Competition between self-assembly and phase separation induces re-entrant condensation of DNA liquids

Abstract

In many biomolecular solutions, multivalent interactions that promote complexation lead to phase separation at high concentrations. Here we study a model biomolecular system that exhibits the opposite behavior: Self-assembly into multisubunit complexes inhibits phase separation, even though the same intermolecular interactions underlie both processes. We use microfluidics-based experiments to show that DNA nanostars, which are known to phase separate at low temperatures, can also phase separate upon disassembly at high temperatures and high concentrations of divalent cations. We introduce a theoretical model that quantitatively reproduces this novel re-entrant phase behavior, providing a unified view of the competition between self-assembly and phase separation in biomolecular solutions.

Theory and Simulation of Multiphase Coexistence in Biomolecular Mixtures

“…Folded domains within multidomain proteins can also contribute to the multivalency required to drive LLPS, either through protein-protein interactions (PPIs) [29] or, in the case of RNA binding domains (RBDs), through interactions with RNA [30]. Finally, nucleic acid mixtures can phase separate under certain conditions due to intermolecular base-pairing [31][32][33] and nonspecific association [34]. Importantly, the strengths of the net interactions among biopolymers in liquid-like condensates are typically comparable to the thermal energy, since the protein and nucleic acid constituents of biomolecular condensates can often remain fluid on biologically relevant timescales.…”

“…A consequence is that the equilibrium compositions of coexisting phases may depend on the concentrations of all the components in the mixture, even when there are only two phases in coexistence. This feature can be used to detect the influence of multiple components on phase separation and to infer the relative strengths of homotypic and heterotypic interactions by measuring the volume fractions of coexisting phases at different overall mixture concentrations [33,38].…”

“…Developing theoretical tools for emerging experimental applications. A variety of experimental platforms for manipulating biomolecular LLPS have recently been developed using "designer" peptides [144][145][146][147], nucleic acids [32,33,148], and nonbiological polymers [149]. Chemically specific computational tools are needed to guide the rational design of multicomponent, multiphasic mixtures using these experimental platforms.…”