Nucleation pathways of multicomponent biomolecular condensates: a cautionary tale of the classical nucleation theory

Intracellular phase separation plays a crucial role in regulating important biological processes, such as transcription and DNA organization. In certain cases, condensates assemble via processes analogous to nucleation and growth in abiotic systems (e.g. first-order liquid-gas phase transition). However, a quantitative description of the nucleation landscape must also account for both the multicomponent nature of bimolecular condensates and the crowded intracellular environment.

Here, we address this question by combining theory, molecular simulation, and continuum-scale numerical methods. To illustrate the idea, we consider a 3-component system where the third component occupies only a minority volume fraction but can lower the free-energy barrier for nucleating one of the two majority components. We find that, at low mobilities and in the presence of significant thermal fluctuations, the preferred nucleation pathway can deviate significantly from predictions of Classical Nucleation Theory (CNT), in terms of both the concentration profiles and the free-energy barrier. We will discuss scenarios in which this discrepancy becomes important and the resulting biological implications.