A coarse-grained modelling approach to protein liquid-liquid phase separation: effect of recombinant protein length on self-assembly structures.

Phase transitions play an essential role in the assembly of nature's protein-based materials into hierarchically organized structures, yet the underlying mechanisms and interactions remain elusive. A central question for designing proteins for materials is how the protein architecture affects the nature of the phase transitions and the resulting assembly. We examine the assembly of silk-like modular block proteins by a computational bead-spring model. We show that our model can underpin the transition from homogeneous solution to phase separation corresponding to assembly formation for various protein architectures, particularly protein chain length variation [1]. We find that in the assembly phase, a protein length- and concentration-dependent transition between two distinct assembly morphologies, one forming aggregates, and another coacervates, exists, both in the simulations and in our experimental characterization of the equivalent proteins with varying lengths. We deduce that properties and internal structures of the assemblies depend on the protein size. Our experimental data of silk-mimicking proteins support the model predictions. This approach can be extended to investigate other protein design variables.

[1] Lemetti et al., Biomacromolecules 23 (8), 3142–3153 (2022).