(59j) Engineering Polyelectrolyte and Protein Complexation and Phase Separation

Protein-polyelectrolyte coacervates have shown great potential in protein purification and protein delivery. However, many proteins do not form stable complexes or do not phase separate with oppositely charged polyelectrolytes. To address this challenge, the influence of protein charge density and anisotropy on complexation and phase separation with polyelectrolytes was tested by engineering model proteins. Phase separation of the engineered proteins with strong and weak polyelectrolytes has been investigated by light scattering and optical microscopy. Importantly, short polypeptide tags were found to promote complex coacervation. The length and sequence of these polypeptides was found to impact the critical salt concentration and protein concentration in the coacervate phase. The thermodynamics of the complexation of engineered proteins with a strong polyelectrolyte was measured using isothermal calorimetry. These findings have been used to design micellar assemblies for intracellular protein delivery.