Biomolecular condensates are important for a variety of cellular functions, such as biochemical regulation, structural organization, and RNA metabolism. While the properties and physiology of these condensates depend on their structure, this important aspect has received little experimental consideration. We expect a structure-function relationship determined by protein-protein interactions. Recent simulations of disordered proteins with interactions based on the sticker-and-spacer suggest fascinating structures in the bulk and surface of condensates. We reveal the structure of biomolecular condensates using small-angle X-ray scattering. We show that condensates made from a simple model system of bovine serum albumin (BSA) and polyethylene glycol (PEG) behave like a classical liquid. We extend our approach to the structure of condensates made of disordered proteins such as fused in sarcoma (FUS), and we find that FUS inside condensates structurally behaves like a gas. Our approach is applicable to a variety of different condensates and shows that diverse condensates have diverse structures.
Lorenz et al. (Sun,) studied this question.