In nature, biopolymers partition into dynamic compartments to facilitate and regulate their interactions. These dynamic compartments are referred to as membraneless organelles (e.g., nucleolus, P bodies, stress and germ granules) and consist of biopolymer rich interiors that rapidly assemble and disassemble to form liquid droplets, hydrogels or fibril structures. However, the physical interactions that affect the formation, dissolution, and regulation of these assemblages are poorly understood, yet vital in determining their function in normal and disease states. Therefore, there is a strong need to investigate the underlying mechanisms that drive dynamic biopolymer complexation and develop an understanding of their biochemical function. Interestingly, polyelectrolyte complexes produced in vitro using simple homopolymers are strikingly similar to the membraneless organelles found in vivo. Under defined conditions, oppositely charged polyelectrolytes can form complexes consisting of a dense polymer rich phase (liquid coacervate or glassy precipitate) in a polymer depleted aqueous phase. In this work, we investigate the forces that govern membraneless organelle formation by engineering model polypeptide analogs and systematically studying their phase transition behavior. Using synthetic polypeptides we are able to modify the chain length (20 – 400-mer) and monomer sequence, while keeping the backbone chemistry constant. In addition, we are able tune the polypeptide sequence to study the effects of charge density and hydrophobicity on complexation. From a broad perspective, our work holds the potential to develop a basic understanding of protein/polyelectrolyte complexation, impacting design of novel functional biomimetic materials.

Polyelectrolyte complex mimics of membraneless organelles

254th National Meeting (2017)

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