological Gels: Disordered Proteins at the Nexus of Liquid Phase Separation and Neurodegenerative Disease

Disordered protein domains are emerging as key players in driving the assembly of both pathological fibrous aggregates and functional RNA/protein (RNP) bodies with liquid-like properties. However, the molecular mechanisms governing protein assembly into either liquid-like or solid-like gel states are yet to be understood. Here, we combine soft matter and biochemical approaches to examine the relationship between diverse assembly states of several disordered RNP model proteins. Building on our recent work revealing that protein droplet viscosity and dynamics could be tuned by exogenous substrates or conditions, we investigate the maturation and non-equilibrium dynamics of droplets over time. We use several complementary microrheology approaches, including a new microfluidic platform, to measure precise viscoelastic changes in protein droplet material properties. We also use fluorescence recovery after photobleaching (FRAP) and biochemical aggregation assays to probe the dynamics and solubility states of protein components. Together, this work provides mechanistic insight into the relationship between diverse protein assembly states and the way in which disordered protein and protein/nucleic acid interactions give rise to mesoscopic materials with unique properties.