A synthetic biomolecular condensate from plant proteins with controlled colloidal properties

A synthetic biomolecular condensate (sBC) consisting of a prolamin-rich, plant protein, zein, has been engineered. These artificial condensates were prepared from the liquid-liquid phase (LLP) separation of a protein-rich liquid phase in water. To ensure the colloidal stability of the separated condensate, the protein was chemically modified either via quaternization with glycidyl trimethyl ammonium chloride (GTMAC) or covalently connecting poly(ethylene glycol) by reductive amination, respectively. The modified protein condensates, termed QZs and PZs (for quaternized and PEG-conjugated zein, respectively) exhibited hydrodynamic diameters (D_H) ranging from 100-300 nm and surface charge or ζ-potential of +35 to -19 mV, which ensured condensate stability via inter-particle repulsion. The size, charge, stability, and morphology of the condensate particles can be optimized by mixing both types of modified proteins (QZs and PZs) at a pre-determined stoichiometry. Such stoichiometric interactions of proteins electrostatically and thermodynamically stabilized the sBCs. These sBCs can be enriched with small molecules, which can be exchanged with their bulk environment, showcasing their potential to compartmentalize chemical species. In vitro studies indicated cellular internalization and accumulation of sBCs depending on their surface properties. Inspired by the condensation of proteins occurring in cells via LLP, this work provides a robust, scalable strategy to design stable, functional condensates that can be used as a platform to understand the structure and function of natural condensates.