Viscoelasticity of globular protein-based biomolecular condensates

Dynamic light scattering microrheology unveils the impact of folded
protein domains on biomolecular condensate viscoelasticity across multiple
time scales. The phase separation of biomolecules into biomolecular
condensates has emerged as a ubiquitous cellular process. Understanding
how intrinsically disordered protein sequence controls condensate
formation and material properties has provided fundamental biological
insights and led to the development of functional synthetic condensates.
While these studies provide a valuable framework to understand subcellular
organization via phase separation they have largely
ignored the presence of folded domains and their impact on condensate
properties. We set out to determine how the distribution of sticker
interactions across a globular protein contributes to rheological
properties of condensates and to what extent globular protein-containing
condensates differ from those formed from two disordered components. We
designed three variants of green fluorescent protein with different charge
patterning and used dynamic light scattering microrheology to measure the
viscoelastic spectrum of coacervates formed with poly-lysine over a
timescale of 10−6 to 10 seconds, elucidating the response of protein
condensates in this range for the first time. We further showed that the
phase behavior and rheological characteristics of the condensates varied
as a function of both protein charge distribution and polymer/protein
ratio, behavior that was distinct to condensates formed with folded
domains. Together, this work enhances our fundamental understanding of
dynamic condensed biomaterials across biologically relevant length- and
time-scales.