Engineering Peptide-Based Synthetic Condensates

Biological condensates (membraneless organelles) are liquid droplets consisting of proteins and nucleic acids that form within cells via liquid-liquid phase separation. These droplets are dynamic, have been shown to coalesce within cells, and can form and dissipate in response to biological and environmental signals. Many condensates have multiphase structure where different cellular components are sequestered into different layers, each with their own function. Here we discuss designing synthetic condensates to understand the role of diverse molecular interactions within proteins on biological phase separation, investigate the encapsulation of small molecules and enzymes, and establish design rules for multiphase formation. The synthetic condensates are formed via complex coacervation of oppositely charged polypeptides. Complex coacervation is a liquid-liquid phase separation that occurs via enthalpic charge interactions and entropic effects from the release of counterions and hydration water. We have created a library of different polypeptide sequences that incorporate various charge patterns, hydrophobic amino acids, and aromatic amino acids in the sequence. In addition, our sequences incorporate different chiral patterns of amino acids that bias the formation of liquid complex coacervates by preventing hydrogen bonding between the polypeptides know to form solid polyelectrolyte complexes. With this library we aim to explore the effects on the stability, encapsulation selectivity, and materials properties of the coacervate phase. Moreover, we mix coacervate phases with different interfacial tensions to create multiphase droplets.